Surface-specific performance of metal and metal oxide nanoparticles in latent fingerprint visualisation

Abstract

Latent fingerprint (LFP) visualisation remains a cornerstone method in forensic science, with ongoing developments aimed at enhancing clarity, sensitivity, and substrate compatibility. Due to their ability to tailor surface chemistry and optical properties, nanoparticles present a promising avenue for fingerprint development, especially on various types of surfaces. However, there has been a lack of understanding regarding the comparative behaviour of nanoparticles across different substrates. This review aims to address this gap by critically comparing the surface-specific performance of metal and metal oxide nanoparticles. In which we consider common nanoparticles for LFP development, such as Gold, Silver, silica, zinc oxide, Titanium dioxide, iron oxide, Copper oxide, and Aluminium oxide. Our review examines how various nanoparticles influence fingerprint residue on porous and non-porous surfaces and assesses their effectiveness in terms of clarity, durability using these nanoparticles. Our key finding of comparative analysis highlights that gold nanoparticles yield promising outcomes even on historically challenging porous substrates due to their affinity for sweat and amino acids. Conversely, zinc oxide and titanium dioxide exhibit superior fluorescence-based contrast on non-porous surfaces such as glass and plastics, as well as some porous surfaces. The rest of the nanoparticles were able to achieve their success on porous and non-porous surfaces with some limitations. We also outline diverse methods employed by various researchers, including dusting, brushing, spraying, and fluorescence imaging, while emphasising the role of substrate texture and the functionalization of nanoparticles. The review provides insights using comparative tables on selecting effective nanoparticle-based methods for specific forensic contexts to achieve more stable and universal fingerprint recovery in criminal investigations.

Graphical abstract

Illustration of various nanoparticles in forensic science for latent fingerprint Visualisation

Introduction

Nanoparticles with various morphologies have, in the last two decades, been synthesised through the techniques of nanotechnology, which find application in forensics. In the area of LFP detection, metal nanoparticles like silver or gold have been used to specifically target the residues present in the fingerprints. Such nanoparticles are frequently used to enhance sensitivity by aiming at metabolites and explosives by conjugating with antibodies and aptamers [1]. Their attributes, high surface area, smaller particle size, and good thermal and electrical conductivities are beneficial in assisting with the identification of crime scenes [2].

Apart from this, the use of metal-oxide nanoparticles such as titanium dioxide, zinc oxide, iron oxide, europium oxide, and silica nanoparticles against LFPs while purporting their effectiveness. These metal oxide powders are preferred due to their high contrast, good adhesion to fingerprint residues, and the low diminution of the image resolution, which is especially useful when the imagery is captured during daylight. These attributes accurately map the Integrated Automated Fingerprint Identification System (IAFIS) approach to tracing LFPs for criminal investigations [3, 4].

Quantum dots (QDs) such as cadmium sulfide (CdS QDs), cadmium selenide (CdSe QDs), and cadmium telluride (CdTe QDs) have been noted to have very good fluorescing properties, which are useful in fingerprint Visualisation on both porous and non-porous substrates [5]. Quantum dots have been known to possess high quantum yield, good emission light spectrum, large surface area, small size, and are stable after exposure to light. These properties enable them to interact with fingerprint residues and provide clearer images, better visibility, and sharper ridge patterns [6].

Moreover, other functionalized nanoparticles, which include carbon dots (CDs), polymer dots, fluorescent silica nanoparticles, fluorescent mesoporous silica nanoparticles, conjugated-polyelectrolyte dots (CPEDs), aggregation-induced emission luminogens (AIEgens), and rare earth metal-based fluorescent nanomaterials, are used for detecting LFPs. The use of these nanoparticles is due to their capability of producing quality images with a high background contrast, excellent specificity, and increased sensitivity. The adaptability and effectiveness of these nanomaterials have widened the scope of tools used by forensic specialists, enabling them to reliably pinpoint persons implicated in the crime [7, 8].

It has been established that the synthesis of nanoparticles can be broadly categorised into two approaches, namely the top-down and the bottom-up approach, as depicted in Fig. 1. The Top-Down method also includes Mechanical milling, which is a method of grinding bulk materials into nanosized particles through the fracture of particles using the milling balls, and Sputtering, which involves the bombardment of particles with high kinetic energy, which are then deposited onto a substrate material. In addition, laser ablation is another technique wherein a high-power laser is directed at bulk (target) material, and as a result, metallic nanostructures are produced. Chemical etching is also applicable in this method of operation by using electively reactive chemicals to eliminate and lower the dimensions of the target material. On the contrary, the Bottom-Up approach builds nanoparticles from the smaller building blocks. Such as sol–gel synthesis, where sol-solution is allowed to polymerise into gel form, and gels can sinter into nanoparticles, and laser pyrolysis, where laser energy initiates reactions that depend on reducing agents to form nanoparticles. Using biological methods, which is a subdivision of the Bottom-Up techniques, plants, yeast, or even bacteria are used for the eco-friendly synthesis of nanoparticles. The top-down approach has different categories, such as sputtering, chemical etching, mechanical milling, and laser ablation, shown in Fig. 1.

Fig. 1.

Different Synthesis methods are used for nanoparticle

Metal nanoparticles used for latent fingerprint development.

Gold nanoparticle

A Comparative overview of key studies employing gold nanoparticles, in Table 1, shows the different technologies opted for development (AuNPs) for LFP. Early foundational work by Sametband et al. [4] produced cleaner impressions that developed more quickly (1–2 min) than non-pretreated impressions (10–15 min) on porous surfaces. On non-porous surfaces, a two-step process produced high-quality prints, while Ag-PD alone produced poor impressions. Rinsing the paper with petroleum ether after immersion with AuNPs did not significantly decrease the background but increased print strength slightly.

Table 1.

A Comparative overview of key studies employing gold nanoparticles (AuNPs) for latent fingerprint visualisation

References	Surface type	Nanoparticle behavior	Clarity of latent fingerprints	Method used	Instrument(s) used	Results from instruments	Additional observations
Kolhatkar, et al. [14]	Non-Porous (Glass)	AuNPs (~ 15–20 nm) preferentially attached to fingermark ridges; minimal attachment in grooves	High clarity with distinct ridge patterns; ridge width 200–400 µm; enhanced luminescence and SERS signals	Single-Metal Deposition (SMD) using AuNPs, followed by SERS imaging	He–Ne laser (632.8 nm), AIST-NT OmegaScope 1000, Nanofinder 30 Raman spectrometer	Enhanced luminescence observed on ridges; SERS signals corresponding to biomolecules (proteins, lipoproteins, DNA, amino acids) detected; spatial mapping correlated with fingermark patterns	AuNPs provided dual functionality, visual enhancement and chemical profiling; the method demonstrated potential for non-destructive forensic analysis on non-porous surfaces. Electrostatic and chemical affinity between AuNPs and organic residues on ridges; hydroxylamine facilitates AuNP growth at residue sites; grooves lack binding sites
Shenawi et al. [11]	Porous (Paper)	AuNPs capped with mercaptocarboxylic acids bind to cellulose in areas not covered by fingerprint residues; subsequent silver deposition enhances contrast	High clarity with sharp contrast; negative images where ridges remain uncoloured against a darkened background	Immersion of paper in AuNP solution, followed by silver enhancement	Visual observation	High-contrast negative images of fingerprints were observed visually	Technique less dependent on sweat composition; potential for improved detection of latent fingerprints on paper
Hussain et al. [9]	Porous (A4 paper, Whatman filter paper), Non-Porous plastic petri dishes	In situ formation of AuNPs (~ 15–20 nm) directly on fingerprint ridges due to reduction by sweat components (lecithin and KI)	High clarity with distinct red to purple colouration; full development within 4 h; colour stable for at least 6 months on porous Surface, nonporous surface has less clear fingerprint development compared to porous materials	Immersion of substrates with latent fingerprints in 1 mM HAuCl₄·3H₂O solution at room temperature	FESEM, UV–Vis Spectroscopy, Visual Observation	FESEM confirmed AuNP size and deposition on ridges; UV–Vis showed characteristic plasmon resonance; visual observation revealed high-contrast fingerprints	Lecithin and KI were identified as effective reducing agents in sweat; the method is also applicable for creating visible patterns using bio-inks in pens and inkjet printers; non-porous surfaces showed less effective development; developed fingerprints exhibited long-term colour stability
Sametband et al. [4]	Porous Surface (A4 Paper)	AuNPs selectively adsorb on sebaceous ridges via hydrophobic interaction	Very clear; dark ridges are visible within minutes	AuNP pretreatment (3 min) + Ag-PD	SEM, TEM, Optical Microscopy	SEM: Ridge-specific AuNP distribution, TEM: ~ 2–3 nm particles, Optical: High ridge contrast	Background slightly reduced with petroleum ether rinse; Ag-PD alone ineffective
	Non-Porous Surface (Silicon Wafer, Glass Slide, Polyethene Film)	Lipid-rich ridges attract AuNPs; silver amplifies contrast	Good clarity; not developed with Ag-PD alone	AuNP pretreatment + Ag-PD	SEM, Optical Microscopy	SEM: Clear nanoparticle accumulation along ridges, on Glass Slide Fingerprints visible only after nanoparticle + Ag-PD treatment	Demonstrated for the first time on the silicon wafer, Ag-PD alone is ineffective. Demonstrates potential for hydrophobic plastic surfaces
Tang et al. [10]	Non-Porous (Glass Coverslip and Plastic Film)	AuNPs formed via sputtering: ~ 3 nm pseudospherical particles in sebum-rich ridges; ~ 10 nm irregular nanoislands in grooves	High-contrast images with distinct pink (ridges) and blue (grooves) colouration	Gold sputtering (130 s) followed by IMS	Optical Imaging, TEM, UV–Vis–NIR, IMS	TEM: Confirmed sizes (~ 3 nm on ridges, ~ 10 nm in grooves); UV–Vis: SPR peaks at 592 nm and 660 nm; IMS: Chemical mapping of fatty acids. Plastic Film consistent SPR bands similar to glass; IMS successfully detected both endogenous and exogenous compounds	Effective without additional treatment, robust Visualisation, and chemical profiling. Plastic Film requires Pre-treatment with methanol, improved substrate cleaning, and results
	Porous Surface (White Paper)	AuNP formation is influenced by the paper’s porous, insulating nature; requires additional sputtering to boost conductivity; AuNPs deposit unevenly compared to non-porous surfaces	Clear fingerprints after an extra short sputtering step (e.g., additional 10 s) needed for optimal IMS	Gold sputtering (130 s + additional 10 s) followed by IMS	Optical Imaging, TEM, UV–Vis–NIR, IMS	Effective SPR signals were detected after enhanced sputtering; IMS mapping improved with additional gold deposition	Additional sputtering compensates for the low conductivity; slight reduction in overall clarity compared to non-porous substrates
Wei and Cui [15]	Non-porous (Blue Plastic, Foundation Box, Glass, Plastic Blue- Ray CD Discs (Smooth Side))	Au@KCC-1 nanocomposites powders adhere selectively: Au NPs (≈3 nm) are uniformly dispersed on the fibrous silica, binding preferentially to fingerprint ridges via electrostatic interactions	Blue plastic has High-contrast images with sharp, legible ridge details; minimal background staining. Foundation Box has Clear fingerprint patterns; slightly lower contrast than blue plastic. Glass has very high clarity; detailed features, including third-level (sweat pores) visible. Fingerprint images are clean with clear ridges and minimal background interference on CD Discs	Fingerprint dusting with Au@KCC-1 powders	Optical Imaging (VSC6000); FESEM/TEM; UV–Vis; DLS/Zeta Potential	Imaging shows clear ridge/furrow distinction; FESEM/TEM confirms nanoparticle size and uniform distribution; UV–Vis shows an absorption peak at 530 nm. TEM: Au NP average size 3.02 ± 0.75 nm; XPS: Confirms metallic Au; UV–Vis: SPR peak at 530 nm; optical images show high contrast and resolution. FESEM images indicate proper nanoparticle adhesion; optical imaging confirms legible fingerprint patterns	Non-porous, smooth surface; excellent adhesion without extra treatment. Substrate material enhances contrast; moderate D-values (grayscale analysis confirms higher contrast on glass than foundation box as reported). Glass offers superior imaging; highest D-values (contrast) among tested non-porous surfaces. Demonstrates applicability on electronic media surfaces, reliable adhesion, and imaging
	Porous Surface (Black Paper, Red Cardboard)	Au@KCC-1 powders exhibit selective attachment on fingerprint ridges via electrostatic interactions; slightly reduced uniformity due to the paper’s porosity	High clarity; developed prints show distinct ridges with minimal background staining. On Red Card Board, Good fingerprint clarity; sufficient contrast to reveal fingerprint details	Fingerprint dusting with Au@KCC-1 powders	Optical Imaging; FESEM; FTIR; UV–Vis	Optical images display clear, well-defined fingerprints; FESEM and FTIR confirm nanoparticle deposition and chemical compatibility. UV–Vis shows characteristic SPR signal; optical imaging reveals legible prints with clear ridge patterns; FESEM indicates good nanoparticle coverage on ridges	Despite substrate porosity, powders provide high sensitivity; contrast quantification (grayscale analysis) shows good performance. Cardboard's texture does not impede the adhesion; Au@KCC-1 powders outperform commercial powders by avoiding background staining
Cheng et al. [12]	Non-Porous (Glass)	AuNPs form ~ 3–5 nm pseudospherical particles on ridges; larger aggregates on grooves	Very high; third-level features (sweat pores) visible; clear contrast	Argon ion sputtering (60–100 s)	TEM, UV–Vis, SALDI-MS	TEM confirms ridge vs. groove NP size; UV–Vis SPR peak at ~ 530 nm; SALDI-MS detects fatty acids	AuNPs stable > 1 month; optimal sputtering improves image and chemical resolution
	Porous (Paper)	Similar behaviour, but more aggregation due to porosity; slightly less uniform NP deposition	Moderate to good; visible ridge pattern but lower contrast	Argon ion sputtering (same as above)	TEM, UV–Vis, SALDI-MS	SPR peaks are weaker; SALDI-MS still detects key fatty acids; images fade after ~ 12 days	Requires careful optimisation for porous substrates; good visual and analytical potential
Yu et al. [13]	Glass, Stainless Steel (Tweezers)	Selective binding to ridges; good dispersion; ~ 4 nm AuNCs embedded in clay matrix	Very high; strong ridge clarity; 2nd and 3rd level details visible	Powdering with AuNCs@MMT	UV–Vis, Fluorescence, SEM, TEM, XRD, IR, XPS	λ_em = 655 nm; size = 4.08 nm; no structure change in clay; high red emission	Excellent for polished surfaces; minimal background; stable for > 7 months
	Plastic, Painted Metal, Adhesive Tape	Well-distributed powders adhered despite curved and sticky surfaces	High, clear ridge details even on tricky surfaces	Optical Microscopy, SEM		Consistent adhesion; slight interference from sticky fibres on tape	Good flexibility; some photography challenges on curved surfaces
	Weighing Paper (Porous)	Binding via electrostatic interactions; slight background fluorescence interference	Moderate; visible but with reduced contrast		Fluorescence Spectroscopy, Imaging	Good, but reduced contrast due to substrate fluorescence	Usable prints; slightly lower performance than on non-porous
	Ceramic Mug (Multicoloured Surface)	Strong emission from AuNCs; excellent contrast under UV light	Very high under UV; indistinguishable under visible light		VSC5000, UV Camera, Digital Microscopy	Clear ridges and minutiae are visible under UV; invisible in ambient light	Superior for complex backgrounds; UV and green light compatible
	Plastic Blu-ray Disc	Strong adhesion; third-level ridge features (sweat pores) visualised	Excellent, well-defined contrast and fine details		Imaging Workstation, Photoshop (for enhancement)	Clear distinction between ridge and valley; fine texture captured	Demonstrated long-term stability under storage and heat

