Study and Evaluation of Zn_0.2Co_0.8Fe₂O₄ Nanocrystalline Spinel Ferrites for Antimicrobial and Anticancer Applications

Abstract

Zinc-added cobalt ferrite with a composition of Zn_0.2Co_0.8Fe₂O₄ was synthesized using the sol–gel method with poly­(vinyl alcohol) as a chelating agent. The structural properties of the as-synthesized ferrite were determined using X-ray diffraction and Fourier transform infrared spectroscopy (FTIR). The measured structural parameters revealed the formation of a single-phase cubic spinel structure in the sample. Various structural parameters were measured to identify the variations upon the addition of Zn²⁺. The surface of the sample was coated with SiO₂ and NH₂ to achieve better catalytic performance. The surface coating of the sample was confirmed using FTIR and energy-dispersive X-ray analysis (EDAX). The optical energy gap of the sample was calculated using a Tauc plot derived from the UV–vis spectra, and the Urbach energy of the sample was calculated. The bandgap energy and Urbach energy were determined to be 2.14 and 0.04 eV, respectively. This confirmed the semiconducting nature of the sample. Thermogravimetric analysis was performed using differential scanning calorimetry. Surface morphology and elemental analyses were performed using field-emission scanning electron microscopy (FESEM) with EDAX. The almost uniform size of the particles confirmed the effectiveness of the synthesis method. The direct-current electrical conductivity was measured using the two-probe method, and the dielectric properties were measured using an impedance analyzer in the frequency range of 100 Hz–10 MHz. The variations in the dielectric properties are also discussed in this study. The proposed cation distribution was confirmed using Mössbauer spectroscopy. Magnetic measurements were performed using a vibrating sample magnetometer, and the obtained magnetization (37.16 emu/g) and coercivity (0.209 Oe) confirmed the soft ferromagnetic nature of the Zn-added Co ferrite. The antibacterial and antifungal activities of Zn_0.2Co_0.8Fe₂O₄ against Escherichia coli and Aspergillus niger were evaluated. These findings suggest that Zn_0.2Co_0.8Fe₂O₄ nanoparticles have potential applications in biomedicine, such as in magnetic hyperthermia treatment and drug delivery systems.

1. Introduction

Over the past few decades, nanotechnology has expanded in the field of biomedicine by bridging the physical, chemical, and biological sciences. Primarily, this development is based on nanoparticles, which have outstanding physical and chemical properties, including a large surface area relative to volume, adjustable optical and magnetic properties, and improved catalytic effectiveness. Their nanoscale size allows these features to be used in tailored drug delivery systems and diagnostic instruments. Magnetic nanoparticles made from ferrites have garnered significant attention in biomedical research because of their unique magnetic properties, simple preparation techniques, and capacity for functionalization for specific applications. Ferrites are magnetic ceramics composed of iron oxide and other metallic components. These materials exhibit unique properties, such as high electrical resistance, low eddy current losses, and improved chemical durability, making them ideal for use in electronics and biomedicine. − Among these, spinel ferrites (AB₂O₄) are the most important magnetic materials for several technical and biological applications due to their structural stability and magnetic tunability. − Spinel ferrites have varying magnetic properties, ranging from superparamagnetic to ferromagnetic, and they depend on the cation distribution over the A and B sites. Doping with elements such as Ni²⁺, Mg²⁺, Mn²⁺, Zn²⁺, and Co²⁺ improves the superparamagnetic properties and biocompatibility for biomedical applications. MnFe₂O₄ and CoFe₂O₄ are functionalized spinels used most often in magnetic hyperthermia, which efficiently produces localized heat to destroy cancer cells in the presence of an alternating magnetic field. Spinel ferrites have been studied for drug delivery to reduce side effects and improve efficacy by using their magnetic properties to facilitate the targeted distribution of medicinal medications. Among these spinel ferrites, CoFe₂O₄ is a magnetic material widely used in many biomedical applications because of its exceptional magnetocrystalline anisotropy, high coercivity, strong magnetization, and high chemical stability. , The properties of ferrite materials depend completely on the preparation method and sintering temperature. Among the various synthesis methods, sol–gel, coprecipitation, and hydrothermal methods provide precise control over the particle size and shape of ferrite materials. These preparation methods enhance the coercivity and magnetocrystalline anisotropy of cobalt ferrite, making it suitable for magnetic hyperthermia and data storage applications. Among the various techniques, the sol–gel autocombustion method is the most promising for synthesizing homogeneous nanoparticles, offering superior control over the stoichiometry at relatively low temperatures. , This control is crucial for tailoring the magnetic, electrical, and biomedical properties of nanoparticles. Furthermore, the addition of PVA facilitated the uniform dispersion of metal ions within the precursor, resulting in the production of smaller particles. In cancer treatment, magnetic hyperthermia therapy significantly depends on the concentration of cobalt-ferrite. This method selectively kills malignant cells while protecting healthy cells using cobalt ferrite nanoparticles to create focused heat when subjected to an alternating magnetic field. Many studies have shown that changing the size, shape, and surface coating of nanoparticles greatly increases heating efficacy and lowers cell toxicity, thereby improving therapeutic results. Moreover, cobalt nanostructures limit the growth of harmful bacteria by generating reactive oxygen species and perturbing bacterial membranes. − Broad cobalt ferrite applications can be used to develop nanofluidic technologies. Moreover, cobalt nano ferrites have been used in electroosmotic flow systems, particularly for heat transfer in medical equipment and drug delivery.

