Gold nanoparticle based fluorescent aptasensors: A chemical and biological detection perspective

Abstract

Introduction:

In recent decades, the development of simple and reliable techniques for detecting chemical and biological molecules has gained considerable importance. These methods have found extensive applications in different fields, including medicine, biotechnology, food safety, and environmental monitoring. Among these, aptasensors have attracted significant attention owing to their exceptional selectivity, high sensitivity, and versatility in targeting a wide range of analytes. Integrating aptasensors with nanotechnology, particularly gold nanoparticles (Au NPs), has revolutionized the efficiency and performance of these devices. Au NPs, with their unique features like as high surface-to-volume ratio, chemical stability, and extraordinary optical properties, serve as powerful tools for enhancing the aptasensor’s capabilities. These features enable signal amplification, reduction of nonspecific interference, and enhancement of accuracy and sensitivity.

Methods:

This review focuses on recent advances in fluorescent aptasensors amplified by Au NPs. It analyzes the various experiments undertaken to develop and apply these sensors and concludes with a discussion of the technology's future prospects.

Results:

The findings establish the capability of aptamer-Au NP hybrids to detect a broad spectrum of analytes—including mycotoxins, antibiotics, pesticides, heavy metals, and disease biomarkers—with exceptional sensitivity.

Conclusion:

This review emphasizes the powerful potential of aptamer-Au NP hybrids for biosensing applications and suggests a path for future work to move this technology from the lab into practical use.

Introduction

Aptasensors are a type of biosensor that utilize aptamers as recognition elements. These synthetic RNA or DNA oligonucleotides bind specifically to target molecules, enabling highly sensitive and specific diagnostic tests. These sensors are highly useful in environmental and clinical diagnostics for detecting a wide range of analytes, including small molecules, cells, and proteins.¹ Aptamers are usually between 15 and 80 nucleotides in length and are selected from synthetic ssDNA or ssRNA libraries through a procedure named systematic evolution of ligands by exponential enrichment (SELEX). They are synthesized chemically due to several advantages, including cost-effective and convenient synthesis, the possibility of large-scale production with high reproducibility, and their high stability and long shelf life. A key advantage for sensor applications is their ease of modification, which is essential for boosting selectivity, sensitivity, and stability. Additionally, aptamers offer a flexible three-dimensional structure that allows them to specifically bind to a wide range of targets such as cells, proteins, small molecules, and ions. These features provide more advantages over antibodies. However, aptamers have not yet been identified for all analytes, which limits this method.² In the current review and following a previous work,³ we have reviewed the recent developments in gold nanoparticles (Au NPs) based fluorescent aptasensors to sense different chemical and biological molecules. Since aptamers are non-fluorescent compounds, external fluorescent probes must show a fluorescence change upon interaction with targets.

A fluorescence-based aptasensor comprises a target-specific aptamer, a fluorescent probe (e.g., a nanomaterial or organic dye), and often incorporates nanomaterials (e.g. Au NPs) for signal amplification.⁴ Application of Au NPs in amplification of a fluorescent aptasensor can performed in several ways: (i) Fluorescence quenching: Au NPs are mostly modified with aptamer and in the absence of target analytes can quench the fluorescence of nearby fluorophores (fluorescent nanomaterial or organic compound) through mechanisms like the inner filter effect (IFE) and fluorescence resonance energy transfer (FRET). When the target binds to the aptamer, it can cause Au NPs to aggregate, leading to a recovery of fluorophore fluorescence⁵ and (ii) Plasmon enhanced fluorescence: In some designs, the presence of the target and its’s interaction with the aptamer causes a change in the system configuration that provides an ideal fluorophore-nanostructure distance for strong fluorescence enhancement and allowing for sensitive detection.⁶ The mechanism for analyte detection using Au NPs-based fluorescent aptasensors, leveraging the aforementioned role of Au NPs, is as follows: (i) “Turn-on” mechanism: In this mechanism Au NPs quench the fluorescence of a fluorophore through FRET or IFE. In the absence of the target analyte, the aptamer-coated Au NPs remain dispersed, effectively quenching the fluorescence. Target binding induces the release of the aptamer, which triggers the aggregation of the Au NPs and a reduction in quenching, thereby resulting in the recovery of the fluorophore's fluorescence. The increase in fluorescence intensity was proportional to the target analyte concentration. (ii) “Turn-off” or quenching mechanism: Herein, the system uses a double-stranded DNA probe (aptamer + complementary strand) immobilized on nanoparticles. Target binding triggers aptamer release, while nucleases digest unbound strands. The freed aptamer-nanoparticle complexes then quench a fluorophore via FRET of IFE. The quenching of the fluorescence intensity reflects quantitatively target concentration. And (iii) Plasmon enhanced fluorescence: As described in this mechanism, target-aptamer binding induces structural changes that optimize the fluorophore-nanostructure distance. This leads to a significant enhancement of the fluorophore's fluorescence, an effect which is proportional to the target analyte concentration. These mechanisms enable the development of highly sensitive and selective aptasensors for various applications; a selection of these applications is summarized in the following sections.

Applications of Au NPs based fluorescent aptasensors

Au NPs-based fluorescent aptasensors possess unique optical properties and a strong ability to enhance fluorescence signals. This makes them highly versatile for the sensing of diverse compounds. Some notable applications in multiple fields of food safety, environmental monitoring, and health monitoring were summarized and discussed.

Food and environmental samples monitoring

Fluorescence aptasensors have received considerable attention for application in food and environmental monitoring due to their easy operation, fast response, high sensitivity, and potential for point-of-care testing.⁷ Examples of these analytes include:

Bacterium

Salmonella Typhimurium is a foodborne pathogen that persists and spreads readily in the environment, causing substantial global public health issues and widespread bacterial food poisoning.⁸ In a work, Srinivasan et al⁹ present a label-free, fluorescent, aptamer-based method for detecting Salmonella Typhimurium using Au NPs as a quencher and rhodamine B as the fluorophore. The aptamer used in these methods is 5′-ATA GGA GTC ACG ACG ACC AGA AAG TAA TGC CCG GTA GTT ATT CAA AGA TGA GTA GGA AAA GAT ATG TGC GTC TAC CTC TTG ACT AAT-3’. A “turn-on” detection method was employed to identify the bacteria. In this method, FRET between rhodamine B and Au NPs is utilized. The aptamer and Au NPs are mixed with rhodamine B, and its fluorescence is quenched through FRET. The aptamer binds to the surface of Au NPs, preventing aggregation by salt and thus quenching the fluorescence in the presence of Au NPs. When Salmonella Typhimurium is added, it binds to the aptamer, losing the ability to stabilize the Au NPs, allowing salt to induce Au NP aggregation, which results in recovery of the rhodamine B fluorescence. The method had a wide linear range (1530 - 96938 CFU/mL) with a limit of detection (LOD) of 464 CFU/mL. This method is simple, cost-effective, and does not require the labeling of Au NPs or aptamers, making it promising for detecting a wide range of molecules. Another study was conducted by Fu et al¹⁰ and developed a fluorescence aptasensor based on Au NPs and DNA-stabilized silver nanoclusters (DNA-Ag NCs) for Salmonella Typhimurium diagnosisin artificially contaminated milk. Aptamer sequence used was 5’-TATGG CGGCG TCACC CGACG GGGAC TTGAC ATTAT GACAG-3’. The detection mechanism relies on a sandwich structure including magnetic beads conjugated with cDNA1 (biotin-CTGTC ATAAT GTCAA GTCC), the aptamer, and Au NPs conjugated with cDNA2 (GTCGG GTGAC GCCGC CATA-SH). When fluorescent DNA-Ag NCs are added, they are quenched by the Au NPs due to FRET. The presence of Salmonella Typhimurium triggers the specific binding of the aptamer to the bacterial cells, releasing the Au NPs and inhibiting the quenching of DNA-Ag NCs, resulting in increased fluorescence intensity, which serves as the detection signal. The assay has a linear response to Salmonella Typhimurium in the range of 3.7 × 10² to 3.7 × 10⁵ cfu/mL with a LOD of 98 cfu/mL in lab settings and 3.4 × 10² cfu/mL in artificially contaminated milk. The method offers a rapid, sensitive, and specific approach for detecting Salmonella Typhimurium, and the system can be modified to detect other bacteria by replacing the aptamers. This method utilizes DNA-Ag NCs as fluorescent probes due to their desirable properties, including high quantum yield, tunable emission wavelength, excellent photo-stability, biocompatibility, low toxicity, and ultra-small size.