A simplified approach was adopted by Hussain et al. [9], who proposed in situ formation of AuNPs directly on fingerprint ridges using endogenous fingerprint constituents like lecithin and potassium iodide (KI). This work diverged from previous methods by eliminating the use of pre-synthesised AuNPs and enabling Visualisation through naturally occurring redox reactions. Direct AuNP formation on fingerprint residues increases contrast and stability of developed prints. Sebaceous fingerprints were collected from volunteers on A4 paper or Whatman cellulose filter paper. Substrata with LFP were submerged in an aqueous solution of gold chloride (HAuCl₄·3H₂O, 1 mM) at room temperature. Fingerprints became visible after about 1 h, with the maximum development in 4 h. Developed prints showed red to purple colouration due to the surface plasmon resonance of formed AuNPs. Lecithin and KI, natural constituents of human sweat, were found to reduce Au³⁺ to Au⁰, enabling the in situ formation of AuNPs (15–20 nm) on fingerprint residues. Plastic surfaces, e.g., petri dishes; however, the intensity of developed fingerprints over these surfaces was less vivid than over porous substrata. Shown are characteristic surface plasmon resonance absorption bands typical of AuNP formation. In the absence of sufficient reducing agents, grooves prevented AuNP formation, increasing contrast with ridges. Formed fingerprints did not fade colour for at least 6 months, indicating stability. This Method showed better results on a porous surface than on a non-porous surface.

Shifting from purely visual to combined optical and chemical detection, Tang et al. [10] employed AuNP sputtering and imaging mass spectrometry (IMS) for dual-mode fingerprint analysis. Their approach shared similarities with Wei’s dual-imaging but went further by extracting molecular signatures, including drugs and endogenous lipids. The formation of differently sized AuNPs on ridge versus groove areas reflected earlier work on morphology-based contrast and built upon it with advanced instrumentation for spatially resolved chemical mapping. In contrast to traditional techniques, the technique obtains high-contrast images and chemically resolved spatial data from endogenous (e.g., fatty acids) to exogenous compounds (e.g., drugs). Sebum fingerprints were produced by a donor on various surfaces (e.g., glass, plastic, paper). Verapamil hydrochloride was occasionally applied to mimic contamination. Fingerprints were gold sputtered using a coater with high-purity gold at 12 mA, ~ 0.04–0.05 mbar pressure in argon, for 130 s, forming nanoparticles on residues. IMS utilised matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) for chemical imaging. IMS analysis used laser intensities of 2600–3000 arbitrary units and spatial resolutions of 60–90 μm, imaging fatty acids (e.g., palmitic, stearic, oleic acid) and other fingerprint components. Fingerprint ridges that are lipid-rich produced ~ 3 nm pseudospherical AuNPs, whereas cleaner grooves favoured larger, irregular nanoislands (~ 10 nm). Non-porous substrates such as glass coverslips and plastic films gave excellent optical and chemical imaging without additional treatments. For porous surfaces, white paper was also employed; because of insulation, additional sputtering (10 s at higher current) was required for better conductivity in IMS. Without additional sputtering on porous paper, IMS mapping was less effective. High-resolution optical images exhibited clear colour contrast: ridges pink (592 nm SPR peak) and grooves blue (660 nm SPR band). TEM verified the nanoparticle size: ~ 3 nm on ridges and ~ 10 nm on grooves. Mainly consisting of sebum, these areas accommodate smaller AuNPs as the organic matrix facilitates nucleation. The AuNPs are pinkish with luminescent emission and enhance MALDI signals. Grooves containing less organic matter produce larger, irregular AuNP clusters. Varied nanoparticle morphology causes a blue shift in plasmon resonance and enhances contrast between ridges and grooves. SPR peaks at 592 nm (ridges) and 660 nm (grooves) confirm nanoparticle size and distribution.

Where Tang’s method centred on chemical analysis, Shenawi et al. [11] focused on contrast inversion via hydrogen bonding between AuNP-capping ligands (with mercaptocarboxylic acids) and cellulose substrates. Conventional methods for the development of fingerprints on porous media, such as paper, are likely to be based on the chemical components in sweat, such as amino acids, in trace amounts, and produce weak or invisible prints. Their strategy allowed for “negative” fingerprint imaging on porous surfaces by targeting the paper substrate itself rather than fingerprint residues. This represented a paradigm shift: instead of visualising what is present (residues), it visualised what isn’t, effectively expanding AuNP utility in previously difficult contexts such as paper. Here, the background is coloured, but the fingerprint ridges are not, by exploiting the inverted visualisation through hydrogen bonding between the carboxylic groups of the capping ligands and the cellulose of the paper, allowing selective silver deposition in the regions not covered with fingerprint residue. By targeting the paper substrate itself, the method circumvents reliance on the chemical composition of sweat. Several mercaptocarboxylic acids were screened, including 11-mercaptoundecanoic acid and 6-mercaptohexanoic acid. The thiol group is anchored to the gold surface, and the carboxylic acid group is left free for hydrogen bonding to cellulose. The paper was immersed in the solution of AuNPs, and the nanoparticles bound to the cellulose of the paper in the regions not covered with fingerprint residue. After rinsing, the paper was treated with a silver enhancement solution, leading to silver deposition over the AuNP-bonded areas, and thereby forming a negative image of the fingerprint. Developed fingerprints were visually examined and exhibited excellent high-contrast negative images. The study did not use advanced imaging or spectroscopic methods; the problem was the visual quality of printed fingerprints. The fingerprint residues serve as a mask, preventing the AuNPs from binding to the cellulose underneath. Where there are no fingerprint residues, the AuNPs bind to the cellulose through hydrogen bonding. The subsequent deposition of silver produces a dark background and clear, uncoloured ridges. Best results were achieved using AuNPs capped with 3-mercaptopropionic acid. It developed fresh and 14-month-old fingermarks as negative impressions with high contrast and resolution. A similar dual-purpose approach was adopted by Cheng et al. [12] using sputtered AuNPs for both imaging and mass spectrometric analysis via surface-assisted laser desorption/ionisation mass spectrometry (SALDI-MS).

Like Tang, they demonstrated high-resolution optical contrast and molecular fingerprinting, but they also emphasised particle size distribution and the biocompatibility of gold. Cheng’s work validated AuNP versatility across substrates like paper and glass, reinforcing earlier conclusions about substrate-dependent performance. The premise of the method was to develop a clean, stable, and dual-use technique that not only could increase the optical contrast of fingerprint ridges but also enable detailed molecular analysis by SALDI-MS. Gold, because of its chemical stability and intense surface plasmon resonance (SPR) effect, was investigated independently of its alloys with silver to evaluate its potential as a single-component fingerprint development reagent. The process deposited AuNPs onto fingerprints on paper and glass substrates. Sputtering employed a gold target with argon for 60–100 s. This yielded small particle sizes (3–5 nm) on oily sebum-rich ridges and agglomerates with larger particle sizes in cleaner grooves. The nanoparticle morphologies created a contrast: ridges were pink-coloured because of an SPR peak at 530 nm, whereas the grooves emitted a purple-blue colour because of the red-shifted SPR response from larger-sized particles. Optical Visualisation of clear fingerprints without chemical dyes was enabled through this colour change. AuNPs mostly stuck to organic and lipophilic units in fingerprint ridges, i.e., fatty acid residues and amino acid residues. These units were involved in stabilising and aiding the nucleation of AuNPs, while grooves lacked such material content and hence experienced uncontrolled nucleation. Thus, there was a significant visual and morphological contrast in the ridge and groove regions. This was also supported by TEM, which reiterated the size difference between nanoparticles in both regions. The same was established by UV–Vis spectroscopy, with clear SPR peaks for ridge-deposited AuNPs around a fixed 530 nm. Palmitic, oleic, and stearic fatty acids were detected, demonstrating AuNPs' dual role as mass spectrometry matrices and imaging agents. Glass showed the best imaging performance, where fingerprints had high contrast and resolution for more than a month. On paper, fingerprint clarity was maintained, but contrast was reduced after about 12 days because of substrate absorbency. AuNPs still enabled successful visual and chemical analysis on paper, nonetheless. The research experimented with different compositions of alloys, but gold sputtered pure gold samples demonstrated that AuNPs can create stable, high-contrast LFP on a variety of surfaces. The ease of the sputtering process, combined with the biocompatibility and longevity of gold, makes AuNPs a candidate for application in forensic applications where visual identification and molecular analysis of fingerprint residue are needed. The authors did not mention the quantity of fingerprints that were tested, but results were replicable on every sample of the different surface materials, with little failure on glass or paper.