Zinc ferrite is essential for developing drug delivery systems. Zn²⁺ ions incorporated into the spinel structure of cobalt ferrite generate a synergistic effect between the magnetic properties and biocompatibility of Zn. , This results in lower magnetic anisotropy and coercivity while preserving or increasing the saturation magnetization, making it more suitable for biological applications such as magnetic hyperthermia, drug delivery, and imaging. The preference of cations at the A and B sites and the diamagnetic nature of Zn²⁺ ions regulate their magnetic properties. These regulated magnetic properties, with the addition of Zn²⁺ ions, are suitable for drug delivery and MRI contrast applications. Ferrite nanoparticles are increasingly used in medical device coatings and antimicrobial dressings, serving as antibacterial agents that inhibit tissue recovery. Moreover, the substitution of Zn creates surface imperfections and enhances the presence of redox-active Fe³⁺ sites, which greatly improve antibacterial, antifungal, and cytotoxic effects, demonstrating its superior biological performance compared to CoFe₂O₄.

Functional groups designed for particular purposes are attached as an organic molecule layer surrounding the core. , The surface is modified with 3-aminopropyltriethoxysilane (APTES) to introduce reactive amine groups on the surface of the nanoparticles. The effective capture of the target depends entirely on the functionalization of the nano ferrites. Silane agents are often suggested as a possibility for directly modifying the surface of magnetic nanoparticles. According to the Arkles method the physicochemical mechanism of silane agent alteration on the surface of magnetic nanoparticles. The hydroxyl groups on the magnetic nanoparticle surface react with the methoxy groups of the silane molecules, leading to the formation of Si–O bonds. Kachi et al. reported that the silane present on the surface of the magnetite core was found to have basic amino and hydroxyl groups attached to its outer layer, which can be utilized in numerous technological applications, particularly in various biological processes.

Studies on Gram-positive and Gram-negative bacteria, including multidrug-resistant types, have shown their effectiveness. Given the advantages of zinc-doped cobalt ferrites, 20% zinc substitution in the cobalt ferrite matrix (Zn_0.2Co_0.8Fe₂O₄) was chosen to examine its structural and magnetic properties for potential biomedical applications. We chose Zn_0.2Co_0.8Fe₂O₄ because of its good mix of structural, magnetic, electrical, and biological features. This mixture works well because Zn²⁺ makes it safe for the body and improves its magnetic qualities, whereas Co²⁺ adds magnetic strength and stability. This makes it useful for medical applications, such as heating therapy, targeted drug delivery, and germ-killing coatings. It also works well in the industry for applications such as sensors and high-frequency electronics because of its excellent electrical performance and heat stability. The many uses of this mixture, as shown through detailed tests, make it a top choice for both medical and industrial purposes.