Rapid detection of bacteria like Escherichia coli ATCC 8739 is essential, given its major implications for human health and the safety of food and water supplies. Pathogenic bacteria of E. Coli ATCC 8739, even in very low concentrations, can cause various diseases in humans through food and water contamination. Therefore, new technologies that enable rapid, sensitive detection of pathogenic bacteria are vital for protecting food and water safety. In a study, Jin and colleagues¹¹ used the aptamer sequence GCAAT GGTAC GGTAC TTCCC CATGA GTGTT GTGAA ATGTT GGGAC ACTAG GTGGC ATAGA GCCGC AAAAG TGCAC GCTAC TTTGC TAA-NH2 to detect E. coli ATCC 8739 in upconversion nanoparticles (UCNPs) based FRET aptasensor for diagnosis of E. Coli ATCC 8739 in the pond water, drinking water, and milk. The diagnosis mechanism is based on FRET between UCNPs and Au NPs. Herein, NaYF₄:Yb/Er UCNPs are synthesized via the thermal decomposition method, and their surface is modified with poly(acrylic acid) (PAA) to enhance their dispersibility in water. Subsequently, complementary DNA (SH-TTAGC AAAGT AGCGT GCACT TTTG) is attached to its surface. Au NPs with an average diameter of 13 nm were synthesized employing the citrate reduction method, and thiolated aptamers are attached to their surface. To prepare the FRET sensor, UCNPs conjugated with cDNA are hybridized with Au NPs conjugated with the aptamer to form the FRET pair. The target bacterium, E. coli ATCC 8739, is then introduced into the solution containing the FRET sensor. In the presence of E. coli ATCC 8739, the aptamers bound to the Au NPs bind to the bacterium and detach from the cDNA on the UCNPs. This detachment leads to the recovery of the UCNPs fluorescence intensity, which is proportional to E. Coli ATCC 8739 concentration. This method has a linear range from 5 to 10⁶ cfu/mL with a LOD of 3 cfu/mL.

Mycotoxin

Mycotoxin contamination by Fusarium fungi -such as zearalenone (ZEN) and fumonisin B1 (FB1)- is a primary global food safety concern. ZEN accumulates in the food chain, posing a health risk due to its strong estrogenic properties. According to the European Commission, the tolerable daily intake for this substance is set at 0.25 micrograms per kilogram of body weight.¹² Also, FB1 poses significant health risks to humans and animals, primarily because it interferes with sphingolipid metabolism, leading to various pathological conditions.¹³ Developing rapid and cost-effective methods for detecting these toxins is essential for food safety. Sun and his colleagues¹⁴ used a fluorescent sensor to measure ZEN in cereal products of corn flour and corn oil. The study involved the construction of a “turn-on” fluorescent sensor using a ZEN aptamer sequence (5′-TCATC TATCT ATGGT ACATT ACTAT CTGTA ATGTG ATATA TG-3,), nitrogen-doped carbon dots (N-CDs) and Au NPs as can be seen in Fig. 1. In this system, the N-CDs fluorescence intensity was reduced by dispersed Au NPs due to the inner filter effect (IFE). At the same time, NaCl-induced Au NP aggregates did not quench the fluorescence of the N-CDs. The aptamer could shield Au NPs from aggregation caused by NaCl, but the presence of ZEN diminished this protective capability. According to this principle, the sensor showed a linear response to ZEN concentration of 0.25 to 200 ng/mL and a low LOD of 0.0875 ng/mL. This fluorescent sensor represents a convenient, economical, rapid, and sensitive method to quantify ZEN in complex matrices. In another work, a method was developed for the simultaneous detection of two mycotoxins, ZEN and FB1 in corn samples, reported by He et al.¹⁵ The experimental procedure consisted of several main steps: first, Au NPs and UCNPs were synthesized and surface-modified. Then, the ZEN and FB1 aptamer sequences were attached to UCNPs and Au NPs, respectively. Subsequently, these nanoparticles were linked to each other through complementary DNA (cDNA) sequences, forming core-satellite assemblies of Au NP@UCNP. In a solution lacking ZEN and FB1, UCNPs and Au NPs remain connected through cDNA sequences, and due to the IFE, weak fluorescence responses are received from UCNPs. However, in the presence of ZEN or FB1, the ZEN and FB1 aptamers bind to these mycotoxins, causing the separation of UCNPs from Au NPs, which leads to the recovery of fluorescence signals at 606 nm (for ZEN) and 753 nm (for FB1). The LOD was 0.01 µg/L for ZEN and 0.003 ng/L for FB1, with a linear concentration range of 0.05 to 100 µg/L for ZEN and 0.01 to 100 ng/L for FB1. This method has been used to detect ZEN and FB1 in corn samples. It is recognized as the first report of a fluorescence-based system for the simultaneous detection of two mycotoxins in food products and is considered a suitable option for this purpose.

Fig. 1.

Schematic diagram of the N-CDs/Au NPs “turn-on” fluorescent sensor for determination of ZEN. Reprinted under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).¹⁴

Deoxynivalenol is another mycotoxin produced by Fusarium species, which is toxic to humans and animals. It can cause poisoning, digestive problems, and damage to the immune system.¹⁶ Yu et al¹⁷ reported a dual-mode fluorescence and surface-enhanced Raman scattering (FL-SERS) aptasensor method for the diagnosis of deoxynivalenol in wheat flour. This aptasensor uses Au NPs modified with cDNA as a fluorescence probe, and silver nanoparticles (Ag NPs) modified with a metal-polydopamine (MPDA) framework, which are attached to an aptamer labeled with 6-carboxytetramethylrhodamine (TAMRA), as an SERS probe. The MPDA framework prevents the aggregation of Ag NPs and increases detection sensitivity. Herein, Au NPs are attached to cDNA, and Ag NPs are attached to the aptamer. When deoxynivalenol is not present, the aptamer binds to deoxynivalenol, causing the cDNA to detach from the Au NPs and thus changing the distance between the Au NPs and the Ag NPs. This change in distance leads to an enhancement in fluorescence intensity and an increase in Raman signal intensity proportional to deoxynivalenol concentration. This dual-mode aptasensor showed a linear detection range for deoxynivalenol between 0.1 and 100 ng/mL in both fluorescence and SERS modes, and the detection limit was 0.08 and 0.06 ng/mL, respectively. Employing a dual-mode method improves the accuracy and reliability for detecting deoxynivalenol.

Aflatoxin B1 is another powerful mycotoxin that exhibits hepatotoxic, hepatocarcinogenic, mutagenic, and teratogenic effects, produced by Aspergillus flavus and Aspergillus parasiticus. It forms during the growth of various crops, such as peanuts, corn, other cereals, and oilseeds. This compound is metabolized into aflatoxin M1 and aflatoxin Q1.¹⁸ In a study reported by Wei et al,¹⁹ aflatoxin B1 was measured in corn flour samples by an assay based on a fluorescent aptasensor that employs aflatoxin B1 aptamer (5′-GTTGG GCACG TGTTG TCTCT CTGTG TCTCG TGCCCAAC-3′), Au NPs as a fluorescence quencher and a cDNA labeled with carboxyfluorescein in a hairpin structure (5′-Biotin-GGCAC GAGAC ACAGA GAGAC AACAC GTGCCCAAC-FAM-3′) as a signal probe. Herein, the Au NPs/ carboxyfluorescein-labeled hairpin/aptamer is constructed by initially coating the Au NPs with chitosan and streptavidin, after which the aptamer and labeled DNA are hybridized to form double-stranded DNA that is immobilized on the Au NPs surface via streptavidin. As can be seen in Fig. 2, in the absence of aflatoxin B1, the carboxyfluorescein-labeled in a hairpin structure hybridizes with the aflatoxin B1 aptamer to construct double-stranded DNA, causing the hairpin structure to open so that aflatoxin B1 is positioned away from the Au NPs, leading to strong fluorescence; without aflatoxin B1, the toxin selectively binds to the aptamer, causing the double-stranded DNA to disintegrate, which allows the carboxyfluorescein-labeled to revert to its hairpin structure and bring carboxyfluorescein closer to the Au NPs, where its fluorescence is quenched and the fluorescence intensity decreases, with this change being proportional to the amount of aflatoxin B1 added and thus enabling its quantification. The aptasensor exhibits a LOD of 21.3 pg/mL and a linear range of 0.1 to 10 ng/mL, and key highlights include its high sensitivity for aflatoxin B1 detection, excellent selectivity against high concentrations of interfering toxins, and successful recovery of aflatoxin B1 in corn flour samples with acceptable accuracy.