This research demonstrates the effective application of AuNPs to contemporary forensic fingerprint identification. In a shift toward fluorescent imaging, Yu et al. [13] introduced gold nanoclusters immobilised on montmorillonite (AuNCs@MMT) as a safer and more stable alternative to traditional powders. Their use of red fluorescent emission under UV light offered high visibility on both porous and non-porous surfaces. This powder overcomes the drawbacks of traditional methods, including the toxicity of cadmium-based quantum dots and operational complexity. To enhance dispersion and usability for powder-based fingerprint detection, the AuNCs were immobilised on Na⁺-MMT clay through electrostatic interaction (verified by a zeta potential of − 28.4 mV), creating the final AuNCs@MMT nanocomposite. The AuNCs synthesised were around 4.08 nm in diameter, verified by TEM and HRTEM imaging. They showed intense red fluorescence with an emission peak at 655 nm and an excitation maximum at 525 nm. The photoluminescence was stable under both UV (365 nm) and green light, which is important in avoiding background fluorescence and reducing UV exposure risks. The AuNCs were well dispersed in the MMT clay, which enhanced their fluorescence emission and avoided agglomeration. The nanocomposites maintained the structural integrity of the clay, as verified by XRD and IR spectroscopy, and did not show any signal of elemental gold in EDX due to low relative content. LFPs were collected by a single donor on a range of porous and non-porous substrates: glass slides, plastic, stainless steel (tweezers), painted metal (binder clips), porcelain enamel, adhesive tape, weighing paper, and a multicoloured ceramic mug. High-quality fingerprints were developed within one hour using conventional powdering techniques. The developed prints exhibited bright red fluorescence under UV light with minimal background staining, especially on polished surfaces like glass and stainless steel. Even third-level details such as sweat pores and second-level minutiae were visible under magnification. On porous substrates like weighing paper, the AuNCs@MMT nanocomposites produced visible fingerprint patterns, although background fluorescence from the substrate slightly reduced contrast. Despite this, the developed prints remained usable. SEM images revealed strong, selective adherence of the powders to fingerprint ridges via electrostatic interactions with oily and moist residues, while deposition in grooves was minimal. This ridge-specific binding, along with the clear red fluorescence under UV light, enabled distinct ridge-valley contrast. On non-porous surfaces such as glass, stainless steel, and plastic, the prints exhibited sharp, high-contrast ridge details with very low background staining. Similarly, on complex multicoloured surfaces like ceramic mugs, the red fluorescence provided excellent contrast even when ridge details were barely visible under normal lighting. The powder retained both its fluorescence and fingerprint-developing capability after 7 months of ambient storage, including exposure to high summer temperatures (> 30 °C), confirming the stability and practicality of AuNCs@MMT nanocomposites for in-situ forensic applications. Adding a spectroscopic edge,

Kolhatkar et al. [14] combined Single-Metal Deposition (SMD) with Surface-Enhanced Raman Spectroscopy (SERS) to achieve high-contrast Visualisation and chemical identification. This study echoed earlier dual-imaging methodologies by Tang and Cheng but introduced a powerful vibrational spectroscopy layer for biomolecular identification, highlighting the evolving sophistication in AuNP-enabled fingerprint analysis. Leverage the plasmonic properties of AuNPs, this procedure is aimed at enhancing both the luminescence and Raman signals of fingermark residues to enhance Visualisation and chemical profiling. The fingerprints were deposited on a glass slide non non-porous nature, then Immersion in a colloidal gold solution (AuNPs synthesised from HAuCl₄ and trisodium citrate dihydrate). Immersion in a solution of HAuCl₄ and hydroxylamine hydrochloride to enhance gold deposition. A He–Ne laser (632.8 nm) was used for excitation, and AIST-NT OmegaScope 1000 with a Nanofinder 30 Raman spectrometer captured the luminescence and Raman signals, then spatial mapping was performed to correlate the luminescence intensity to the fingermark ridge pattern for SERS measurements. AuNPs (15–20 nm) bound preferentially to fingermark ridges because of the presence of organic residues. The grooves showed minimal nanoparticle attachment and thus lower luminescence and Raman signals. Performance on porous surfaces was not evaluated. Enhanced luminescence allowed Visualisation of fingermark ridges with widths of 200–400 μm. AuNPs bind to organic residues (e.g., amino acids, lipids) along ridges of latent fingermark. The binding is facilitated by Electrostatic affinity between AuNPs and fingerprint residues. Catalytic growth on biomolecules in the secondary gold reduction step. Grooves, being residue-poor, are mostly nanoparticle-free, resulting in high contrast in optical and spectroscopic imaging. Biomolecular markers (C–H, C–C, amide, phosphate) on the fingerprint ridges. Most recently, Wei and Cui [15] synthesised Au@KCC-1 nanocomposites—gold-decorated, amine-functionalized silica nanospheres—that provided strong electrostatic interactions with negatively charged fingerprint residues.

Their work integrated the chemical selectivity of Shenawi’s approaches with the surface versatility and stability observed in Yu’s fluorescent powders. Their powder formulation demonstrated lasting activity and strong ridge selectivity on both porous and non-porous substrates. Wei and Cui prepared a sensitive, selective, and stable powder by in-situ growing Au NPs on a fibrous nano-silica support (KCC-1), which is first aminopropyl-functionalized (KCC-1-NH₂). Small Au NPs and accessibility of active sites of KCC 1 enhance adhesion to negatively charged fingerprint residues and show clear third-level features and ridge details on various surfaces. This research bridges the gap between conventional powders and advanced fluorescent nanocomposites. Hydrothermal synthesis was obtained by dissolving tetraethyl orthosilicate (TEOS) in a solution of cyclohexane and 1-pentanol, addition of cetyl pyridinium bromide (CPB) and water-soluble urea under stirring for 30 min, and then heating at 90 °C for 10 h. The product was washed and calcined at 550 °C for 6 h. Refluxing was carried out for 12 h of KCC 1 (0.2 g) with 3 aminopropyltriethoxysilane (3 APTES, 0.36 g) in toluene under a nitrogen atmosphere. KCC 1 NH₂ was separated from the mixture by washing with ethanol. KCC 1 NH₂ (0.2 g) was dispersed into 100 mL of water and stirred with 3 mL hydrogen tetrachloroaurate(III) trihydrate (HAuCl₄·3H₂O, 0.0099 g) for 3 h. Excess sodium borohydride (NaBH₄) was used to reduce Au³⁺ ions. The reaction was for 3 h, immobilising Au NPs onto KCC 1 NH₂ fibres. Final Au@KCC 1 nanocomposites were filtered and dried. Analysis by ICP indicated an Au loading of 1.66 wt%. Au@KCC 1 powders were used as fingerprint powders on various surfaces: Non-Porous: Blue plastic, foundation box, glass, and smooth plastic Blu-ray discs. Porous: Red cardboard and black paper. Treated fingerprints were visualised by a VSC6000 workstation under visible light. FSSEM and TEM established the fibrous nature of KCC 1 and its spherical microsphere size (~ 313 nm) with fibres ~ 33.66 nm apart. Au NPs, of average size 3.02 ± 0.75 nm, were immobilised evenly on the fibres without agglomeration. UV Vis Spectroscopy exhibited maximum absorption at 530 nm, as expected of Au NP size. Fourier Transform Infrared Spectroscopy (FTIR) established bands for Si–OH, condensed silica, and C–H stretching of grafted 3 APTES. XRD established amorphous silica without prominent Au peaks (due to low loading), whereas XPS established the chemical state of Au. DLS established particle size distribution of KCC 1 (~ 314 nm) and a zeta potential of + 25.54 mv for Au@KCC 1, as would be expected from electrostatic interactions with negatively charged fingerprint residues. Amino-functionalized KCC 1 guarantees strong Au NP binding, which attracts them to negatively charged fingerprint components (amino acids, proteins). Accordingly, powders selectively attach to papillary ridges, with minimal furrow deposition. Latent prints developed with powders of Au@KCC 1 exhibited high sensitivity, selectivity, clear ridge detail, and detectable sweat pores. Grayscale analysis exhibited maximum contrast between the ridges and furrows, with glass exhibiting a D value greater than the base box. All supports produced legible fingerprints, including porous ones like black paper and red cardboard, upon which Au@KCC 1 was superior to market powders. The powders remained active for 6 months of dry storage.

Silver nanoparticle

Silver nanoparticles (AgNPs) have emerged as a versatile alternative to conventional reagents in the development of LFPS, particularly due to their tunable size, surface charge, and high affinity for fingerprint residue components. Table 2 shows the detailed comparative analysis of the approach used for various porous and non-porous surfaces. Prasad et al. [16] demonstrated a cost-effective approach for enhancing fingerprint visibility on porous surfaces, such as white paper, using chemically synthesised AgNPs. AgNPs engage better with fingerprint residues, offer better stability, and produce clearer ridge patterns at lower silver nitrate concentrations.

Table 2.

A Comparative overview of key studies employing Silver nanoparticles (AgNPs) for LFP Visualisation

Study	Surface type	Nanoparticle behavior	Clarity of LFPs	Method used	Instrument(S) used	Results from instruments	Additional observations
[16]	Porous (Paper)	Good adhesion due to electrostatic interaction	Clear ridges, bifurcation, core, delta, etc	Spray after acid wash	HR-TEM, UV–Vis, Camera	HR-TEM: 10.66–14.44 nm; UV–Vis: SPR at 400–402 nm	Best clarity at 0.01 M; stable > 30 days; 17 fingerprints per concentration tested
	Non-porous	Poor interaction; no absorption or nucleation	No successful development	Spray method	Not effective—no further testing done	N/A	AgNPs are unsuitable; lack of absorption, poor adherence
Barros et al. [18]	MALDI Target Plate (metal, non-porous)	High silver ion yield; strong analyte interaction via SALDI	Strong ion peaks; detection of squalene and exogenous chemicals	Drop-coating with AgNPs	UV–Vis, DLS, Zeta potential, MALDI-TOF MS	SPR peak at 420 nm; 25.94 nm size; − 33.4 mV Zeta; ion intensities > 20 × stronger than AgNO₃	3 donors tested; 3 regions per print analyzed; reproducible results; no matrix interference
Alves et al. [19]	Stainless Steel	Dendritic AgNPs, less dense	Good (Grade 3–4) up to 1 month; moderate after	Electrodeposition	CV, SEM, Nikon D5500, Griaule® Software	SEM: contrast 4.0; dendrites on both ridges and valleys after 30 days	Reduced contrast after 30 days due to surface passivation
	Copper	Dense, uniform nanoparticle carpet	Excellent (Grade 4 for 90.48% samples)	Electrodeposition	SEM, CV, MATLAB image analysis	SEM: contrast 3.5; uniform AgNP layer in grooves	Maintains clarity up to 1 year
	Brass	Highly selective deposition; compact structure	Outstanding (Grade 4 for 97.62% samples)	Electrodeposition	SEM, CV, Griaule®, MATLAB	SEM: contrast 15.5; excellent ridge vs groove contrast	Best overall performance and stability
	White paper (porous)	Spherical, stable AgNPs; lower ACG gives a smaller size and better dispersion	0.5 mg/mL ACG-AgNP revealed 20 minutiae (1 h), 11 (24 h); higher concentrations yielded fewer points	5-s immersion	UV–Vis, TEM, AFM, NTA, Zeta potential, Nikon D3200, AFIS	SPR at 400 nm; size ~ 83.5 nm (0.5 mg/mL), − 31 to − 34 mV zeta; high stability and selectivity	Best results from 0.5 mg/mL due to smaller size and lower aggregation; effective even after 24 h

Negatively charged nanoparticles are generated through a reduction process that draws positively charged fatty acids in fingerprint residues under acidic conditions. AgNPs were synthesised by a wet chemical process using varying concentrations of silver nitrate (0.1, 0.01, and 0.001 M), and their characterisation was done by UV–visible spectroscopy and high-resolution transmission electron microscopy (HR-TEM). At 0.001 M, AgNPs were irregular (~ 10.66 ± 1.22 nm); at 0.01 M, spherical (~ 12.50 ± 2.64 nm); at 0.1 M, agglomerated (~ 14.44 ± 2.68 nm). UV–Vis spectroscopy revealed surface plasmon resonance (SPR) peaks at 400–402 nm. HR-TEM confirmed nanoparticle formation and size difference.

Fingerprints were developed on porous white paper from volunteers by a spray method after acetic acid treatment to neutralise alkaline fillers that can interfere with nanoparticle interaction. Developed prints showed excellent clarity in ridge details (bifurcations, deltas, core, short ridges, ridge endings). Fingerprints remained clear for over 30 days, far exceeding AgNO₃, which faded in about 20 days. The attraction between negatively charged AgNPs and positively charged sebaceous residues ensured strong adherence mainly to ridges, not grooves. While this approach yielded promising results on paper, further refinement in synthesis and surface interaction was explored in subsequent studies.

Building upon this chemical synthesis foundation, Brandão et al. [17] introduced a greener method for AgNP production using acetylated cashew gum (ACG) as both a stabiliser and a reducing agent. This innovative approach addresses the limitations of traditional fingerprint developers like ninhydrin and silver nitrate, which are expensive, time-consuming, and unfriendly. The authors used a biodegradable, low-toxicity polymer of Anacardium occidentale (cashew tree) to design a low-cost, rapid, and easy nanoparticle synthesis method for in-field forensic use. The nanoparticles were reduced from 1 mM silver nitrate using sodium borohydride in the presence of ACG at varying concentrations. The synthesis was confirmed by UV–Vis spectra and NTA data. The lowest concentration (0.5 mg/mL) produced the smallest and most monodisperse AgNPs (mean diameter: 83.5 ± 2.3 nm, mode: 46.4 nm), while increasing concentrations yielded larger and aggregated particles. TEM and AFM analysis showed that all ACG-AgNPs were mostly spherical but displayed different levels of aggregation, particularly at high concentrations of ACG.