2. Synthesis and Experimental Techniques

Zn_0.2Co_0.8Fe₂O₄ nanoparticles were synthesized using the sol–gel method. The synthesis employed iron­(III) nitrate nonahydrate (Fe­(NO₃)₃·9H₂O), cobalt­(II) nitrate hexahydrate (Co­(NO₃)₂·6H₂O), and zinc nitrate hexahydrate (Zn­(NO₃)₂·6H₂O) as the raw materials. Poly­(vinyl alcohol) (PVA) was used as the chelating agent, and deionized water was used as the solvent for the synthesis. PVA acted as a fuel agent and enhanced the reaction rate of the combustion reaction. The procedure commenced with the dissolution of appropriate quantities of metal nitrates in a minimum amount of deionized water according to the stoichiometric ratio of Zn_0.2Co_0.8Fe₂O₄. The mixture was agitated with a magnetic stirrer at temperatures between 60 and 90 °C to produce a homogeneous solution from the completely dissolved nitrates. The solution was agitated for 15–20 min at 60 °C to ensure complete mixing and equal fuel distribution, followed by the addition of PVA in a 1:1 molar ratio to the total metal nitrates. A thick gel was developed when PVA interacted with the metal nitrates when the solution was heated to 120 °C. When PVA and nitrates were blended for the synthesis of ferrite nanopowders at this temperature, the gel spontaneously ignited and produced high-temperature sparks. Following ignition, the porous spongy material was allowed to cool to ambient temperature, thoroughly desiccated to remove any residual moisture, and subsequently ground into a fine powder using a mortar and pestle. A schematic of the synthesis of Zn_0.2Co_0.8Fe₂O₄ is presented in Figure . A small quantity of powder was collected, and 5% PVA was incorporated into the particles. Disk-shaped pellets (3 mm thick and 10 mm in diameter) were fabricated using a hydraulic pressure of 5 t/inch to evaluate their electrical properties. Highly porous samples were sintered at 900 °C for 4 h. At this temperature, the organic residues from the sol–gel process were completely broken down, and the supplied energy was adequate to encourage the development of a single-phase cubic spinel structure. For electrical characterization, annealing at 900 °C is essential to achieve an ideal balance between the structural integrity and nanoscale features. Subsequently, silver paste was applied to both surfaces to establish the ohmic contacts.

1.

Schematic diagram of the synthesis of Zn_0.2Co_0.8Fe₂O₄.

X-ray diffraction (XRD) was performed using a Bruker AXS D8 Discover X-ray diffractometer at a wavelength of 1.5406 Å with a step size of 0.02° and an angular resolution of ±0.01°. The Fourier transform infrared (FTIR) spectra of the sample covering 500–4000 cm^–1 were obtained using a PerkinElmer Spectrum Two instrument with KBr pellets. The optical characteristics were investigated using a Hitachi U-4100 UV–vis spectrophotometer. Field-emission scanning electron microscopy (FESEM) with a TESCAN MIRA microscope was used to examine the surface morphology. FESEM imaging was conducted at 100.0k× magnification with a resolution of 1 nm using a 20 kV accelerating voltage. An LCR meter (Newton 4th Ltd.) operating from 100 Hz to 10 MHz with a frequency resolution of 1 Hz and an accuracy within ± 0.2% was used to investigate the electrical and dielectric features. The magnetic characteristics were measured using a vibrating sample magnetometer (VSM) (Lakeshore 7400) with a field range of ±3 kOe. The Mössbauer spectrum of the sample was recorded using a Mössbauer spectrometer operated in the constant-acceleration mode (triangular wave) in transmission geometry at room temperature. The source employed was Co-57 in a Rh matrix with a strength of 50 mCi. The velocity scale was calibrated using an enriched α-⁵⁷Fe foil. The line width (inner) of the calibration spectrum was 0.25 mms^–1. The isomer shift (δ) values were relative to those of an Fe metal foil (δ = 0.0 mm/s).