Fig. 2.

Schematic diagram for the AuNSs/FAM-labeled HP/Apt “turn-off” aptasensor for detection of AFB1. Reproduced from Wei et al¹⁹ with permission from Elsevier (2025).

In another study, Gao et al.²⁰ reported a dual-mode surface-enhanced Raman spectroscopy (SERS)/fluorescence aptasensor for diagnosing aflatoxin B1 in peanut samples. The aptasensor utilizes Au NPs modified with a Raman signal molecule (4-mercaptobenzoic acid, 4-MBA) and a cDNA of an aflatoxin B1 aptamer, along with magnetic nanoparticles modified with a fluorescence signal molecule (Cy5) and the aflatoxin B1 aptamer. Combining these components causes the Au NPs to aggregate on the magnetic nanoparticle surface, forming a satellite-like nanocomposite. This structure enhances the SERS signal but quenches the Cy5 fluorescence due to the close proximity of the Au NPs. Aflatoxin B1 binding induces a conformational change in the aptamer, resulting in the release of the Au NPs from the magnetic nanoparticles. This detachment weakens the SERS signal and recovers the signal of the fluorescence. It works by measuring variations in the SERS signal at 1572 cm⁻¹ and fluorescence intensity at 670 nm. The linear range for aflatoxin B1 detection was from 0.01 ng/mL to 100 ng/mL, with a LOD of 5.81 pg/mL. The dual-signal approach enhances the method's accuracy and reliability. This was demonstrated through effective application to real peanut samples, yielding strong recovery rates between 91.4% and 95.6%.

Ochratoxin A is another mycotoxin found in food products with nephrotoxic, teratogenic, and immunotoxic effects in humans.²¹ In a study reported by Hao et al,²² they focused on developing a fluorescent aptasensor to detect ochratoxin A in the corn samples. Herein, Au NPs modified with DNA tetrahedrons act as the fluorescent acceptors, while Cy5-modified complementary sequences act as fluorescent donors. Ochratoxin A aptamers are embedded within the DNA tetrahedrons and interact with Cy5-modified sequences to facilitate FRET. The DNA tetrahedron helps prevent the aptamers from getting tangled. When ochratoxin A levels increase, they bind more with the aptamers, causing fewer Cy5-modified sequences to bind and less Cy5 fluorescence to be quenched. Consequently, the fluorescence intensity increases with higher ochratoxin A concentration. Under the optimized conditions, the method's signal intensity correlated linearly with ochratoxin A concentration from 0.01 to 10 ng/mL, with a LOD of 0.005 ng/mL. In another study developed by a Taghdisi et al²³ a fluorescent aptasensor are designed with Au NPs and streptavidin-coated silica nanoparticles (SNPs) to detect ochratoxin A in grape juice and serum. The aptamer sequence used was 5’-GATCGG GTGTG GGTGG CGTAA AGGGA GCATCG GACA-Thiol-3’ and its complementary strand sequence was 5’-FAM-AACCC TTTAC GCCAC CCACA CCCGA TCAA-Biotin-3’. The mechanism involves the attachment of the aptamer to Au NPs. Fluorescence quenching occurs when a FAM/biotin-labeled complementary strand binds to this aptamer. In the solution containing ochratoxin A, the aptamer preferentially binds to ochratoxin A, releasing the complementary strand. When the FAM and biotin-labeled CS is constructed and coated with a streptavidin conjugate on the SNPs, the FAM fluorophore is brought into proximity with the SNPs, resulting in enhanced fluorescence. The linear range of the assay was 0.15-6 nmol/L, with a LOD was 0.098 nmol/L for the standard solution, 0.113 nmol/L for grape juice, and 0.152 nmol/L for serum samples. This method demonstrates high sensitivity and selectivity for ochratoxin A detection. It is reproducible with an RSD of less than 8.2%.

Antibiotic

Kanamycin is an aminoglycoside antibiotic effective in treating diseases caused by various microbes and bacteria, including infections caused by E. coli, Proteus, and Staphylococcus. It is widely used as an antibiotic in industrial applications such as animal husbandry, food production, dairy farms, poultry farms, and fish ponds. The prevalence of high stress and unsanitary conditions in industrial farming leads meat producers to rely on antibiotics, including kanamycin, for disease prevention and growth promotion.²⁴ Therefore, testing for antibiotics in water and livestock is essential. In a study reported by Sun et al,²⁵ a fluorescence sensor with a “turn-on” signal mechanism was developed for diagnosing trace kanamycin. This sensor is based on a 5′-FAM-labeled aptamer that serves as the specific binding element and Au NPs that act as a dynamic fluorescence quencher. The proposed method was successfully employed to quantify kanamycin in milk, demonstrating reasonable selectivity and high sensitivity. The aptamer used is (FAM-apt، 5’-FAM-TGGGG GTTGA GGCTA AGCCGA-3’). The mechanism is FREAT between Au NPs and FAM–apt. With the addition of a trace amount of kanamycin, aptamer desorbs from Au NPs and binds specifically to kanamycin. Fluorescence is restored upon the detachment of the FAM group from the Au NP surface. The detection range of kanamycin in this study was reported to be between 0.1 pmol/L and 0.1 mmol/L, with a LOD of 0.1 pmol/L. These results confirm the potential of this fluorescent aptamer-based sensor as an effective tool for monitoring antibiotic residues in food samples. In another study conducted by Li et al²⁶ kanamycin was detected in milk, honey, and serum using a system composed of Au NPs and graphene oxide quantum dots (GOQDs). Herein, a single-stranded DNA (ssDNA) aptamer with high specificity for kanamycin was chosen. When kanamycin is absent, the aptamer adsorbs onto the Au NP surface. This adsorption, driven by interactions between the DNA bases and the gold as well as electrostatic forces, protects the nanoparticles from aggregating in salt solution. Dispersed Au NPs quench GOQD fluorescence through IFE, as a result of the spectral overlap between Au NP absorption and GOQD emission. Following the addition of kanamycin, the aptamer undergoes a conformational change to form a hairpin structure, with kanamycin binding to the aptamer's loop region. This target-aptamer complex exhibits reduced affinity for the Au NP surface, leading to the aggregation of Au NPs under high-salt conditions and subsequent recovery of GOQDs fluorescence. The fluorescence signal of the system is primarily determined by the dispersion state of the Au NPs, which is directly correlated with the concentration of kanamycin. Thus, kanamycin was quantified over a concentration range of 5–600 nmol/L (LOD = 3.6 nmol/L) via fluorescence intensity measurements. This method is limited by its inability to quantify multiple antibiotics simultaneously.