The zeta potential values were very negative in all samples ( − 31.2 to − 34.1 mV), showing very good colloidal stability and high electrostatic interaction potential with the positively charged fingerprint secretions residues. The 0.5 mg/mL ACG-AgNPs performed better, detecting 20 min in 1-h-old and 11 minutiae in 24-h-old fingerprints. By comparison, the 5.0 mg/mL sample only detected 6 minutiae in the 1-h-old print, and the 1.0 mg/mL sample exhibited poor contrast due to over-aggregation. The improved performance of lower ACG concentrations was attributed to reduced nanoparticle size, higher dispersion, and better surface interaction, enabling better resolution of fingerprint ridge details. Theoretical modelling and DFT simulations validated these results, showing that ACG-AgNPs exhibit local chemical reactivity and electrostatic behaviour similar to traditional reagents.

While Prasad and Brandão established the usefulness of AgNPs on absorbent surfaces, Barros et al. [18] transitioned this research to non-porous metallic substrates by utilising green-synthesised AgNPs in combination with Surface-Assisted Laser Desorption/Ionisation Time-of-Flight Mass Spectrometry (SALDI-TOF MS). The study found that AgNPs exhibit unique optical and electrochemical features, reducing environmental and health risks and improving fingerprint detection. Latent fingerprints were deposited on MALDI plates and treated with either α-CHCA or green-synthesised AgNP suspension. Mass spectra were obtained in reflector-positive ion mode, with fingerprints examined at three spots for reproducibility. The study employed a harmless and scalable strategy to biologically synthesise AgNPs, using no toxic stabilisers or reducers. The results showed that AgNP-treated fingermarks generated significantly stronger mass spectral signals than untreated samples and samples treated with α-CHCA or AgNO₃ solution. Principal silver ion peaks were at least 20 times stronger in AgNP-treated samples than in AgNO₃. The study also indicated that silver's attraction to squalene, mainly in sebaceous secretions along ridges, mirrors selective interaction with fingerprint ridges. In this study, non-porous metal substrates, such as MALDI plates and aluminium foil, were used. Fingerprint detail could be visualised on aluminium foil using the AgNP suspension without preconditioning or UV treatment, but no spectrometric data were provided. No porous surfaces were examined, and an opening for further research is mentioned.

Despite its success, both studies were limited to porous substrates, prompting the need to explore techniques suitable for metallic and non-porous surfaces. Further refining AgNP use on metallic surfaces, Alves et al. [19] introduced an electrochemical technique for fingerprint development on stainless steel, copper, and brass. This method relied on potentiostatic deposition, where AgNPs formed only in the fingerprint furrows (grooves), generating high-contrast negative images. The controlled, non-toxic procedure offers enhanced clarity and durability even on aged samples and real-world items like keys and coins.

The study collected sebaceous fingerprints from a female donor and deposited them on pre-cleaned stainless steel, copper, and brass substrates. The AgNPs were electrochemically deposited from an aqueous electrolyte containing 5 mM AgNO₃ and 5 mM KNO₃ under potentiostatic control at − 0.35 V vs. Ag/AgCl, with deposition times ranging from 80 to 200 s depending on the substrate. The developed fingerprints were analysed using scanning electron microscopy (SEM), Nikon D5500 camera imaging, the Griaule® Forensic Fingerprint software, and the UK Home Office grading system.

Substrate-dependent variation in nanoparticle morphology was observed, with stainless steel exhibiting dendritic and loosely dispersed structures, while copper and brass surfaces exhibited more compact and uniformly agglomerated nanoparticle carpets. Brass exhibited the best performance, with 97.62% of fingermarks graded as level 4 using the UK Home Office scale. Copper followed with 90.48% at level 4, while stainless steel yielded 33.33% at level 4 and 26.19% at level 2 (potentially identifiable). The method demonstrated excellent stability in long-term ageing assessments, with high-quality images obtained even from fingermarks aged up to one year under ambient conditions. Quantitative contrast analysis of the SEM images confirmed the presence of critical minutiae, including ridge endings, bifurcations, deltas, and cores.

Silica nanoparticle

The synthesis of silica nanomaterials for latent fingerprint Visualisation has progressed in fluorescence efficiency, surface adhesion, environmental friendliness, and simplicity. Table 3 shows a Comparative overview of studies employing Silica nanoparticles for LFP Visualisation. Divya et al. [20] demonstrated that amphiphilic Pt(II) complex-functionalized silica nanoparticles successfully visualised fresh and aged fingerprints under visible and UV light (365 nm), with high-resolution ridge details on porous and non-porous surfaces. These nanoparticles were synthesised through the Stöber process employing TEOS in ethanol and ammonium hydroxide to obtain monodispersed SiO₂ particles (~ 135 ± 10 nm). Fingerprints were taken on different surfaces—glass, white notebook paper, black notebook paper, steel, and wood—and developed with forensic brushes. The non-fluorescent powders SiO₂–4 (C11H23) and SiO₂–5 (C17H35) exhibited maximum visibility in daylight to display Level 1 to Level 3 ridge detail. SiO₂–6, a fluorescent powder, performed best overall under UV light, with high luminescence and compatibility with semi-porous and non-porous surfaces. The white paper had poor contrast with non-luminescent powders but was compatible with SiO₂–6. Both SiO₂–4 and SiO₂–6 were able to develop prints up to 45 days old, proving their stability. Solving environmental issues, Rajan et al. [21] prepared fluorescent silica nanoparticles (SNPs) from rice husk waste by employing natural dyes such as curcumin to increase photoluminescence without compromising on non-toxicity.

Table 3.

A Comparative overview of key studies employing Silica nanoparticles for latent fingerprint Visualisation

Study	Surface type	Nanoparticle behaviour	Clarity of latent fingerprints	Method used	Instrument(s) used	Results from instruments	Additional observations
Oliveira et al., [25]	Stainless Steel and Glass	Steel has Ridge-selective adhesion, Glass has uniform coverage	Steel: Grade 4; 38 minutiae, Glass: Grade 3–4; 24 minutiae	Powder Dusting + UV	SEM, TEM, PL, Nikon Cameras, Forensic Software, Fluorolog, Nikon, filters (435–624 nm)	Clear ridge detail, fluorescence @ 515 nm, strongest minutiae extraction while glass has high contrast via selective filters	High clarity on both fresh and 30-day-old samples. Fluorescence adjusted using filter tuning
	Plastic and Brass Cartridge Case	Good ridge contrast, Case has Partial coverage due to curvature	Plastic: Grade 3–4; 30 minutiae. Case: Grade 2–3; 14 minutiae	Powder Dusting + UV	SEM, UV imaging, Griaule software	Plastic Consistent ridge development, high fluorescence response. The case showed Clear central prints, edge distortion, on curvature	Works well on transparency sheets in the plastic case, while the case has Minor limitations in minutiae due to its cylindrical shape
	Polymer Banknotes	Enhanced Visualisation via filters	Grade 4; 37 minutiae	Multispectral + UV	Crime-lite 8 × 4 MK2, Nikon, Forensic Software	Effective against complex backgrounds (holograms, textures)	Slight glare on holographic foil mitigated by filter selection
Rajan et al. [21]	Metal cans (coloured)	Selective ridge adhesion, strong contrast	Good with curcumin SNP, weak with others	Powder dusting + FALS	FESEM, FTIR, UV–Vis, FALS	Yellow SNP: strong luminescence and thermal stability, 200 nm particles	Curcumin SNPs showed high shelf life (> 1 year)
	Glossy wallpaper/paper box	High clarity and fluorescence with yellow SNP	Excellent for yellow SNP; poor for red/pink	Dusting + UV Imaging	SEM, UV Spectroscopy	Yellow SNP provided the best clarity and contrast	Anthocyanin/carotene pigments degraded under heat
	Patterned leather	Irregular deposition across all powders	Poor across all variants	Powder brushing	FALS, visual inspection	Over-powdering with CFP; SNPs performed poorly due to the texture	Substrate limitations noted
	Plastic bottle/bag	Consistent ridge detection	Yellow SNP is effective, pink/red is less so	Dusting + UV	SEM, UV, FTIR	Curcumin SNPs showed better adhesion than other variants	Carotene extract caused clumping and odour
Rajan et al. [21]	Borosilicate cylinder	Smooth adhesion, clear with yellow SNP	Very good with curcumin-based powder	Powder brushing + UV	FESEM, FTIR, visual comparison	Commercial powder is too intense; over-saturation lowered clarity	Natural dye approach deemed safer and more economical
Bhati et al. [23]	Glass slide and Stainless steel	Adhered to ridges via sweat and oil	Clear Level 1 & 2 patterns, stable for < 30 days. Steel has Clear ridge features, stability up to < 15 days	Brushing + UV (395 nm)	TEM, SEM, FTIR, XRD, UV light, DLS, BET	Ridge patterns and minutiae observed, amorphous silica confirmed, − 27 mV zeta potential. Steel has developed, but it is slightly less durable than glass	Best clarity among all surfaces tested
	Plastic calculator cover and Plastic Phone Case, Silica phone cover	Fine adhesion, some background interference	Visible ridge characteristics, < 20 days durability. Phone case has Clear but minor fading after 15 days, Silica Phone case has excellent clarity, stable up to < 30 days	Brushing + UV (395 nm)	TEM, SEM, FTIR, XRD, UV light, DLS, BET	Pores are visible under UV; reduced sharpness after 2 weeks	Less durable than glass and silica cover, performs best with polymer-based surfaces
	Transparent poly bag	Low contrast due to surface reflection	Not visible	Same	UV Imaging	Failed to develop prints; likely due to light interference	High transparency interfered with UV light reflection
	Porous Surface (Black paper and Paper bag)	Absorption of particles into the substrate	Not visible	Same	Same	Agglomeration and background noise; no ridge detail visible	Unsuitable for porous materials due to nanoparticle absorption
Divya et al. [20]	Glass and Metal (Steel)	Uniform ridge adhesion (SiO₂–4/6). Steel has Strong adherence under UV (SiO₂–6); moderate under light	Excellent (All levels visible). Steel High clarity with SiO₂–6 only	Powder dusting + UV	SEM, XPS, FTIR, UV–Vis, Fluorescence, Nikon SMZ800N, Canon SX30IS	Pt-complex: strong luminescence @ 504–585 nm; ridge patterns visible under UV/white light	Best substrate for both fluorescent and non-fluorescent nanopowders. On steel SiO₂–4 failed due to low colour contrast
	White notebook paper and Black Paper	Absorption reduced visibility for SiO₂–4. on Black paper, High surface contrast under white/UV light	Poor for SiO₂–4; Good with SiO₂–6 (UV), while Black paper was both good	Powder brushing	Optical microscopy under white/UV light	Fluorescent powder resolved minutiae; non-luminescent failed, and Consistent ridge formation on a black background with both powders	Luminescence enabled contrast on a white surface
	Wood	Irregular adhesion with SiO₂–4; Improved with SiO₂–6	Fair for SiO₂–6 only	Dusting + UV	Canon SX30IS, Nikon E200	Moderate fingerprint clarity under UV; non-fluorescent ineffective	Complex texture slightly reduced clarity
Meng et al. [24]	Black plastic bag	Ridge-selective adsorption forms photonic crystals	High clarity under white and 540 nm light	Spray + ethanol rinse	SEM, Zeta Potential Analyser, Nikon D80, Multispectral Light Source	Photonic diffraction visible; SEM confirmed 240 nm size; zeta: narrow dispersion (< 5%)	Most effective under 540 nm light; visual clarity reduced slightly on older (30d) prints
Jenie et al. [22]	Glass, Acrylic, Aluminium and Polyurethane	Glass showed strong ridge adhesion and uniform dispersion. Acrylic had weak particle adherence and medium fluorescence. Aluminium demonstrated good adherence and medium fluorescence. Polyurethane displayed adhesion, although with some agglomeration	Glass offered high clarity in both white and UV light, with the best contrast. Acrylic had low clarity in white light but improved under UV. Aluminium was clear under UV light and moderate under white light. Polyurethane displayed clear ridge details	Powder dusting + UV	TEM, BET, XRD, XRF, FTIR, Fluorescence Spectrometer, Canon EOS 600D	On glass, particles sized 5–10 nm showed 2 × fluorescence intensity over R-6G, with a surface area of 289.2 m2/g. Acrylic surfaces showed visibility only under UV light with minimal powder retention. Aluminium surfaces had medium background interference, but fluorescence improved contrast. Polyurethane surfaces, however, showed agglomeration in TEM images and were visible on the surface	Glass proved to be the most successful, displaying strong ridge detail and visible orange fluorescence. In contrast, acrylic was less suitable due to its surface chemistry. Aluminium showed good clarity, although with minor noise. Polyurethane, while still readable under UV light, was less optimal compared to glass