2.1. Surface Coating

Surface coating was performed by adding 0.5 g of NPs to cyclohexene (10 mL of cyclohexene and 1.5 mL of IGEPAL CO-520) in a round-bottom flask and stirring for 20 min. Subsequently, 2 mL of ammonia solution was added, and a transparent emulsion was obtained by closing the vessel and sonicating it for 20 min. Subsequently, tetraethyl orthosilicate (TEOS) (200 μL) was added dropwise to the solution, and the solution was stirred for 2 days at a speed of 800 rps. SiO₂-coated NPs were then obtained. However, to functionalize with the NH₂ group, 1 mL of APTES was added dropwise to the prepared SiO₂-coated NPs solution, and the mixture was stirred for an additional 2 days. Next, NPs coated with NH₂-functionalized SiO₂ were precipitated by adding acetone, washed four times with ethanol, and then stored in H₂O. An illustration of the surface coating of the Zn_0.2Co_0.8Fe₂O₄ sample is shown in Figure .

2.

Surface coating illustration of Zn_0.2Co_0.8Fe₂O₄.

2.2. Cell Viability Assay

The MTT assay was performed on MCF-10A and MCF-7 cells to evaluate the in vitro cytotoxicity of Zn_0.2Co_0.8Fe₂O₄ and Zn_0.2Co_0.8Fe₂O₄@SiO₂-NH₂ nanoparticles. MCF-10A is an epithelial nontumorigenic cell line derived from a healthy mammary gland, whereas MCF-7 is an estrogen receptor-positive breast cancer cell line. Both cell lines were procured from NCCS and maintained at 37 °C in a 5% CO₂ incubator with DMEM complete media supplemented with 10% FBS, 1% Pen-Strep, and 1% Glutamax (Thermo Scientific, Gibco). 90% confluent cells were then trypsinized with trypsin-EDTA (Gibco) and plated in 96 well plates. The cells were allowed to adhere for at least 24 h, the medium was replaced, and the nanoparticles dissolved in 1X PBS were added at increased concentrations (0, 100, 200, 300, 400, 500, and 1000 μg/mL). The plate was incubated for 24 h, the media were discarded, the wells was washed, and 100 μL of 50 μg/mL MTT (Sigma-Aldrich) was added to each well and further incubated for 4 h at 37 °C. After incubation, the medium was discarded, 200 μL of DMSO (Sigma-Aldrich) was added, and the absorbance was measured at 590 nm. The readings were tabulated in MS Excel, and the percentage of viable cells was calculated using the following formula:

$$\%\mathrm{of}\mathrm{viable}\mathrm{cells}=\frac{\mathrm{OD}\mathrm{of}\mathrm{control}-\mathrm{OD}\mathrm{of}\mathrm{test}}{\mathrm{OD}\mathrm{of}\mathrm{control}}\times 100$$ 1

3. Results and Discussion

3.1. XRD Studies

The X-ray diffraction (XRD) patterns of the nanocrystalline Zn²⁺-doped cobalt ferrite are shown in Figure . The image reveals a single-phase cubic spinel structure, aligned with the standard JCPDS data (00-003-0864). Figure shows the XRD pattern of Zn_0.2Co_0.8Fe₂O₄ obtained via Rietveld refinement. This refining technique successfully indexed nearly all the diffraction peaks to a cubic crystal structure with an Fd3̅m space group. The detailed structural properties derived from this refinement are presented in Table . The FullProf Rietveld refinement method was employed for peak analysis and indexing, yielding a strong correlation between the fit and the estimated data. The presence of diffraction peaks corresponding to the (220), (311), (222), (400), (422), (333), (440), (620), and (533) planes indicates that the Zn_0.2Co_0.8Fe₂O₄ nanoparticles exhibited a single-phase nature. The Rietveld analysis revealed that the Zn_0.2Co_0.8Fe₂O₄ sample 100% exhibited a single-phase cubic structure. Moreover, the absence of extraneous peaks or phases in the refinement graph of the sample, as demonstrated by the Rietveld refinement, confirmed the successful synthesis of Zn_0.2Co_0.8Fe₂O₄.