Chloramphenicol is an inexpensive and effective antibiotic with good pharmacokinetic properties, used to control various diseases in animals. However, due to its serious side effects, accurate detection in food and clinical samples is essential.²⁷ In an experiment conducted by Miao et al,²⁸ a fluorescence aptasensor is developed to detect chloramphenicol in seafood samples. They used a thiolated 40-mer aptamer with the following sequence: 5′ (CH2)6-ACT TC AGTGA GTTGT CCCAC GGTCG GCGAG TCGGT GGTAG. Herein, a magnetic probe is prepared by attaching Au magnetic nanoparticle@anti DNA to double-stranded-aptamer-SiO₂@Au NPs (Fig. 3). These nanoparticles consist of double-stranded DNA (aptamer hybridized with its complementary sequence) labeled on the SiO₂@Au composite. When the chloramphenicol and exonuclease I are added to the probe solution, chloramphenicol is captured by the aptamer on the probes. After magnetic separation, single-stranded cApt-SiO₂@Au NPs and the chloramphenicol-aptamer complex are released into the supernatant. Adding the supernatant to the QDs allows SiO₂@Au NPs to effectively quench the fluorescence of CdSe QDs via FRET. This quenching is proportional to the chloramphenicol concentration, exhibiting a linear range from 0.001 to 10 ng/mL. LOD for this method is 0.0002 ng/mL. Herein, exonuclease I, a processive enzyme that digests single-stranded DNA, enhances the method's sensitivity by amplifying the fluorescence signal.

Fig. 3.

Scheme of fluorescence assay based CdSe QD/magnetic SiO₂@Au NPs for chloramphenicol detection. Reprinted from Miao et al²⁸ with permission from Elsevier (2025).

Sulfadiazine is a sulfonamide antibiotic used in livestock to prevent and treat bacterial infections. Its overuse leads to accumulation in animal-derived foods, posing health risks to humans. Sulfadiazine can also contaminate soil and water through animal waste, causing ecotoxicological pollution.²⁹ In a study reported by Yang et al,³⁰ sulfadiazine was determined using a label-free Au NPs based aptasensor in food samples. Herein, in the absence of sulfadiazine, the aptamer with the sequence of 5'-AACCCAATGGGAT-3' adheres to the Au NP surface via non-covalent interactions. The fluorescence of rhodamine B is quenched due to FRET between Au NPs and rhodamine B. In the presence of sulfadiazine, the aptamer binds to it and a high NaCl concentration disrupts the electrostatic balance, causing Au NPs to aggregate. The aggregated Au NPs cannot effectively quench rhodamine B fluorescence, leading to a fluorescence recovery that is proportional to the sulfadiazine concentration. This method showed a linear response in the range of 4-256 ng/mL with an LOD of 2 ng/mL.

Sulfadimethoxine is another sulfonamide antibiotic commonly employed in veterinary medicine, particularly for treating bacterial infections in livestock and poultry. It is effective against many gram-positive and some gram-negative bacteria, and is used to treat animal diseases including coccidiosis, respiratory infections, and enteric conditions. While effective in treating infections, using sulfadimethoxine raises concerns about potential antibiotic resistance and residues in food products, prompting regulations regarding its use in food-producing animals.³¹ In a work conducted by Chen et al,³² they reported the development of an Au NPs based label-free fluorescence-based aptasensor for detecting sulfadimethoxine in water and fish samples. The aptasensor employs an ssDNA aptamer (5’-GAGGG CAACG AGTGT TTATAGA-3’) that specifically binds to sulfadimethoxine, along with CdTe QDs and Au NPs. In the absence of sulfadimethoxine, the aptamer prevents Au NP aggregation, allowing them to quench the fluorescence of CdTe QDs by the IFE process. In the presence of sulfadimethoxine, it binds to the aptamer, causing Au NP aggregation and restoring the QDs’ fluorescence. The linear response range was 10–250 ng/mL, with a LOD of 1.54 ng/mL.

Pesticides

Acetamiprid is a widely used chloronicotinyl insecticide that targets the acetylcholine receptors in insect nerve cells, disrupting their nervous system and causing paralysis and death. It is valued for its broad effectiveness, low dosage, high potency, and long-lasting effects, making it a preferred alternative to urethane and synthetic pyrethroid pesticides. Nevertheless, the extensive application of this pesticide prompts concerns about its environmental impact, particularly its persistence and accumulation in soil.³³ In a work, Yu et al³⁴ validated a sensitive fluorescent aptasensor for quantification of acetamiprid in the traditional Chinese medicinal plant samples. The sensor operates based on FRET between Au NPs and rhodamine B. Upon exposure to acetamiprid, the aptamer forms a complex with the pesticide, detaching from the Au NPs. This detachment enables Au NP aggregation in the presence of high NaCl concentrations, reducing their quenching effect and leading to fluorescence recovery. The fluorescence intensity increases proportionally with acetamiprid concentration, offering a reliable detection signal. The aptasensor demonstrated a linear detection range from 0.1 to 3 mg/mL, with the LOD was 0.0285 mg/mL. Recovery experiments in traditional Chinese medicinal plant samples yielded 96.23% and 105.75%, showcasing the method’s reliability. Another work on acetamiprid monitoring is conducted by Wang et al.⁵ for its detection in vegetable samples using a fluorescent aptasensor based on the IFE between Au NPs and CDs. The specific aptamer used is the S-18 aptamer, with the following nucleotide sequence: 5′-TGTAA TTTGT CTGCA GCGGT TCTTG ATCGC TGACA CCATA TTATG AAGA-3′. In the presence of acetamiprid, the S-18 aptamer preferentially binds to the pesticide molecules, forming complexes. This reduces the amount of free aptamer available to stabilize the Au NPs. As a result, Au NPs aggregate in high-salt environments, resulting in a shift in their absorption spectra. The aggregated Au NPs no longer effectively quench the fluorescence of the CDs. Therefore, the fluorescence of the CDs is restored, and its intensity exhibits a direct correlation with the concentration of acetamiprid. The aptasensor has a linear detection range of 5-100 µg/Land a LOD of 1.08 µg/L. The method can be extended to detect other targets by changing the specific aptamer.

Isocarbophos is an organophosphorus pesticide used on various crops, but it is also toxic, making its detection in food and the environment significant.³⁵ An aptasensor assay based on Au NPs was developed by Wang and colleagues³⁶ for the determination of isocarbophos in vegetable samples. The method employs an ssDNA aptamer with the sequence 5’-AGCTT GCTGC AGCGA TTCTT GATCG CCACA GAGCT-3’, which specifically binds to isocarbophos. Herein, persistent luminescence nanorods are quenched by dispersed Au NPs through the phosphorescence IFE. The binding of isocarbophos to the aptamers on the Au NPs surface induces aggregation. This aggregation reduces the quenching of the nanorods' luminescence, leading to an increase in phosphorescence intensity that is proportional to the isocarbophos concentration. The assay’s linear range and LOD are 5–160 μg/L and 0.54 μg/L, respectively. This method effectively detected isocarbophos in vegetable samples, including Chinese cabbage, brassica rape, and lettuce, with a recovery rate of 96.7% to 106.8%.

Parvalbumin

Parvalbumin is identified as the primary allergen in fish, with 95% of fish allergy sufferers being sensitive to it. Detecting parvalbumin is important as it helps individuals with allergies avoid consuming fish-based foods that may contain this allergen. Allergic reactions to parvalbumin can be severe, including symptoms such as atopic dermatitis, vomiting, urticaria, diarrhea, and even life-threatening anaphylactic shock.³⁷ In a study conducted by Wang et al,³⁸ they utilized a specific aptamer sequence (5′-SH-TTTTT TTTGC CAAAG GAGGC GAGAG ATAAA AGATT GCGAAT CCATT CG-3), selected using the SELEX method, for parvalbumin detection. The designed aptasensor comprises an aptamer attached to Au NPs (Cs1, 5′-SH-TTTTT TTTCG AATGG ATTCG CAA-3′) and complementary strands modified with fluorescent dyes (CS2, 5′-CTCGC CTCCT TTGGC-FAM-3′). The detection mechanism is based on fluorescence changes in the solution containing parvalbumin. The parvalbumin aptamer binds to Au NPs and is then hybridized with a short complementary chain modified on nanoparticles (Au NP-CS1) and a fluorescently labeled complementary chain (FAM-CS2). This assembly forms the aptasensor. When parvalbumin is introduced to the aptasensor, it binds to the aptamer on the Au NPs. This binding causes the Au NPs to detach, thereby releasing the FAM-CS2. The release of FAM-CS2 increases the fluorescence signal as the FRET quenching effect between FAM and Au NPs is eliminated. The linear fluorescence range is 0-40 μg/mL, with a LOD of 0.72 μg/mL and a limit of quantification of 2.38 μg/mL. In this work, parvalbumin was detected in eight different fish species using the developed aptasensor.