As opposed to Divya et al., who aimed at synthetic functionalization, Rajan et al. emphasised eco-friendly, bio-based materials without compromising on imaging quality. The process was meant to enhance the clarity of fingerprints on multicoloured or patterned surfaces where traditional powders fail. SNPs (~ 200 nm) were prepared through thermochemical treatment of rice husk ash, alkaline solubilization, and acid precipitation. They were white, spherical particles that were coloured with natural (curcumin, anthocyanin, carotene) and synthetic dyes (safranin O, superb blue, Ponceau 4R), and mixed with corn starch (ideal 9:1 proportion) to enhance pigment dispersal. Characterisation through FESEM affirmed retention of morphology after doping, while FTIR indicated little chemical alteration, manifesting structural stability. Curcumin-doped SNPs exhibited the greatest fluorescence and thermal stability under UV (350–380 nm) light. Latent prints of four donors were made on ten multicoloured, non- and semi-porous surfaces—like metal cans, porcelain, leather, and glossy paper—using squirrel hair brushes and examined under Forensic Alternative Light Source (FALS). Curcumin-doped SNPs provided the highest ridge contrast, adhesion, and shelf-life (more than one year), particularly on non-porous surfaces, compared to synthetic counterparts and minimised problems such as over-powdering and irregular particle sizes encountered with commercial fluorescent powders. Nevertheless, textured leather decreased clarity in all powders. In general, curcumin-derived SNPs were cost-effective, non-toxic, environmentally friendly, and user-safe substitutes for commercial fluorescent powders. Following this environmentally friendly pathway, Jenie et al. [22] further boosted the sustainability and efficiency of fingerprint detection using silica nanoparticles (SiNPs) derived from geothermal wastes and incorporating Rhodamine 6G (R-6G) intra-nanoparticle matrix incorporation. This technology improved fluorescence brightness and lipid residue interaction compared with Rajan et al.'s natural dye-derived system. By converting silica scaling from geothermal power plants—a troublesome industrial byproduct—into a photoluminescent forensic tool, the research provided an inexpensive, non-toxic alternative to traditional powders, solving issues like toxicity, low contrast, and poor surface compatibility. SiNPs were prepared through a sol–gel process: amorphous geothermal silica was treated with different NaOH concentrations (0.375–3.0 N) at 60–90 °C to produce sodium silicate, followed by titration with HCl to give silica gel, which was dried at 80–100 °C. The best nanoparticles (at 1.5 N NaOH, 90 °C) had a BET surface area of 289.2 m²/g, a particle size of ~ 20.7 nm, and mesoporous nature. R-6G was introduced during the sol–gel process, yielding fluorescent silica nanoparticles (FSNPs) of uniform 5–10 nm diameter, as established by TEM. FTIR results established hydrogen bonding between R-6G and silanol groups, while XRF revealed a reduction in SiO₂ purity owing to incorporated dye and salts. XRD established the amorphous character of FSNPs, which enhanced reactivity and fluorescence. Optical analysis revealed FSNPs to exhibit 2.4 times greater fluorescence intensity compared to free R-6G and fluoresce at 583 nm when excited at 553 nm. Their decreased fluorescence lifetime (0.008 ms compared to 0.01 ms) indicated confinement-enhanced emission. Fingerprints from one donor were developed on glass, acrylic, aluminium, and polyurethane. On glass, aluminium, and polyurethane, distinct ridge details were seen under white light, although adhesion on acrylic was weak. Under UV (365 nm), all surfaces exhibited improved clarity and bright orange fluorescence, particularly on glass. FSNPs selectively bound to lipid residues through lipophilic interactions, allowing ridge-specific deposition with little background noise or clumping, even on difficult surfaces such as polyurethane.

Bhati et al. [23] presented mesoporous silica nanoparticles (MSNPs) prepared through a microemulsion templating route (MET), which provided a significantly greater surface area (941.88 m²/g) and better sweat residue adsorption than the lower surface area particles of Divya et al. and Rajan et al. This facilitated high-contrast fingerprint imaging under UV light, particularly on non-porous substrates. MSNPs were a photostable, non-toxic, and highly adsorptive substitute for traditional fingerprint powders, which overcame drawbacks such as low sensitivity, background noise, and toxicity. The nanoparticles were synthesised by a surfactant-templated sol–gel process with CTAB, TEOS, ammonium hydroxide, ethyl acetate, and methanol under controlled conditions. TEM and SEM established the presence of spherical particles (100–150 nm) with deep furrow-like mesopores, a BET surface area of 941.88 m²/g, and a pore volume of 1.30 cm³/g. FTIR, XRD, and EDX established their amorphous nature and chemical integrity, while a zeta potential of − 27 mV established good colloidal stability. MSNPs were tested on five non-porous surfaces—glass slide, stainless steel, plastic calculator cover, plastic phone cover, and silica phone cover—and on porous ones such as paper and wood. Four donors' (post-rubbing forehead and nose) latent prints were developed using a camel hairbrush and viewed with 395 nm UV light. The MSNPs yielded distinct ridge patterns (Level 1) and minutiae (Level 2) on all non-porous surfaces, although sweat pore details (Level 3) were not visible. No useful development was achieved on porous substrates because of nanoparticle absorption and deformation. Prints were stable for as long as 30 days on glass and silica phone covers, but less durable on stainless steel and plastic after 15–20 days. Transparent polybags did not generate useful prints, possibly because of low contrast and high reflectance. Most importantly, MSNPs were found to be non-toxic through MTT assays on Hela and human epithelial cells at concentrations of up to 15 µg/mL, establishing them as safe to use in forensic applications.

Unlike fluorescence-based techniques, Meng et al. [24] created a dye-free technique utilising monodisperse silica nanoparticles (MSNs) to construct photonic crystals for the Visualisation of latent blood fingermarks on dark, non-porous surfaces. The technique overcame issues of dye degradation and background noise inherent in earlier fluorescence methods. The breakthrough involves the use of photonic crystal effects, generated through self-assembled MSNs—to produce visible contrast under white or monochromatic light without chemical tagging. Prepared through the Stöber method, MSNs (~ 240 nm, < 5% size distribution) were dispersed in ethanol with 1.0% Tween 80, creating a stable suspension. Comparative testing revealed that ethanol and Tween 80 provided the best clarity and ridge hold among surfactants and solvents tested. Blood-stained fingerprints, cast onto black polypropylene and aged for up to 30 days, were developed by spraying the MSN suspension, washing with ethanol, and drying. Ridge patterns were made visible by Bragg diffraction, particularly under 540 nm illumination and yellow-green filters. MSNs preferentially attached to ridge residues, creating light-diffracting structures without contaminating furrows, providing high-contrast images even after 30 days, though some sharpness was lost with age. No surface incompatibility was noted, but the process was only tested on black plastic. Notably, it needed no fluorescent dyes or pre-treatment, providing a straightforward, non-toxic, and extremely sensitive method well-suited to quick forensic application, with long-term potential for general surface application. Oliveira et al. [25] pushed fingerprint detection further by synthesising chitosan-functionalized MCM-41 mesoporous silica nanoparticles loaded with dansylglycine (MCM-41@Ch@DnsGly), combining high surface area, intense fluorescence, selective ridge adhesion, and photostability in a single system. These hybrid nanoparticles performed better than previous materials from Divya et al., Bhati et al., and Meng et al., especially on intricate surfaces such as banknotes and metals, and maintained image clarity for aged prints up to 30 days. The nanoparticles were prepared in three steps: MCM-41 formation, chitosan functionalization, and dansylglycine loading, with particles sized between 68 and 113 nm. Fingerprints (fresh and aged) were developed with dusting and subsequent UV lighting, which provided high-contrast images on different surfaces. The particles selectively attached to fingerprint ridges without background noise and clumping due to stable dispersion and photostability. Even on holographic substrates, small glare was reduced by filter adjustment. On the UK Home Office grading scale, 94% of produced prints achieved Grade 3 or 4, demonstrating high identification potential and verifying the system's superior robustness and substrate compatibility for forensic purposes.

Metal oxide nanoparticle for latent fingerprint development

Zinc oxide nanoparticle

Recent developments in the use of zinc oxide (ZnO) nanoparticles for the development of LFP highlight a concerted initiative to leverage ZnO's superior optical, chemical, and biocompatible nature. In a series of studies, scientists have optimised ZnO nanoparticle synthesis, doping, and surface functionalization to transcend conventional fingerprint powder constraints, particularly on non-porous surfaces. The evolution of ZnO nanoparticles for LFP Visualisation has also experienced a tangible and rational advancement in the last few years, from simple nanopowder-based applications to highly engineered, substrate-specific, and eco-friendly materials. Table 4 showed Comparative overview studies employing Zinc oxide nanoparticles for LFP Visualisation.

Table 4.

A Comparative overview studies employing Zinc Oxide nanoparticles for latent fingerprint Visualisation

Study	Surface type	Nanoparticle behavior	Clarity of latent fingerprints	Method used	Instrument(s) used	Results from instruments	Additional observations
Naik et al. [29]	Non-porous: glass, plastic, metal Porous: coin, wood	Spherical/quasi-spherical; good adhesion to ridges, weak on porous	High clarity (Level I–III) on non-porous; poor on porous	Powder dusting + UV	XRD, FESEM, TEM, Raman, CV, PL	Wurtzite structure; 18.57–27.75 nm; oxygen vacancies; PL emissions at 423 & 478 nm; enhanced uric acid detection via voltammetry	Zn₀.₉₅Cu₀.₀₅O found optimal; poor performance on uneven/porous surfaces
Bumbrah et al. [28]	Non-porous: glass, foil, mobile, laptop Porous: not tested	~ 12.8 nm spherical ZnO; blended with talc and crystal violet	Excellent on all non-porous (fresh, wet, aged, depleted)	Powder dusting	XRD, HRTEM, XPS	Pure hexagonal phase; Zn2⁺ oxidation state; adsorbed surface oxygen	Non-toxic, low-cost; no background stain; strong ridge adherence
Verma et al. [27]	Non-porous: glass, copper, ATM Semi-porous: marble Porous: wood	Cone-shaped; large surface area; ~ 85 nm dia., 225 nm height	High clarity on dark/smooth non-porous; moderate on porous	Powder dusting	XRD, FESEM	Hexagonal wurtzite phase; crystallite size ~ 25 nm; selective ridge adherence via van der Waals and hydrogen bonds	High aspect ratio enhanced adhesion; poor performance on wet surfaces
Chandana et al. [30]	Non-porous: foil, glass, plastic, metal Porous: paper	ZN-type ZnO NPs; photoluminescent; 20.42–44.54 nm	Level III details clear under UV (365 nm); weak on wood	Powder dusting + UV	XRD, SEM, TEM, HR-TEM, SAED, PL, UV–Vis DRS	Wurtzite structure; blue emission; high grey values in ridges; best with ZN-based NPs	Fifth depletion prints visible; 24 h print longevity; superior to magnetic powders
Rajan et al. [26]	Non-porous: glass only	~ 13 nm spherical ZnO; white powder for dark backgrounds	Sharp ridge detail on glass; no data for porous	Powder dusting	XRD, UV–Vis, TEM, SAED	Pure hexagonal ZnO; 3.2 eV bandgap; strong ridge adherence due to van der Waals/hydrogen bonding	Ideal for dark surfaces; strong visual contrast; no porous testing
Flores et al. [31]	Non-porous: foil, stainless steel, glass Porous: wood, hard plastic	Precipitation: 17.2 ± 10.8 nm (hemi-spherical) Combustion: 73.4 ± 6 nm (square)	Level I–III on metal/glass; failed on wood; faint on plastic	Powder dusting + UV	XRD, SEM–EDS, TEM, SAED, Raman, PL, UV–Vis	Phase-pure ZnO; green-orange PL; amino acid binding (7 kJ/mol); Zn:O ~ 1.0; better contrast with combustion NPs on black surfaces	Precipitation better for aluminum; combustion better for black glass; poor on porous substrates

Rajan et al. [26] provided the groundwork by synthesising ZnO nanoparticles through a simple direct precipitation route, yielding tiny (~ 13 nm) phase-pure powders that facilitated straightforward, high-contrast fingerprint formation on non-porous surfaces such as dark glass. Though successful in creating visible ridge patterns, this initial process was mostly confined to flat, dark backgrounds and was not surface-versatile or optically tunable. Their application of ZnO as a white contrast powder proved to be highly clear even in the absence of photoluminescence, providing ease for high-contrast Visualisation on black surfaces. Although UV–Vis spectroscopy revealed an absorption maximum at 365 nm and a ~ 3.2 eV bandgap. The nanocrystalline ZnO particles were found to have high surface reactivity, allowing good adhesion to LFP residue through hydrogen bonding and van der Waals interactions. Used as white powder on non-porous glass surfaces, the ZnO NPs gave clear high-contrast ridge definition even before lifting, successfully revealing minutiae without major background staining. Non-porous surfaces alone were tested, with the best performance noted.