3.

XRD patterns of Zn_0.2Co_0.8Fe₂O₄.

1. Various Structural Parameters of Zn_0.2Co_0.8Fe₂O₄ .

parameter	value	parameter	value	parameter	value	parameter	value
aexp (Å)	8.3899	P (%)	28.30	dBL (Å)	2.0648	d (Å)	3.6329
ath (Å)	8.4119	LA (Å)	2.9574	dBEU (Å)	2.9670	e (Å)	5.4494
V (Å3)	590.57	LB (Å)	3.6328	p (Å)	2.0633	f (Å)	5.1377
χ2	1.071	U3m (Å)	0.2541	q (Å)	1.8757	θ1 (deg)	123.9774
GoF	2.752	U43m (Å)	0.3790	r (Å)	3.5916	θ2 (deg)	147.8102
d311 (nm)	10.11	dAE (Å)	3.0602	s (Å)	3.6527	θ3 (deg)	91.9313
ρX (g/cm3)	5.315	dAL (Å)	1.8740	b (Å)	2.9663	θ4 (deg)	125.7306
ρB (g/cm3)	3.810	dBE (Å)	2.8724	c (Å)	3.4783	θ5 (deg)	76.1894

A standard relationship (eq ) was employed to determine the lattice parameter a of Zn_0.2Co_0.8Fe₂O₄:

$$a=d\sqrt{h^2+k^2+l^2}$$ 2

where d is the interplanar spacing and (hkl) are the Miller indices. Table summarizes the calculated structural parameters of Zn_0.2Co_0.8Fe₂O₄. The Nelson–Riley function was used to extend the lattice parameter values obtained from the individual peaks to obtain the correct lattice constant. The obtained lattice parameter value agreed with those reported previously. ,, The structural properties and cation distribution in spinel ferrites between tetrahedral (A) and octahedral (B) sites are significantly affected by the ionic radii of the cations, which in turn determine the lattice parameter. In Zn_0.2Co_0.8Fe₂O₄, the substitution of Zn²⁺ in place of Co²⁺ results in notable changes to the lattice parameter, which is attributed to the larger ionic radius of Zn²⁺ (0.74 Å) compared to that of Co²⁺ (0.65 Å). Accurate theoretical calculation of the lattice parameter is crucial for comprehending cation redistribution in the A and B sites, as these redistributions influence the magnetic and structural properties of the material. In the Zn_0.2Co_0.8Fe₂O₄ spinel structure, Zn²⁺ and Fe³⁺ were found at both the A and B sites, whereas Co²⁺ showed a strong preference for the B sites. The site preferences of ions are influenced by their size and electronic configuration, which consequently affect cation distribution. The approximate distribution of cations at sites A and B is as follows: (Zn_0.1Fe_0.9)­[Zn_0.1Co_0.8Fe_1.1]­O₄. From the proposed cation distribution, the lattice parameter (a _th) was calculated using eq :

$${\mathit{a}}_{\mathrm{th}}=\frac{8}{3\sqrt{3}}[({\mathit{r}}_{\mathrm{A}}+{\mathit{r}}_{\mathrm{O}})+\sqrt{3}({\mathit{r}}_{\mathrm{B}}+{\mathit{r}}_{\mathrm{O}})]$$ 3

where r _A and r _B are the radii of the cations at the A and B sites, respectively, and r _O is the radius of the oxygen atom. The calculated a _th values are listed in Table . The values of r _A and r _B were calculated using the formulas shown in eq :

$$\begin{array}{l}{\mathit{r}}_{\mathrm{A}}=0.1r_{{\mathrm{Zn}}^{2+}}+0.9r_{{\mathrm{Fe}}^{2+}}\\ {\mathit{r}}_{\mathrm{B}}=0.1r_{{\mathrm{Zn}}^{2+}}+0.8r_{{\mathrm{Co}}^{2+}}+1.1r_{{\mathrm{Fe}}^{2+}}\end{array}$$ 4