Abscisic acid

Abscisic acid is a key phytohormone that regulates plant growth and mediates adaptive responses to abiotic stress.³⁹ In a work reported by Shi et al,⁴⁰ an Au NP-mediated ratiometric fluorescence aptasensor was utilized to detect abscisic acid in rice seeds. The aptamer with the sequence ‘5–SH–GCGGA TGAAG ACTGG TGTGA GGGGA TGGGT TAGGT GGAGG TGGTT was used in this study. This mechanism operates on the principle that CQDs@ZIF-8 acts as a fluorophore with two emission wavelengths (Fig. 4). Apt-Au NPs cause fluorescence quenching of CQDs@ZIF-8 at 490 nm and enhance it at 657 nm. Upon addition of abscisic acid, this molecule binds to Apt-Au NPs and causes their aggregation. This aggregation reduces the energy transfer between CQDs@ZIF-8 and Apt-Au NPs. As a result, the fluorescence intensity increases at 490 nm and decreases at 657 nm. The LOD of this method is 30.0 ng/L, and its linear range falls within 0.100-150 ng/mL.

Fig. 4.

A schematic diagram of the CQDs@ZIF-8/Apt-Au NPs ratiometric probe for detecting abscisic acid in rice seeds. Reprinted from Shi et al⁴⁰ with permission from Elsevier (2025).

Urea

The importance of urea detection is twofold: to combat economically motivated adulteration (e.g., adding urea to milk to increase its apparent protein and solid-not-fat levels) and to protect consumers from the associated health risks. High levels of urea can cause indigestion, renal failure, and even cancer.⁴¹ In a study conducted by Kumar et al,⁴² urea in milk samples was detected using a non-enzymatic method based on unmodified Au NPs. The specific DNA aptamer used in this study was selected through the FluMag-SELEX method and is named U38, with a full length of 80 bp including forward and reverse primer regions. The random DNA library sequence used was 5’-GTCTT GACTA GTTAC GCC-N40-TCATT CAGTT GGCGC CTC-3’. The forward primer (DrF) sequence was 5’-FITC-GTCTT GACTAGT-TACGCC-3’ and the reverse primer (DrR) sequence was 5’-GAGGC GCCAA CTGAA TGrA-3’. By using fluorescent FITC-labeled aptamer, in the absence of urea, its fluorescence is quenched by Au NP-mediated energy transfer. When urea is added, the aptamers dissociate from the Au NPs, restoring the fluorescence. The aptasensor exhibits a linear response within a urea concentration range of 20 to 150 mmol/L, and a LOD of 20 mmol/L.

17b-Estradiol

17b-Estradiol is a potent estrogenic compound among natural steroid estrogens. Its detection is crucial because of its misuse in the food industry and its potential to cause hormonal imbalances in the human body. Excess 17b-estradiol can lead to various health problems, including obesity, diabetes, cardiovascular diseases, and cancer.⁴³ Qian et al⁴⁴ develop a CDs and Au NPs based FRET aptasensor for detecting 17b-estradiol in sea salt samples. The nucleotide sequence of the 17b-estradiol aptamer used in this study is 5′-AAGGG ATGCC GTTTG GGCCC AAGTT CGGCA TAGTG-3′. CDs were modified with an amino-modified oligonucleotide (F1), and Au NPs were modified with a thiol-modified oligonucleotide (F2). The 17b-estradiol aptamer hybridized with F1 and F2, bringing CDs and Au NPs into close proximity, thus enabling the FRET phenomenon. When 17β-estradiol was introduced, it bound to the aptamer, which led to the disassembly of the CD-F1-Apt-F2-Au NP complex. The separation of CDs and Au NPs disrupted FRET, resulting in the fluorescence of the CDs to “turn-on”. A positive correlation was observed between the fluorescence intensity and 17β-estradiol concentration over the range from 400 pmol/L to 5.5 µmol/L. The LOD of the experiment was found to be 245 pmol/L.

Bisphenol A

Bisphenol A, a widely used industrial compound, is a known endocrine disruptor with harmful effects at very low exposure levels.⁴⁵ In a study, Wang et al⁴⁶ reported a fluorometric aptasensor relied on Au NPs and N-doped CDs for the detection of bisphenol A in environmental tap water samples. The aptamer sequence used in this experiment is 5′-CCGGT GGGTG GTCAG GTGGG ATAGC GTTCC GCGTA TGGCC CAGCG CATCA CGGGT TCGCA CCA-3′. The detection mechanism relies on the IFE of Au NPs on the fluorescence of N-doped CDs. The presence of bisphenol A triggers its binding to the surface-bound aptamers, resulting in Au NP aggregation. This diminishes the IFE and consequently restores the fluorescence of the N-doped CDs. This increased fluorescence signal is then measured to indicate the concentration of bisphenol A. The linear rang of this method is between 10 to 250 nmol/L and 250 to 900 nmol/L, and the LOD is 3.3 nmol/L.

Ions

Mercury ions bioaccumulate through the food chain and pose significant risks to human health upon exposure. As a result, many countries have imposed strict limits on mercury levels in food products.⁴⁷ In a study for mercury ion monitoring based on aptasensor, Liu et al.⁴⁸ utilized two aptamer sequences 5′ NH₂ C₆-CTACA GTTTC ACCTT TTCCC CCGTT TTGGT GTTT-3′ and 5′ SH C6-GAA ACT GTA G-3′. This detection strategy utilizes FRET between UCNPs and Au NPs. In the lack of mercury ions, the long aptamer binds to UCNPs and the short aptamer binds to Au NPs, forming a hybrid structure. This leads to FRET between UCNPs and Au NPs, which quenches the fluorescence of UCNPs. The presence of mercury ions induces the formation of a loop structure in the long aptamer, facilitated by strong interactions between mercury ions and thymine. This structural change releases Au NPs from UCNPs, reducing FRET and restoring the fluorescence of UCNPs. The sensor’s linear range is 0.2–20 µmol/L, with a LOD of 60 nmol/L. They used this technique for the quantification of mercury ions in milk samples with good precision. A similar method is developed by Jia et al⁴⁹ for quantifying lead ions in the spinach standard substances. This method is based on FRET between graphite phase carbon nitride nanosheets (g-CNNs) as a fluorescence donor and Au NPs as a fluorescence acceptor. Initially, a specific lead aptamer, with the sequence 5′-NH₂-(CH₂)₆-GGGTG GGTGG GTGGGT-3′, is attached to the surface of g-CNNs. Then, Au NPs attach to the aptamer-g-CNNs complex, quenching the fluorescence of g-CNNs. In the presence of lead ions, the aptamer binds to lead and detaches from the Au NPs, restoring the fluorescence of g-CNNs. The linear range of this sensor is between 0 and 1000 μg/mL with a LOD of 0.8 μg/mL.