Verma et al. [27] reported morphology-controlled ZnO nanostructures, producing cone-shaped nanoparticles of high aspect ratio (~ 85 nm base width and 225 nm height) by chemical precipitation. This breakthrough enhanced fingerprint powder-surface interactions, enabling successful fingerprint development on 12 different substrates, i.e., glass, metal, and plastics. Nonetheless, difficulty still existed for application on wet surfaces and maintaining high clarity on semi-porous surfaces. Through a water-based chemical precipitation process, ZnO nanoparticles were synthesised by mixing ZnCl₂ and NaOH at 90 °C, centrifugation, washing with ethanol, drying at 60 °C, and pulverising. XRD attested a highly crystalline hexagonal wurtzite phase (~ 25 nm crystallite size), whereas FESEM showed cone-shaped structures with an average diameter of ~ 85 nm and height of ~ 225 nm. ZnO powders were tried on 12 substrates, ranging from glass, copper, ATM cards, steel, wood, and marble, covering non-porous, semi-porous, and porous classes. Sustained physicochemical interactions, specifically hydrogen bonding and van der Waals forces with eccrine and sebaceous residues (e.g., amino acids, fatty acids, uric acid), allowed selective ridge adhesion and high-resolution ridge, minutiae, and sweat pore Visualisation. Maximum development was seen on dark, plain non-porous surfaces such as copper and glass, while wood and marble displayed poor to mediocre results owing to low contrast and roughness. Yet, the powder could not be applied on wet surfaces, as too high adhesiveness resulted in smudging. Although photoluminescence was not investigated, the research showed high forensic application of ZnO nanoparticles for dry, clean, non-porous material.

In response to the requirement for field-friendly, practical powders, Bumbrah et al. [28] developed a ZnO nanoparticle-based LFP powder by mixing hydrothermally synthesised nanoparticles with additives like boric acid, talcum powder, and crystal violet. The composite formulation improved adhesion on wet and dry non-porous surfaces and demonstrated outstanding stability for up to 24 h, successfully addressing some of the durability and toxicity issues not specifically addressed in previous research. In comparison to Naik et al., their work focused on affordable formulations that could be applied for practical forensic applications. ZnO nanoparticles were also prepared using a hydrothermal procedure by treating 0.1 M zinc acetate dihydrate with 1 M sodium hydroxide in methanol and subjecting it to autoclaving at 120 °C for 45 min, followed by centrifugation, washing, drying at 60 °C, and grinding. A fingerprint powder was formulated by mixing 2.5 g ZnO with 1 g boric acid and 1 g of talcum powder, 0.45 g barium sulfate, and 0.05 g crystal violet. Characterisation established ~ 12.8 nm spherical nanoparticles with hexagonal structure (XRD), lattice fringes (HRTEM), and surface Zn²⁺ state with adsorbed oxygen (XPS). The method effectively created freshly deposited and aged (up to 24 h) fingerprints on dry and wet non-porous surfaces like aluminium foil, glass, smartphone screens, and laptop touchpads with good ridge clarity and absence of background staining. Depletion experiments indicated good nanoparticle adhesion even to the seventh consecutive impressions. ZnO nanoparticles selectively adsorbed fingerprint ridges through interactions with eccrine and sebaceous constituents such as lipids, amino acids, and uric acid. Even though porous surfaces were not being tested, impressive results on non-porous surfaces established ZnO as appropriate for LFP detection in diverse environments.

Refining the optical properties of ZnO further for forensic imaging applications, Naik et al. [29] synthesised Cu-doped ZnO nanoparticles (Zn_1−xCuₓO), engineering the intrinsic characteristics of ZnO toward visible-range photoluminescence. Their Cu-doped samples had tunable violet-blue emission under UV illumination (423 and 478 nm) and greatly improved visibility of fingerprints on glass, plastic, and metal substrates. This development filled the photoluminescent sensitivity gap for improved detection under forensic UV conditions. This emphasised the necessity of surface affinity optimisation. ZnO's intrinsic non-toxicity, broad bandgap (3.37 eV), and intense UV photoluminescence were improved by Cu²⁺ doping, altering structural, optical, and electrochemical characteristics. Nanoparticles were co-precipitated with zinc acetate dihydrate and copper acetate monohydrate in an ethanol–water medium under ph-controlled NaOH (7–8), and then dried (80 °C) and annealed (500 °C). XRD established a hexagonal wurtzite structure, microstrain, and lattice deformation, crystallite sizes varying between 18.57 and 27.75 nm, which are best at x = 0.05. FESEM and TEM showed spherical to quasi-spherical shapes of nanoparticles (20–35 nm) with limited hexagonal facets. Optical characterisation revealed tunable bandgap (3.37–3.41 eV) and improved visible photoluminescence, producing violet (423 nm) and blue (478 nm) radiation caused by defect states (Zn_i and V_Zn). Raman analysis exhibited oxygen vacancies, whereas cyclic voltammetry reflected increased catalytic activity towards the detection of uric acid, associated with high metabolite interaction in fingerprints. Powder dusting on different substrates (glass, plastic, metal, wood, book covers, and coins), followed by Visualisation with UV light (365 nm) displayed clear high-quality ridge details (Levels I–III) on smooth substrates, but prints on porous materials such as wood and coins were less clear. Improved nanoparticle adhesion to ridges was due to hydrogen bonding and van der Waals interactions with lipids, amino acids, and metabolites in fingerprint residues. Redirecting attention to environmental sustainability, Chandana et al. [30] investigated green combustion synthesis by employing lemon-extracted L-ascorbic acid as a biofuel for the production of ZnO nanoparticles. Their sustainable ZnO NPs exhibited intense blue photoluminescence upon UV (365 nm) illumination and high ridge detail resolution, such as Level III (involving sweat pores and creases) fingerprint features, such as sweat pores and ridge contours. XRD, SEM, TEM, HR-TEM, and UV–Vis DRS established a hexagonal wurtzite structure, with crystallite sizes from 20.42 nm (ZA) to 44.54 nm (ZC). Morphologies were irregular to quasi-spherical, with agglomeration in ZC. In 365 nm UV light, ZnO NPs—particularly Zn-based—exhibited superior contrast and distinct level-III ridge patterns on both porous (paper) and non-porous (glass, plastic, aluminium, metal) backgrounds. Strong interaction with fingerprint residues took place through electrostatic forces and hydrogen bonding. Depletion experiments verified high sensitivity through fifth impressions, and time-dependent tests evidenced maintenance of fingerprint clarity for 24 h when stored on aluminium foil, outperforming normal powders.

Optical complexity was also enhanced by Flores et al. [31], who contrasted ZnO nanoparticles prepared using chemical precipitation and combustion routes. They showed that the size and shape of nanoparticles could be controlled to maximise multiband photoluminescence, allowing Level I to Level III fingerprint features to be captured with better contrast on diverse non-porous substrates such as aluminium, glass, and stainless steel. Precipitation gave smaller hemispherical NPs (~ 17.2 nm), whereas combustion gave larger, uniform square-like NPs (~ 73.4 nm). XRD, Raman, and SAED established phase-pure hexagonal wurtzite ZnO (JCPDS 36–1451), with UV–Vis absorption indicating optical band gaps of 3.69 eV (precipitation) and 3.59 eV (combustion). Photoluminescence investigations indicated strong UV and green-orange emissions, improving fingerprint contrast under 360 nm UV light. NPs preferentially bound to ridge residue via physisorption and chemisorption with biomolecules such as lipids, amino acids, and salts. Excellent ridge detail (Levels I–III) was observed on non-porous surfaces (aluminium, stainless steel, clear and black glass), where precipitation ZnO worked best on metals and combustion ZnO on black glass. Poor performance was obtained on porous surfaces because of absorption of biomolecules.

Iron oxide nanoparticle

Iron Oxide shows a promising result for the LFP development on various surfaces, Table 5 shows the comparative analysis of various studies where iron oxide was used for fingerprint development. Madhavan et al. [32] and Singh et al. [33] both developed iron oxide nanoparticles for LFP Visualisation but used distinct approaches and targeted different advantages. Madhavan et al. focused on an eco-friendly, green synthesis using Camellia sinensis extract, producing Iron Oxide (Fe₂O₃) nanoparticles that showed good ridge detail, particularly on porous surfaces like paper, through van der Waals and hydrogen bonding with fingerprint residues, though performance on non-porous surfaces like glass was comparatively limited. Ferric chloride (0.5 M) was reduced under stirring at 80 °C, followed by centrifugation, washing, and drying at 120 °C to yield unannealed iron oxide (UIO), and further annealing at 450 °C produced crystalline iron oxide (AIO). XRD confirmed rhombohedral Fe₂O₃ with high crystallinity; SEM showed irregular to spherical nanoparticles with uniform distribution; EDAX verified purity. Fingerprints were developed on porous (office paper) and non-porous (glass) surfaces using a synthetic fibre brush. AIO particles offered sharper, clearer ridge details on paper, while prints on glass showed poor contrast, requiring magnification. The nanoparticles interacted primarily with fingerprint ridges through van der Waals forces and hydrogen bonding with residues like amino acids, lipids, and uric acid. Prints on porous surfaces showed better nanoparticle adhesion and clearer minutiae, demonstrating the method’s effectiveness, particularly on fibrous substrates.

Table 5.

A Comparative overview studies employing Iron Oxide nanoparticles for latent fingerprint Visualisation

Study	Surface type	Nanoparticle behavior	Clarity of latent fingerprints	Method used	Instrument(s) used	Results from instruments	Additional observations
Madhavan et al. [32]	Porous: A4 paper Non-porous: glass	Irregular to spherical Fe₂O₃ NPs (UIO & AIO); enhanced crystallinity with annealing	High clarity on porous (paper), sharp ridge detail; lower contrast on glass	Powder dusting	XRD, SEM, EDAX	Rhombohedral Fe₂O₃ phase; high crystallinity (AIO > UIO); elemental purity (Fe, O); homogeneous morphology	AIO performed better than UIO; strong binding to amino acids, lipids, uric acid; hydrogen bonding & van der Waals critical for adhesion
Singh et al. [33]	Porous: paper Non-porous: glass	Spherical, monodispersed γ-Fe₂O₃; mesoporous; magnetically separable	Very high ridge clarity; long-term (3 months) persistence; superior to commercial powders	Powder dusting	XRD, TEM, SAED, BET, VSM, XPS, FTIR, UV–Vis	γ-Fe₂O₃ phase (JCPDS 39–1346, 75–0033); 55–65 nm size; pore size 2–60 nm; surface area 20 m2/g; Fe3⁺ (XPS); Fe–O stretch at 580 cm⁻1; visible light absorption (UV–Vis)	High contrast on both substrates; enhanced interaction via CTAB (quaternary ammonium); magnetically recoverable; no reported limitations

In contrast, Singh et al. engineered mesoporous, magnetically separable γ-Fe₂O₃ nanoparticles via a CTAB-templated co-precipitation and hydrazine reduction method, achieving superior fingerprint clarity, strong adhesion on both porous and non-porous surfaces, and long-term stability up to three months. Their enhanced performance was attributed to electrostatic interactions between surface ammonium groups and anionic components of fingerprint residues. Synthesised via a CTAB-templated co-precipitation method with hydrazine reduction, the nanoparticles were spherical (55–65 nm), mesoporous (pore size 2–60 nm), with 20 m²/g surface area, confirmed by XRD, TEM, SAED, and BET analyses. VSM confirmed ferromagnetism (Ms: 32 emu/g), while XPS and FTIR revealed Fe³⁺ states and CTAB-derived organic functional groups facilitating electrostatic interaction with fingerprint residues (fatty acids, amino acids, uric acid). UV–Vis supported γ-Fe₂O₃ formation. Testing on 50 fingerprints showed superior ridge clarity, contrast, and longevity (up to 3 months) compared to commercial powders, with excellent adhesion and minimal background. Strong electrostatic interactions aided selective adhesion to ridges without limitations on either surface, making the material highly promising for forensic applications.