The electrical and magnetic characteristics of ferrite materials are strongly influenced by their average crystallite size and particle distribution. The traditional Scherrer equation focuses on the most conspicuous (311) peak to determine the crystallite size using eq :

$${\mathit{d}}_{311}=\frac{0.94\lambda }{\beta \cos \theta }$$ 5

where θ is the diffraction angle, λ is the wavelength, and β is the peak’s full width at half-maximum. The obtained crystallite size value is listed in Table . This result confirms that the sol–gel synthesis method produces smaller crystallites. Combining precursors at the molecular level allows the production of homogeneous particles and controls the development of nanoparticles. The main reasons for the differences between nanocrystalline materials and their bulk counterparts are their higher surface area-to-volume ratio and the prevalence of grain boundaries. The physical and chemical properties of materials are strongly influenced by these elements. Zinc inclusions in cobalt ferrite matrices change the crystallite size by affecting the lattice strain and unit cell dimensions. Lattice expansion results from the greater ionic radius of Zn ions compared to that of Co ions. This development maintains the structure at nanoscale dimensions while allowing consistent grain development.

Physical factors affect the structural and magnetic properties, particularly the density and porosity. The X-ray density (ρ_X), bulk density (ρ_B), and porosity (P) were calculated using standard formulas. The obtained values are listed in Table . A higher ρ_X value indicates a strong spinel ferrite structure and shows the integration of larger Zn²⁺ ions (0.74 Å) into the crystal lattice, thereby increasing the unit cell volume. Ferrites with high porosity provide more active sites for chemical reactions and help increase interactions with biological surroundings, thereby supporting hyperthermia treatments and drug delivery systems.

Standard formulas were used to determine the hopping lengths L _A and L _B for Zn_0.2Co_0.8Fe₂O₄, and the obtained values are listed in Table . These measurements provide useful details regarding the structural organization and cation distribution within the spinel lattice. The tetrahedral (A-site) and octahedral (B-site) sublattices exhibit typical distances between adjacent cations. The observed low L _A value relative to L _B fits the usual properties of spinel structures, in which space restrictions cause tetrahedral locations to have shorter cation-oxygen bond lengths. However, in the octahedral sublattice, where the cations have more space, a larger L _B value indicates better cation-oxygen distances. The hopping lengths were altered by the addition of Zn²⁺ ions to the ferrite matrix. With a higher ionic radius (0.74 Å) than Co²⁺ (0.65 Å), zinc ions prefer to occupy both tetrahedral and octahedral sites, generating lattice expansion and contributing to the observed L _A and L _B values. These computed hopping lengths help define the magnetic and electrical characteristics of the material and reflect the spatial arrangement of the ions.

The oxygen positional parameters (U ^3m and U ^43m) were measured using standard spinel relations, and the obtained values are listed in Table . These measurements are essential for comprehending crystal distortions and bonding conditions, as they reveal the extent to which oxygen ions deviate from their ideal positions in a perfect cubic spinel structure. The magnetic and electrical properties of a material are significantly influenced by key lattice characteristics, such as cation-oxygen bond lengths and angles, which are heavily dependent on the oxygen spatial parameters. The near-perfect values observed suggest minimal distortion at both the A and B sites, thus preserving symmetry and stability. The introduction of Zn alters the local bonding environment of the alloy. Zinc ions preferentially occupy tetrahedral positions, as indicated by the spatial characteristics of oxygen, resulting in lattice expansion and the modification of bond lengths and angles. The slightly higher U ^43m value indicates that the octahedral sites experienced greater structural strain than the tetrahedral sites.