Cadmium (II)can cause severe harm to human health, including kidney and reproductive disorders, Itai-itai disease, and osteoporosis. Long-term exposure to low doses of cadmium (II) can also increase the risk of cancer.⁵⁰ In an experiment, Li and his colleagues⁵¹ used a fluorescent aptasensor to detect cadmium (II) in water, soil and vegetable samples. The nucleotide sequence of the aptamer used in this experiment is: 5’-AGTGA CGTGC TGGAC TCCGG ACTAT TGTGG TATGA TCTGG TTGTG ACTAT GCAGT GCGTG CA-(CH2)3-SH-3’. This aptasensor uses Au NPs as one of the key components. Au NPs are combined with sulfur (S) and nitrogen (N)-doped CQD and act as fluorophores. Next, a molecularly imprinted polymer (MIP) is formed on the SN-CQD/Au/aptamer-cadmium complex. After removing cadmium (II) from the MIP, the recognition sites for cadmium (II) remain in the aptamer and MIP. The binding of cadmium (II) ions to the aptamer-MIP results in the quenching of the SN-CQD/Au fluorescence. The linear range of the sensor response is linear in the concentration range of 20 pmol/L to 12 nmol/L. Furthermore, the LOD of this sensor is 1.2 pmol/L. This experiment is based on dual recognition (aptamer and MIP) to increase the sensor’s selectivity, and the use of SN-CQD/Au as a highly sensitive fluorescence element. Recovery rates for cadmium (II) in irrigation water, surface water, industrial wastewater, agricultural soils, and vegetables (e.g., pak choi) were satisfactory, ranging from 82.1% to 113.9%.

Health monitoring

Biomarker of diseases

Interleukin-6 (IL-6) is a multifunctional cytokine implicated in numerous autoimmune diseases, including inflammatory bowel disease, rheumatoid arthritis, and glomerulonephritis. The detection of IL-6 is crucial as it is a prognostic indicator for infections, including COVID-19 and immune system-induced acute lung injury in COVID-19 patients. Additionally, the ability to detect this molecular biomarker rapidly and with high sensitivity in minimal samples is crucial for enabling early cancer diagnosis and guiding effective treatment strategies. In healthy adults, IL-6 levels in biological fluids range between 5 and 25 pg/mL, whereas abnormal levels up to 1000 pg/mL may indicate serious health issues such as chronic infections or various cancers.⁵² In a study conducted by Mahani et al,⁵³ two single-stranded DNA aptamer sequences was used for IL-6 detection: SH-CTTCC AACGC TCGTA TTGTC AGTCT TTAGT-3′ and SH-(CH2)6-TGGTG GATGG CGCAG TCGGC GACAA-3. The detection mechanism, as in previous reports, is based on FRET between N-CDs (donors) and Au NPs (quenchers). The aptamer exhibits high-affinity binding toward IL-6 when the cytokine is present, causing a structural change in the probe and the detachment of N-CDs from Au NPs and the restoration of N-CD fluorescence, which is proportional to IL-6 concentration range of 1.5 to 5.9 pg/mL with a LOD of 0.82 pg/mL (at S/N = 3). In this study, IL-6 is effectively detected in human serum samples. However, the limitations of this work include its inefficiency in detecting IL-6 in patients with severe sepsis (concentrations above 500 pg/mL) and the interference of UV absorbers, which can weaken the signal. In related work based on a similar principle, Wu et al⁵⁴ developed a multicolor fluorescent aptasensor using Au NPs to classify breast cancer via the subtype biomarkers HER2 and ER. Fluorescently labeled (TAMRA dye) aptamers specific to ER and HER2 breast cancer subtype biomarkers are attached to the surface of Au NPs. The fluorescence is reduced in this state (Fig. 5). Upon binding to the target biomarker protein, the fluorescently labeled aptamer produces a recovered fluorescence signal that is specific to a particular breast cancer subtype, thereby facilitating quantitative classification.

Fig. 5.

A Schematic of classification of breast cancer by an Au NPs-based multicolor fluorescent aptasensor. (A) Probe synthesis and (B) diagnosis procedures. Reprinted from Wu et al⁵⁴ with permission from Elsevier (2025).

Salivary lysozyme serves as a valuable biomarker for assessing various health conditions and physiological states. It is an enzyme with antimicrobial properties found in saliva, playing an essential role in the body’s first line of defence against pathogens. Its levels can reflect the immune status of an individual and are influenced by factors such as stress, infections, and inflammatory diseases. Measuring salivary lysozyme can thus provide insights into oral health, systemic diseases, and even emotional or psychological stress, making it a non-invasive tool for diagnosing and monitoring of health conditions.⁵⁵ A work conducted by Pereira-Barros et al⁵⁶ developed an aptamer-based fluorescence biosensor for salivary lysozyme detection. The platform utilizes plasmonic metal-enhanced fluorescence from ZnSSe alloyed QDs and Au NPs, employing lysozyme as a model analyte for real-world saliva screening. As can be seen from Fig. 6, the 60-mer ssDNA anti-lysozyme aptamer, with the sequence 5′SH-AGCAG CACAG AGGTC AGATG GCAGG TAAGC AGGCG GCTCA CAAAA CCATT CGCAT GCGGC-3′, was immobilized on L-cysteine ZnSSe QDs. The bonding of citrate-capped Au NPs to the aptamer-functionalized QDs formed the Apt-ZnSSe-QDs-Au NP fluorescence biosensor probe. Detection is achieved through affinity-based binding between the aptamer and lysozyme. This binding event induces a localized surface plasmon resonance (LSPR) signal from the Au NPs, resulting in amplified fluorescence from the QDs. Under optimum conditions, salivary lysozyme was quantitatively detected with a LOD of 22.9 μg/mL and a linear detection range of 0.05–3 mg/mL; the biosensor probe’s selectivity was further demonstrated by testing potential interfering enzymes, including human salivary α-amylase, aspergillus-derived β-galactosidase, and aspergillus-derived amyloglucosidase, with the assay showing high selectivity for lysozyme recognition.

Fig. 6.

Illustration of detection mechanism of salivary lysozyme using the Apt-ZnSSe-QDs-AuNP aptasensor. Reprinted from Pereira-Barros et al⁵⁶ with permission from Elsevier (2025).

Protein

Plasmodium falciparum lactate dehydrogenase (PfLDH) is a protein that plays a significant role in malaria detection. It is an enzyme found in the red blood cells of individuals infected with malaria, at nanomolar concentrations, and is also present in the blood serum at picomolar levels. The detection of PfLDH is crucial for diagnosing malaria, with the gold standard methods being microscopic examination of the parasite and polymerase chain reaction (PCR). Nevertheless, such methods are often time-consuming and necessitate access to advanced laboratory facilities as well as specialized technical expertise. Therefore, simple devices like biosensors have gained attention for on-site testing and mass screening. Minopoli et al⁶ used a plasmon-enhanced fluorescence-based apta-immunosensor to detect PfLDH protein in whole blood. This sensor was fabricated by electrostatically self-assembling Au NPs randomly on a glass substrate, using 5-carboxyfluorescein (5-FAM) as the fluorophore. The sensor employs a sandwich assay format for detection. A receptor layer of antibodies is covalently immobilized on the Au NPs, followed by a top layer of 5-FAM-labeled aptamers that bind the captured analyte. The sandwich configuration ensures high target specificity while maintaining an ideal fluorophore-nanostructure separation of approximately 10–15 nanometers, enabling strong fluorescence enhancement. The detection is based on plasmon-enhanced fluorescence, where resonant coupling between the metal nanoparticle plasmon and the nearby fluorophore enhances excitation and emission. Results showed that this biosensor can specifically detect PfLDH in whole blood at concentrations as low as 10 pmol/L (0.3 ng/mL) without any sample pre-treatment. The sensor has a dynamic range of five decades and a LOD of 10 pmol/L. Advantages of this sensor include its scalable design, high analytical capability, and no need for sample pre-treatment.

Alpha-fetoprotein (AFP) is a 70-kDa glycoprotein naturally produced in the fetal liver and in tiny amounts in adults, whose increased levels in the blood of adults can indicate hepatocellular carcinoma (HCC). It may also be elevated in other conditions such as germ cell tumors, chronic liver diseases, and pregnancy.⁵⁷ In a study conducted by Zhu et al⁵⁸ employed a DNA aptamer with the nucleotide sequence 5′-NH2-GGCAG GAAGA CAAAC AAGCT TGGCG GCGGG AAGGT GTTTA AATTC CCGGG TCTGC GTGGT CTGTG GTGCT GT-3′ for the specific diagnosis of AFP in serum samples. The experimental method is based on a fluorescence aptasensor that utilizes FRET between AFP aptamer-labeled luminescent CdTe QDs and Au NPs. Herein, the AFP aptamer probe was constructed by first labeling CdTe QDs with the AFP aptamer and then attaching them to SiO₂ nanoparticles. Subsequently, anti-AFP antibody-functionalized Au NPs were prepared by conjugating the antibodies to the gold nanoparticles. The presence of AFP brings the QDs and Au NPs into proximity via a specific aptamer-target-antibody complex, quenching the CdTe QD fluorescence through FRET. The quantitative measurement of this fluorescence decrease correlates with the AFP concentration (Fig. 7). Furthermore, the SiO₂ nanoparticles serve to prevent QD aggregation and increase assay sensitivity. The LOD of this fluorescence aptasensor for AFP is 400 pg/mL with a linear concentration range of 0.5 to 45 ng/mL, and this method shows great promise for point-of-care and on-site screening for hepatocellular carcinoma.