Copper oxide nanoparticle

Copper oxide nanoparticles have been employed in various studies due to their high versatility and performance across diverse substrates. Table 6 shows the comparative analysis for various methods where copper oxide is used for LFP development. Renuka et al. [34] synthesised a ZrO₂/CuO (Zirconium dioxide/ Copper oxide) nanocomposite using solution combustion to produce multifunctional ZrO₂/CuO nanocomposite oxide (NCO) via solution combustion using zirconyl nitrate, copper nitrate, and oxalyl dihydrazide (ODH) at 500 °C, in Zr: Cu molar ratios of 1:1, 1:2, and 2:1, yielding ZrCu, ZrCu₂, and Zr₂Cu. XRD confirmed crystalline cubic ZrO₂ and monoclinic CuO phases with crystallite sizes of 15.5–19.2 nm, while SEM and TEM showed porous, agglomerated nanoscale morphologies. XPS and FTIR confirmed Zr⁴⁺, Cu²⁺ states, Zr–O/Cu–O bonds, and surface–OH groups, suggesting high surface reactivity. EPR detected Zr³⁺ oxygen vacancies, enhancing electrostatic interactions with fingerprint residues. Zr₂Cu exhibited the best performance for LFP Visualisation on both porous (coloured papers) and non-porous surfaces (glass, marble, stainless steel, aluminium foil, CDs, mouse casing) under 254 nm UV light, producing high-contrast, luminescent ridge details with visible minutiae. PL spectroscopy showed emissions at 435, 482, and 582 nm, supporting strong luminescence; CIE analysis and a high CCT (~ 15,948 K) confirmed intense blue emission, enhancing prints even on dark backgrounds. No surface showed development limitations, with interactions attributed to surface defects and nanoscale adhesion.

Table 6.

A Comparative overview of studies using Copper Oxide nanoparticles for latent fingerprint Visualisation

Reference	Surface type	Nanoparticle behaviour	Clarity of latent fingerprints	Method used	Instrument(s) used	Results from instruments	Additional observations
Renuka et al. [34]	Non-porous: glass, marble, foil, steel, CDs, mouse Porous: coloured papers	NCO (ZrO₂/CuO) nanocomposite; porous and agglomerated; high defect density	Excellent contrast; sharp minutiae; no failure on any surface under UV (254 nm)	Powder dusting + UV	XRD, SEM, TEM, XPS, FTIR, PL, EPR	Dual-phase (cubic ZrO₂, monoclinic CuO); oxygen vacancies (Zr3⁺); PL peaks at 435, 482, 582 nm; CCT ~ 15,948 K	Best response with Zr₂Cu composition; strong luminescence on dark surfaces
Bhagat et al. [35]	Non-porous: glass, steel, butter paper, white paper	Green-synthesised CuO; 500–900 nm spherical; capped with biomolecules from green tea	High-quality ridge details in natural light; no UV needed	Powder dusting	FE-SEM, EDX, FTIR	Cu–O, O–H, CH₂ functional groups; phytogenic residues (C, N, S, Si) provided biomolecule interaction sites	Biocompatible and eco-friendly; strong adhesion; second-level features visible
Atri et al. [36]	Non-porous: glass, foil, tile, steel, CDs, polyethene, spoon Porous: not tested	Rectangular CuO nanosheets; high aspect ratio; ~ 42 nm crystallite size; high surface area (~ 173.4 m2/g)	Sharp ridges; consistent performance across 10 substrates; up to 7th depletion prints clearly	Powder dusting	PXRD, FE-SEM, EDS, FTIR, Raman	Crystalline monoclinic CuO (C2/c); Cu–O at ~ 590 cm⁻1; dislocation density ~ 8.16 × 1014 m⁻2; Raman modes (Ag, Bg)	Strong mechanical interlocking with residues; highly reproducible prints
Dubey et al. [37]	Non-porous: glass, CD, steel Porous: not tested	Nanorods; uniform morphology; ~ 100 nm crystallite size	High-contrast LFPs on glass and steel; moderate clarity on CDs	Powder dusting	XRD, FE-SEM, FTIR	Monoclinic CuO phase; Cu–O peak at 628 cm⁻1; surface–OH and CH groups favourable for adhesion	No background interference; clean ridge Visualisation on smooth substrates
Grover et al. [38]	Non-porous: glass, foil, CD (front/back), bakelite, tile. Porous: paper (failed)	SiO₂/CuO nanocomposite; rod–sphere hybrid morphology; CuO rods (~ 33.68 nm), SiO₂ spheres (~ 506 nm)	Excellent ridge clarity on non-porous; failed on porous (paper); effective post-chemical treatment	Powder dusting	PXRD, FE-SEM, TEM, FTIR	Cu–O and Si–O–Si peaks (~ 480, 530 cm⁻1); strong interfacial bonding; best prints on foil, CD	Chemically stable; works on aged and acid/base-treated prints; effective up to 7th depletion

Bhagat et al. [35] developed a biocompatible CuO nanoparticle synthesis using green tea extract as a reducing agent. This method eliminated the need for toxic chemicals and produced spherical nanoparticles that revealed clear second-level fingerprint features such as bifurcations and deltas on non-porous surfaces like glass and steel. The interaction between nanoparticle surface groups and biomolecules was inferred from FTIR spectra, further advancing the understanding of how CuO nanoparticles adhere to fingerprint residues. The synthesis involved boiling 1 g of dried green tea leaves in 50 mL deionised water at 70–80 °C for 20 min to obtain a phytochemical-rich extract, which was then mixed with 40 mL of 0.05 M CuSO₄·5H₂O and ultrasonicated for 8 h. The resulting dark brown-black colloid, indicating nanoparticle formation, was centrifuged to isolate the product. FE-SEM and EDX showed spherical CuO nanoparticles (500–900 nm) with Cu and O, along with biomolecular residues (C, N, S, Si). FTIR confirmed Cu–O, O–H, and CH₂ bonds, indicating high surface reactivity. The nanoparticles were applied via powder dusting to visualise LFPS on non-porous surfaces (glass, steel, butter paper, white paper). The powder adhered strongly to friction ridges, revealing second-level features such as bifurcations, islands, and deltas, without the need for UV or fluorescent light. Fingerprint residue interaction was facilitated by electrostatic and hydrogen bonding between the nanoparticle surface and biomolecules like amino acids, fatty acids, and uric acid, inferred from FTIR spectra. All tested surfaces showed high-resolution prints with no development failures, demonstrating strong substrate versatility and effectiveness on smooth, non-porous surfaces.

Recent developments by Atri et al. [36] focused on CuO nanosheets, which addressed the limitations of traditional fingerprint powders by providing enhanced surface area and high crystallinity. Their hydrothermally synthesised nanosheets demonstrated superior adhesion and high-resolution fingerprint Visualisation on non-absorbent substrates, including glass and aluminium foil, revealing sharp ridge details even on successive impressions. Using a hydrothermal synthesis approach, CuSO₄·5H₂O was reacted with NaOH under autoclaving at 150 °C for 18 h to produce CuO nanosheets with high crystallinity, enhanced surface area (~ 173.4 m²/g), and uniform morphology. PXRD confirmed the monoclinic CuO phase with an average crystallite size of ~ 42 nm, while FESEM showed rectangular nanosheets with high aspect ratios. EDS indicated a near-stoichiometric Cu:O ratio, and FTIR/Raman analyses identified Cu–O bonds and hydroxyl functionalities, suggesting surface-active sites for fingerprint residue interaction. The nanosheets demonstrated superior adhesion and high-resolution fingerprint development on ten non-porous surfaces (glass, aluminium foil, ceramic tile, etc.), revealing sharp, visible ridge details like bifurcations and deltas, particularly on aluminium foil, glass, and CDs. No performance limitations were observed across the substrates, and the nanoparticle–ridge interaction, attributed to van der Waals and electrostatic forces, was supported by FTIR and Raman results. The nanosheets maintained reproducibility, with clear ridge detail even on the seventh impression. Dubey et al. [37] synthesised copper oxide (CuO) nanoparticles for LFP Visualisation on non-porous surfaces using a cost-effective precipitation method. The synthesis involved dissolving CuCl₂·2H₂O in distilled water, adding glacial acetic acid, and then adjusting pH with NaOH under ultrasonication, resulting in a colour change from blue to black, indicative of CuO formation. The product was centrifuged, washed, and air-dried. XRD confirmed monoclinic CuO with crystallite sizes averaging ~ 100 nm, and FE-SEM revealed uniform nanorod morphology. FTIR identified Cu–O stretching at 628 cm⁻¹, along with surface–OH and CH stretches, indicating surface reactivity. The nanoparticles were evaluated on glass, polycarbonate CDs, and steel using powder dusting. Clear ridge features (bifurcations, ridge endings) were visible on glass and steel, while prints on CDs were fainter due to lower surface moisture. The CuO nanorods interacted with fingerprint residues through electrostatic and hydrogen bonding, particularly with amino acids, lipids, and uric acid. FTIR and FE-SEM confirmed that surface functionalities facilitated this interaction. No background interference or smudging was observed, and porous surfaces were not tested.

Grover et al. [38] developed a silica-coated copper oxide (SiO₂/CuO) nanocomposite for enhanced LFP Visualisation on both fresh and aged non-porous surfaces. The synthesis involved CuO precipitation with copper acetate, CTAB-mediated reduction, and Stöber silica coating, followed by thermal calcination at 400 °C. PXRD confirmed crystalline CuO with a crystallite size of ~ 33.68 nm, and FE-SEM/TEM revealed rod-shaped CuO particles embedded on spherical SiO₂ (506 nm). FTIR analysis showed Cu–O and Si–O–Si stretches at ~ 480 and ~ 530 cm⁻¹, indicating strong bonding. The nanocomposite was tested on various non-porous surfaces (glass, aluminium foil, CDs, bakelite, black ceramic) and paper. It showed excellent ridge adherence and clear second-level features like bifurcations and ridge endings, with the best results on aluminium foil and CDs. It was also effective on aged prints (up to 60 days) and chemically altered fingerprints. However, paper and other porous surfaces showed poor development due to inadequate particle retention. FTIR suggested hydrogen bonding and electrostatic interactions between nanoparticle surface groups (–OH, Cu–O, Si–O–Si) and fingerprint residues like lipids and amino acids, but no specific interaction with uric acid was observed. The material exhibited high reproducibility across successive impressions.

Titanium dioxide nanoparticles

Titanium Dioxide comparative analysis for latent fingerprint development on various surfaces shown in Table 7, with behaviour of nanoparticle on surface and instrument used for characterisation. To begin, Babu et al. [39] reported cerium-doped TiO₂ (Titanium Dioxide) (TiO₂:Ce³⁺) nanophosphors obtained by a solution combustion method, which gave a high photoluminescence under visible light and enhanced physical Visualisation of prints on non-porous and porous surfaces. This was a breakthrough, showing how doping techniques could facilitate ambient-light detection without the need for UV light exposure. Titanium butoxide and cerium nitrate hexahydrate were dissolved in nitric acid and fuels (glycine, ammonium acetate), combusted at 450 °C, and calcined at 700 °C for 2 h. The nanophosphors (25–42 nm crystallite size, 9–30 nm particle size) were spherical. XRD and Raman analysis indicated a phase transition from rutile to mixed anatase-brookite phases by doping. Photoluminescence (PL) analysis showed intense green emission at 544 nm, maximised at 1 mol% Ce³⁺, enhancing print detection. FE-SEM and TEM showed well-dispersed, polycrystalline particles, and UV–Vis DRS showed bandgap increase from 3.10 to 3.23 eV, enhancing excitation by visible light. Fingerprints on porous (paper, currency, cloth) and non-porous (aluminium foil, glass, plastic, ceramic tile) surfaces showed high-contrast ridge patterns, with sharp imaging on non-porous substrates. FTIR ensured active surface groups to provide strong binding to eccrine/amino acid residues. CIE and CCT analysis provided visible emission (coordinates 0.3649, 0.4023; CCT ~ 4563 K; 30% colour purity) to achieve ambient-light Visualisation without using UV. The 1 mol% TiO₂:Ce³⁺ nanophosphors were stable against chemical degradation, did not pose toxicity, and were very efficient for detecting multi-level prints, even from 21-day-old prints.

Table 7.

A Comparative overview of studies using Titanium Dioxide nanoparticles for latent fingerprint Visualisation

Reference	Surface type	Nanoparticle behavior	Clarity of latent fingerprints	Method used	Instrument(s) used	Results from instruments	Additional observations
Babu et al. [39]	Non-porous: aluminium, glass, plastic, tile. Porous: paper, cloth, currency	TiO₂:Ce3⁺ nanophosphors; 9–30 nm spherical; green PL at 544 nm	High clarity across Level I–III features; slight drop on porous surfaces	Powder dusting + white light	XRD, TEM, SEM, Raman, FTIR, PL, UV–Vis, CIE	Anatase/brookite phases; PL optimized at 1 mol% Ce3⁺; bandgap shift 3.10 → 3.23 eV; CCT ~ 4563 K	Stable, visible-light-active, UV-free imaging; print clarity maintained up to 21 days
Yadav et al. [40]	Non-porous: glass, foil, mica, marble. Porous: not primary focus	C-dot@TiO₂ core–shell (~ 500 nm shell); C-dots 2–5 nm; bandgap shift to 3.97 eV	Very high contrast after 7 days submersion; Level III detail on glass and foil	Powder dusting + UV	XRD, TEM, HRTEM, SEM, FTIR, UV–Vis, Raman, EDS	Core–shell structure confirmed; C–O,–OH, amine groups aid adhesion; PL shift via C-dots	Eco-friendly; works underwater; optimal ridge contrast; faint prints on mica; porous surfaces underexplored
Babu et al. [41]	Non-porous: plastic, metal, curved (spray bottle, can) Porous: paper, foil	Flower-like TiO₂:Eu3⁺; 21–32 nm; red PL at 612 nm; multiple morphologies (stem, dumbbell, mushroom)	High-resolution LFPs in 30 s; Level I–III detail; consistent on curved/flat surfaces	Powder dusting + UV (254 nm)	XRD, HRTEM, SEM, TEM, PL, CIE, FTIR	PL peaks intense at 5 mol% Eu3⁺; bandgap ~ 3.2 eV; CCT ~ 2509 K; hydroxyl and amine groups aid adhesion	Strong surface interaction; performance drops at > 5% Eu due to PL quenching
Yang et al. [42]	Non-porous: ITO-glass, plastic, metal. Semi-porous: tape, varnished wood	Electrosprayed TiO₂ aggregates (~ 2 µm); thin film coverage; MALDI matrix functionality	Sharp Level I–III features; chemical maps of TAGs, CEs, FAs; stable aged/fresh prints	Electrospray + MALDI-FTICR MSI	SEM, MALDI-FTICR MSI (9.4 T), MS/MS, image analysis	TAGs, DAGs, and exogenous molecules mapped with high precision; strong ridge adherence via lipophilic binding	Enables donor discrimination via chemical imaging; suitable for aged and fresh LFPs
Hinners & Lee [43]	Non-porous: glass only	Commercial forensic-grade TiO₂ with proprietary additives; high ionisation and adherence properties	Ridge-specific ion maps (e.g., TGs, FAs, WEs); superior to carbon powders	Powder dusting + MALDI-MSI	MALDI-LTQ-Orbitrap, FTMS, UV laser (355 nm)	Signal-to-noise quantification; ion images localised in ridge areas; poor in negative mode with TiO₂ alone	Compatible with low-res MS; non-destructive; additive-based formulation outperforms analytical-grade TiO₂

Yadav et al. [40] prepared a bio-based core–shell nanocomposite (C-dot@TiO₂), with carbon dots from pomegranate peel coated with a TiO₂ shell. Their study expanded the application of TiO₂ to concentrate on surface chemistry to realise persistent fingerprint sensing, even after 7 Days of water submersion, i.e., 7 Days, demonstrating greater environmental stability compared to the previous methods. Carbon dots (C-dots, 2–5 nm) prepared from pomegranate peel extract by hydrothermal treatment (175 °C, 12 h) were shell-coated with TiO₂ with titanium butoxide at 180 °C for 36 h in ethanol–water solvent. The formed nanocomposite was spherical (~ 500 nm shell thickness) with a clear core–shell structure (HRTEM) and anatase TiO₂ phase (XRD, Rietveld refinement). Elemental purity was verified by EDS (Ti, C, O). Bandgap shift from 3.33 eV (TiO₂) to 3.97 eV (C-dot@TiO₂) evidenced higher optical activity, and FTIR identified surface hydroxyl, carboxyl, amine, and C=C groups responsible for the surface reactivity. On both non-porous (aluminium foil, glass) and porous substrates (mica sheet, textured marbles), high-contrast finger printing Visualisation persisted even after the substrate was wetted for 7 days. SEM imaging witnessed strong ridge fixation, revealing Level I–III features (bifurcation, sweat pores, ridge endings, islands). Surface functional groups permitted hydrogen bonding and electrostatic interaction with fingerprint residues (lipids, amino acids). 80–100% prints on aluminium and glass received a "very good" (score 5) rating according to qualitative scoring, with a minor decline in clarity on mica sheets; porous surfaces were not adequately investigated. Characterisation was performed using XRD, TEM, HRTEM, FTIR, UV–Vis DRS, Raman, and SEM, which established structural, morphological, optical, and chemical characteristics of the nanocomposite.

To promote the TiO2 formation, Babu et al. [41] redirected attention towards environmentally friendly synthesis, synthesising europium-doped TiO₂ (TiO₂:Eu³⁺) hierarchical nanostructures through a green hydrothermal route with EGCG as a biosurfactant. The structures showed intense red luminescence under UV illumination and enabled rapid, non-destructive Visualisation of fine ridge details on curved and non-conventional surfaces, thereby extending TiO₂-based materials further into real-world forensic applications. Titanium(IV) isopropoxide and europium nitrate pentahydrate in ethanol, with EGCG, were hydrothermally treated at 100 °C for 6 h and annealed at 600 °C for 3 h. The flower-like nanostructures (dumbbell, stem, mushroom-like) obtained were pH- and EGCG-dependent. XRD established anatase TiO₂ with Eu³⁺ incorporation, crystallite sizes of 21–32 nm (Scherrer) and 20–38 nm (W–H), and HRTEM showed 0.27–0.31 nm interplanar spacing (101 plane). Photoluminescence exhibited intense red emission at 612 nm (⁵D₀ → ⁷F₂) at the peak concentration of 5 mol% Eu³⁺, with CIE coordinates and CCT ~ 2509 K. SEM and TEM established uniform morphology, and FTIR detected O–H, C–O, and N–H groups facilitating ridge adherence through hydrogen bonding and van der Waals forces. Fingerprints developed on plastic, metal, aluminium foil, magazine paper, and curved objects (spray bottles, cans) exhibited distinct Level I–III details (bifurcations, terminations, sweat pores) upon exposure to 254 nm UV light with negligible background noise. Pixel profiling was used to validate selective ridge adhesion, as high Eu³⁺ doping resulted in quenching of the PL quenching. The technique allowed for fast (within 30 s) and non-destructive development on different donors and substrates to make TiO₂:Eu³⁺ nanostructures environmentally friendly, highly luminescent materials for forensic fingerprint analysis.

But until this point, the focus remained largely on physical Visualisation. One of the most significant changes came with Yang et al. [42], who combined electrospray-deposited TiO₂ nanoparticles with matrix-assisted laser desorption/ionisation Fourier-transform ion cyclotron resonance mass spectrometry imaging (MALDI-FTICR MSI). This groundbreaking dual-mode strategy enabled TiO₂ to both act as a fingerprint enhancer and chemical imaging matrix, not just permitting the development of ridge patterns but also molecule-scale detection of endogenous lipids and foreign residues in the prints. TiO₂ NPs (Sigma-Aldrich) were electrosprayed (4 kV, 50 L/h, 1 mm/s) onto LFPs on non-porous substrates (ITO glass, plastic, metal) and semi-porous ones (tape, varnished wood) before vacuum desiccation. SEM validated uniform TiO₂ deposition with ~ 2 µm aggregates. NPs selectively attached to ridges, retaining Level I–III features (arches, bifurcations, pores) without print damage. As enhancer and MALDI matrix, TiO₂ facilitated high-resolution MSI (9.4 T, 1000 Hz, 50 µm raster), imaging lipophilic compounds such as triacylglycerols (TAGs 52:2, 52:3), DAGs, cholesterol esters, and fatty acids, with MS/MS confirmation (Δ ≤ 5 ppm; HMDB, LIPID MAPS). TiO₂ selectively interacted with glycerides and sterol esters through non-covalent forces, and chemical imaging of fresh and 10-day-old prints indicated little loss of signal. High-contrast development was obtained on all substrates tested, porous materials not being tested. TiO₂ retained TAGs better than conventional DHB matrices by inhibiting fragmentation. Further, novel exogenous molecules (e.g., diethylamino hydroxybenzoyl hexyl benzoate, α-tocopherol acetate) provided chemical distinction among overlapping prints and held potential in donor discrimination under forensic analyses.

Hinners and Lee [43] made these advancements more applicable to field use by taking commercially available forensic-grade TiO₂ powders and reusing them as a dual-purpose reagent acceptable for use with lower-resolution MALDI instrumentation. Their work revealed that TiO₂ could obviate the necessity of additional matrix applications while reducing background spectral noise, rendering high-fidelity chemical imaging possible even without the use of high-end laboratory instrumentation. High surface area and photocatalytic stability TiO₂, which was originally used in forensic applications, was redirected to function as a MALDI matrix to eliminate supplementary matrix steps and reduce spectral contamination over carbon forensic powders. Groomed fingerprints were picked up on non-porous glass slides in a split print technique created with TiO₂ or carbon forensic powder (CFP) and examined through MALDI-LTQ-Orbitrap (355 nm Nd: YAG laser, 30,000 resolution at m/z 400, 100 µm raster, 10 shots/pixel, ~ 2700 pixels/condition). Overlay matrices (CHCA, DHB, silver, sodium-gold) were further tried over TiO₂-developed prints. TiO₂ selectively bound to lipid-rich ridge areas and facilitated ionisation of endogenous substances (triacylglycerols, wax esters, fatty acids, cholesterol) and exogenous residues (pseudoephedrine, procaine, personal care products) with low background noise. Particle size was not specifically determined, but forensic-grade TiO₂, augmented with proprietary additives, performed better than analytical-grade TiO₂. Positive ion mode imaging was most effective; negative mode, though, saw TiO₂ without silver sputtering underperforming due to oxygen-rich surface conditions, albeit with improved detection of fatty acids. Development did not destroy structure, retaining details even when under MALDI laser irradiation. Porous surface testing was not conducted, though TiO₂ retained high-contrast fingerprint development on non-porous glass surfaces, affirming its applicability to fast, field-deployable forensic practice.

Conclusion

This review provides an organized and evidence-based integration of the performance of metal and metal oxide nanoparticles in LFP development on different substrates. Of the materials examined, ZnO, CuO, and TiO₂ nanoparticles exhibited superior performance on non-porous substrates, specifically due to their surface energy, morphology-dependent adhesion, and photoluminescent characteristics. Gold nanoparticles (AuNPs) were remarkable for having a double application in visual and chemical imaging, with high selectivity towards amino acid-rich residues, demonstrating impressive success even on problematic porous substrates when functionalized or enhanced with silver. Analogously, silica-based composites exhibited strong adhesion, particularly when designed with high surface area and functional groups optimized for electrostatic and hydrogen bonding interactions. Still, while nanoparticles hold great forensic potential, their use in LFP detection is not without challenges. One of the largest hurdles is the unreliable performance on the porous and textured surfaces of most human skin, with nanoparticle absorption and low ridge contrast being common occurrences. Reproducibility across variable fingerprint age, depletion level, and donor likewise poses issues. Toxicity and environmental hazards associated with nanoparticle exposure, particularly with heavy metal-based or non-biodegradable types, present valid safety concerns. Additionally, there is a dearth of standardized protocols in nanoparticle synthesis, application methods (e.g., dusting vs. sputtering), and imaging conditions, which inhibits practical implementation and regulatory approval. From the forensic practitioner's perspective, material choice needs to be optimized for substrate type and investigation requirements: ZnO and TiO₂ are best suited for high-contrast imaging on non-porous glass and plastic under UV, AuNPs are best suited for dual imaging on porous substrates, and silica or CuO-based composites provide balanced performance on a variety of surfaces with low background interference. The selection of synthesis method (e.g., green synthesis, doping, or hybridization) and application method (e.g., immersion, dusting, or electrospraying) also has direct implications for effectiveness and safety. Although metal and metal oxide nanoparticles offer a revolutionary advantage in LFP detection, making this innovation routine in forensic practice requires more focus on biocompatibility, environmental influence, scalability, and compliance with regulations. Subsequent research must center on creating non-toxic, biodegradable nanoparticles with adjustable surface properties, in addition to universal protocols for cross-laboratory verification. Only through these avenues can nanoparticle-based LFP detection become a standardized and trustworthy tool in the forensic sciences.

Author contributions

Conceptualization, S.T. and M.S.S. Methodology, A.S., M.S.S.; Validation, S.B. and M.S.S; Formal analysis A.A. and A.S.; Investigation, S.T.; Writing—original draft preparation, A.S. Writing—review and editing, visualization. All authors have read and agreed to the published version of the manuscript.

Funding

No specific grant from funding agencies in the public, commercial, or not-for-profit sectors was received for the work.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Ethical approval is not required for the work.

Consent to publish

Not applicable.

Competing interests

The authors declare no competing interests.

Clinical trial number

Not applicable.