Fig. 7.

Schematic illustration of the CdTe QDs/Au NPs aptasensor for the diagnosis of AFP. Reprinted from Zhou et al⁵⁸ with permission from Elsevier (2025).

Drug

Dopamine is an important neurotransmitter that plays a key role in regulating the central nervous, renal, hormonal, and cardiovascular systems. Variations in its levels are associated with mental disorders such as depression, addiction, and schizophrenia. Dopamine deficiency can lead to Parkinson’s disease. Additionally, dopamine is illegally added to animal feed as an adrenergic stimulant to enhance muscle mass. However, residues in animal products can lead to foodborne illness. Therefore, using dopamine in animal feed is prohibited in many countries, and preventing its illegal addition is essential.⁵⁹ In a study conducted by Xu et al,⁶⁰ a 58-mer DNA aptamer (5'-GTCTC TGTGT GCGCC AGAGA ACACT GGGGC AGATA TGGGC CAGCA CAGAA TGAGG CCC-3')-based sensing strategy is used for dopamine diagnosis. As in previous reports, the detection method is based on FRET between rhodamine B and Au NPs. When Au NPs are dispersed, they can quench rhodamine B fluorescence via FRET, but upon aggregation, FRET efficiency decreases, resulting in the recovery of rhodamine B fluorescence. This method operates within a linear range of 26 to 2.90 × 10^-3 nmol/L, with a LOD of 2 nmol/L.

Cocaine is a highly addictive stimulant derived from the coca plant, which represents one of the most serious cases of substance abuse worldwide. Chronic abuse of this drug may result in serious adverse health outcomes, including hypertension, tachycardia, anxiety, organ failure, cardiac arrest, and heightened susceptibility to human immunodeficiency virus infection.⁶¹ Therefore, rapid and easy detection of cocaine is essential to prevent these adverse effects. In a study, Emrani et al.⁶² utilized aptamer (5′- CCATA GGGAG ACAAG GATAA ATCCT TCAAT GAAGT GGGTC TCCC -Thiol-3′), FAM-labaled complementary strand of aptamer (5′-FAM-ATTGA AGGAT TTATC CTTGT CTCCC TATGC TTCAAT-Biotin-3′), and two kinds of nanoparticles of silica nanoparticles (SNPs) coated with streptavidin and Au NPs for cocaine detection in the serum samples. In the absence of cocaine, FAM remains close to the surface of Au NPs, causing a dim fluorescent signal. However, target binding induces a hairpin structure in the aptamer's complementary strand, bringing the FAM fluorophore closer to the SNP surface and significantly increasing fluorescence emission. The developed fluorescent aptasensor demonstrated excellent selectivity for cocaine, achieving a LOD as low as 209 pmol/L in aqueous solution and 293 pmol/L in serum samples.

Digoxin, classified as a cardiac glycoside, is commonly prescribed to treat heart conditions like atrial fibrillation and congestive heart failure. The therapeutic range of digoxin is 0.5–2.0 mg/L, and plasma concentrations above this range can lead to toxic effects.⁶³ To ensure effective treatment while minimizing the risk of concentration-dependent toxicity, digoxin therapy requires monitoring of plasma levels with a selective and sensitive method. Shirati et al⁶⁴ detailed a novel nanobiosensor based on aptamer/Au NPs/polyvinyl alcohol (PVA) hydrogel for digoxin detection in plasma samples. The aptamer sequence used was 5′-AGCGA GGGCG GTGTC CAACA GCGGT TTTTT CACGA GGAGG TTGGC GGTGG-3′. This biosensor operates on a fluorescence "off-on" strategy (Fig. 8). The PVA hydrogel acts as the fluorescent probe. In the initial state, aptamer-functionalized Au NPs quench the hydrogel's fluorescence by acting as energy receptors. Introduction of the digoxin target promotes the formation of an aptamer-digoxin complex, which desorbs from the Au NP surface. This compromises the nanoparticle stability, resulting in salt-induced aggregation and restoring the fluorescent signal. The linear range of this biosensor is 10–1000 ng/L, with a LOD of 2.9 ng/L. The significance of this work lies in the novel application of the PVA/Au NPs pair as a fluoroprobe. This is the first report utilizing this pair in a fluorescence "off-on" strategy for constructing a highly selective and sensitive nanobiosensor.

Fig. 8.

Schematic illustration of aptamer/AuNPs/PVA nanobiosensor for detection of digoxin. Reprinted from Shirani et al⁶⁴ with permission from Elsevier (2025).

Staphylococcus aureus

Staphylococcus aureus is responsible for one out of every five infections following surgery and trauma and can cause skin infections, wounds, and serious diseases such as pneumonia, endocarditis, arthritis, abscesses, and osteomyelitis. Additionally, S. aureus can secrete seven types of toxins known as staphylococcal enterotoxins, which are responsible for food poisoning. This bacterium inhabits diverse environments—including dust, water, milk, and air—and is also a natural commensal, found on the skin and in the noses of about 25% of healthy individuals and animals. It is usually harmless but can cause foodborne illness by producing toxins and other pathogenic compounds when ingested.⁶⁵ In a study, Pebdeni et al⁶⁶ used the fluorescent “turn-on” aptasensor with aptamer sequence 5′-GCGCC CTCTC ACGTG GCACT CAGAG TGCCG GAAGT TCTGC GTTAT-3′ to detect S. aureus in human serum. The detection mechanism in this study is based on FRET between CQDs as a donor and Au NPs as an acceptor. In this system, the specific binding of the aptamer to S. aureus causes the detachment of Au NPs from the CQD-aptamer complex, thereby restoring the fluorescence intensity of the CQDs. The concentration of S. aureus can be quantified by measuring the fluorescence signal of the supernatant. The linear range of this assay is from 10⁸ to 10¹ CFU/mL, with a LOD of 10 CFU/mL. The CQDs were synthesized from the natural and cost-effective source of olive leaves.

The analytical performance of each reported method is also tabulated in Table 1.

Table 1. Characteristics of included studies on Au NPs- based fluorescent aptasensors .

Analyte	Sensor	Sample	Linear range	Detection limit	Ref.
Food and environmental samples monitoring
Salmonella Typhimurium	Apt/Au NPs/rhodamine B	-	1530 - 96938 CFU/mL	464 CFU/mL	9
Salmonella Typhimurium	Apt/DNA-Ag NCs/Au NPs	Milk	3.7 × 102 - 3.7 × 105 cfu/mL	3.4 × 102 cfu/mL	10
E. Coli ATCC 8739	Apt/Au NPs/NaYF4:Yb/Er UCNPs	Pond water, Drinking water,Milk	5 - 106 cfu/mL	3 cfu/mL	11
ZEN	Apt/Au NPs/N-CDs	Corn flour Corn oil	0.25 - 200 ng/mL	0.0875 ng/mL	14
ZEN FB1	Au NP/Apt/UCNP	Corn samples	0.05 - 100 µg/L 0.01 - 100 ng/L	0.01 µg/L 0.003 ng/L	15
Deoxynivalenol	Au NPs modified with cDNA/Ag NPs modified with MPDA/aptamer labeled with TAMRA	Wheat flour	0.1 - 100 ng/mL	0.06 ng/mL	17
Aflatoxin B1	Au NPs/ carboxyfluorescein-labeled hairpin/Apt	Corn flour	0.1 - 10 ng/mL	21.3 pg/mL	19
Aflatoxin B1	Au NPs modified with 4- MBA and a cDNA of an aflatoxin B1 Apt/magnetic nanoparticles modified with Cy5 and the aflatoxin B1 Apt	Peanut samples	0.01 ng/mL - 100 ng/mL	5.81 pg/mL	20
Ochratoxin A	Au NPs modified with DNA tetrahedrons /Cy5-modified complementary sequences	Corn samples	0.01 - 10 ng/mL	0.005 ng/mL	22
Ochratoxin A	Au NPs and streptavidin-coated SNPs	Grape juice Serum	0.15-6 nmol/L	0.113 nmol/L 0.152 nmol/L	23
Kanamycin	5′-FAM-labeled aptamer/Au NPs	Milk	0.1 pmol/L - 0.1 mmol/L	0.1 pmol/L	25
Kanamycin	Au NPs/GOQDs/ssDNA aptamer	Milk Honey Serum	5 - 600 nmol/L	3.6 nmol/L	26
Chloramphenicol exonuclease I	Au magnetic NPs@anti DNA/double-stranded-aptamer-SiO2@Au NPs/ CdSe QD	Seafood samples	0.001 - 10 ng/mL	0.0002 ng/mL	28
Sulfadiazine	Apt-Au NPs/rhodamine B	Food samples	4-256 ng mL-1	2 ng mL-1	30
Sulfadimethoxine	ssDNA aptamer-Au NPs	Water Fish	10–250 ng/mL	1.54 ng/mL	32
Acetamiprid	Apt-Au NPs/rhodamine B	traditional Chinese medicinal plant samples	0.1 - 3 mg mL−1	0.0285 mg mL−1	34
Acetamiprid	Apt/ Au NPs/CDs.	Vegetable samples	5-100 µg/L	1.08 µg/L	5
Isocarbophos	ssDNA Apt/luminescence nanorods/Au NPs	Vegetable samples	5–160 μg/L	0.54 μg/L	36
Parvalbumin	Apt-Au NPs-CS1/FAM-CS2	Fish species	0-40 μg/mL	0.72 μg/mL	38
Abscisic acid	Apt-Au NPs/CQDs@ZIF-8	Rice seeds	0.100-150 ng/mL	30.0 ng/L	40
Urea	FITC-labeled aptamers/Au NP	Milk	20 - 150 mmol/L	20 mmol/L	42
17b-Estradiol	CD-F1/AptF2-Au NP	Sea salt samples	400 pmol/L - 5.5 µmol/L	245 pmol/L	44
Bisphenol A	Apt- Au NPs/N-doped CDs	Tap water	10 - 250 nmol/L 250 - 900 nmol/L	3.3 nmol/L	46
Mercury	Apt-Au NPs/UCNPs	Milk	0.2–20 µmol/L	60 nmol/L	48
Lead	Apt/g-CNNs/Au NPs	Spinach standard substances	0 - 1000 μg/mL	0.8 μg/mL	49
Cadmium	MIP/SN-CQD/Au NPs/ Apt	Water, Soil,Vegetable samples	20 pmol/L - 12 nmol/L	1.2 pmol/L	51
Health monitoring
IL-6	Apt/ N-CDs/Au NPs	Serum	1.5 - 5.9 pg/mL	0.82 pg/mL	53
ER and HER2	Apt/Au NPs/TAMRA dye	-	-	-	54
Salivary lysozyme	Apt/ZnSSe alloyed QDs and Au NPs	Saliva	0.05–3 mg/mL	22.9 μg/mL	56
PfLDH	Au NPs/5-FAM-labeled Apt	Whole blood	-	10 pmol/L	6
AFP	Apt/CdTe QDs/Au NPs	Serum	0.5 - 45 ng/mL	400 pg/mL	58
Dopamine	Apt/Au NPs/rhodamine B	-	26 - 2.90 × 10-3 nmol/L	2 nmol/L	60
Cocaine	FAM-labaled Apt/SNPs coated with streptavidin/Au NPs	Serum			62
Digoxin	Apt/Au NPs/PVA	Plasma	10–1000 ng/L	2.9 ng/L	64
S. aureus	CQDs as a donor and Au NPs	Serum	108 - 101 CFU/mL	10 CFU/mL	66

Limitations of Au NPs based fluorescent aptasensors

Despite their high sensitivity and versatility, Au NP-based fluorescent aptasensors face several limitations that hinder their widespread practical application. A primary challenge is the stability of aptamers and nanoparticles under varying environmental conditions (e.g., pH, ionic strength) also remains a concern, affecting reproducibility. Additionally, the cost and time involved in aptamer selection (SELEX) and sensor fabrication can be prohibitive. Furthermore, most reported sensors are designed for single-analyte detection, lacking multiplexing capability. Real-sample validation is often insufficient, and long-term stability studies are rare. Finally, the quantitative performance may be compromised by fluorophore photobleaching or aggregation-induced signal variability. Addressing these limitations through material engineering, multiplex assay design, and robust validation is essential for future translation beyond laboratory prototypes.

Future research directions

To address the limitations of Au NP-based fluorescent aptasensors, future research should focus on enhancing multiplex detection capabilities to enable simultaneous analysis of multiple analytes, which is essential for real-world applications like food safety screening or clinical diagnostics. Improving the stability and reproducibility of aptasensors in complex matrices requires the development of more robust surface modifications and shielding strategies. Efforts should also be made to simplify sensor design and instrumentation to facilitate point-of-use testing, potentially through integration with portable readers or smartphone-based detection platforms. Exploring new nanomaterials could increase sensitivity and reduce background interference. Finally, rigorous validation using real samples and long-term stability studies, along with cost-effective manufacturing methods, will be essential to transition these promising biosensors from laboratory prototypes to commercially viable products.

Conclusion

This study reviewed recent advances in Au NP-based fluorescent aptasensors, focusing on their design principles, detection mechanisms, and diverse applications in food safety, environmental monitoring, and medical diagnostics. Our goal was to provide an overview of how integrating aptamers with the unique optical properties of Au NPs—such as fluorescence quenching (via FRET or IFE) and signal amplification—has enabled the development of highly sensitive, selective, and rapid biosensors. The results demonstrated that these aptasensors can detect a wide range of analytes, including mycotoxins, antibiotics, pesticides, heavy metals, and disease biomarkers, with exceptionally low detection limits. In general, this review underscores the transformative potential of aptamer-Au NP hybrids in biosensing and outlines a roadmap for future innovation to bridge the gap between scientific discovery and real-world application.

Review Highlights

What is the current knowledge?

• Aptasensors offer a high sensitivity and selectivity, making them valuable for medical diagnostics, food safety, and environmental monitoring.

• Integration of Au NPs enhances aptasensor performance.

• Au NPs provide high surface-to-volume ratio, stability, and optical properties, reducing interference and boosting sensitivity.

• Demonstrated success in food safety, environmental monitoring, and clinical diagnostics highlights their versatility and reliability.

What is new here?

• This review examines recent advances in Au NP-based fluorescent aptasensors, focusing on their design, mechanisms, and applications in detection.

• These biosensors detect diverse analytes, including mycotoxins, antibiotics, pesticides, heavy metals, and biomarkers, with ultra-low detection limits.

• Further research is needed to bridge lab-scale innovations with real-world applications, ensuring scalability and commercial viability.

Competing Interests

The authors declare that they have no competing interests.

Data Availability Statement

Data supporting this study are included within the article

Declaration of AI-assisted Tools in the Writing Procedure

The authors declare that Generative AI was used in the creation of this manuscript. During the preparation of this work the authors used DeepSeek in order to improve the writing process and to enhance the readability and language of the manuscript. After using this tool/service, the authors reviewed and edited the content as needed and takes full responsibility for the content of the published article.

Ethical Approval

Not applicable.

Funding Statement

This work was supported by the Research Affairs of Tabriz University of Medical Sciences (Tabriz, Iran) under the grant number 73561.