Using established equations, the bond lengths (d _AL and d _BL), lengths of shared edges (d _AE and d _BE), and lengths of unshared edges (d _BEU) were calculated. The results of the various calculations are listed in Table . These bond measurements play a crucial role in determining the magnetic and electrical characteristics of the materials. The Fe³⁺–O-Fe³⁺ superexchange interaction, which is fundamental to the magnetic properties of ferrites, is significantly influenced by the bond lengths and angles at both the A and B sites. The electrical conductivity and dielectric properties of the material are altered by changes in the bond lengths, which directly affect the electron hopping process between Fe³⁺ and Fe²⁺ ions.

Using the formulas from previous research. the bond angles, cation–cation (M–M) lengths, and cation–anion (M–O) distances were calculated and are listed in Table . These computations, based on extensive crystallographic studies, offer crucial new insights into bond measurements, angular relationships, and spatial arrangements of cations and oxygen anions within the spinel ferrite crystal structure. The symbols p, q, r, and s denote the mean bond lengths between the cations and oxygen in the tetrahedral (A-site) and octahedral (B-site) configurations, respectively. A minor increase in r and s compared to p and q indicates strain resulting from the substitution of smaller Co²⁺ ions (0.65 Å) with larger Zn²⁺ ions (0.74 Å), particularly in octahedral coordination. The parameters b, c, d, e, and f represent various interionic distances, including shared and unshared octahedral edges, tetrahedral–octahedral site interactions, and interstitial spaces. The increase in e and f values illustrates the effect of Zn doping on lattice expansion, which subsequently influences the density, porosity, and thermal stability of the material. These structural changes enhance the surface area, which is essential for applications such as catalysis and adsorption, while also improving biocompatibility for drug delivery and hyperthermia.

3.2. FTIR Analysis

FTIR spectra provide valuable insights into the molecular structures and bonding characteristics, which are essential for understanding their electrical, magnetic, and biomedical applications. The FTIR spectrum of Zn_0.2Co_0.8Fe₂O₄ is shown in Figure a. The stretching vibrations of metal–oxygen (M–O), particularly the Fe–O bonds at the octahedral sites of the spinel structure, were responsible for the peak at 547.08 cm^–1. This peak is important because it indicates that iron is present in the ferrite structure and provides details regarding the coordination environment of the metal ions. The other bands (1317, 1626, and 3350 cm^–1) observed in Zn_0.2Co_0.8Fe₂O₄ are associated with other vibrational modes of the sample, which are also aligned with the existing literature. The location and strength of these peaks provide valuable information regarding the extent of inversion in the spinel structure, which is essential for understanding the magnetic characteristics of the material. The exact position of this peak may be affected by variables such as particle size, cation distribution, and the existence of defects within the crystal structure. The intensity and width of these peaks provide insights into the crystallinity and homogeneity of the sample.

4.

FTIR spectra for (a) Zn_0.2Co_0.8Fe₂O₄ and (b) surface-coated Zn_0.2Co_0.8Fe₂O₄.

The FTIR spectra of the surface-coated samples are shown in Figure b. The functional groups detected in the FTIR spectra strongly confirm that the surface coating was effectively applied to the sample. The peaks observed at 780, 940, and 1083 cm^–1 belong to the SiO₄ asymmetric stretching, Si–OH, and Si–O–Si asymmetric stretching vibrations, respectively, which confirms the addition of Si to the sample. The peaks at 1380, 3430, and 3673 belong to the N–H bending and stretching vibrations and the O–H stretching vibration, respectively. These are associated with other vibrational modes of the sample, which are also aligned with the existing literature. ,

3.3. UV–Vis Analysis

The optical characteristics and electrical structure of the spinel ferrite nanoparticles can be better understood using UV–vis spectroscopy. Transition metal oxides are characterized by large absorption bands in the visible and near-IR regions of the spectrum. The room-temperature UV–vis absorbance spectrum of Zn_0.2Co_0.8Fe₂O₄ is shown in Figure . The main cause of the several absorption bands observed was the d-d electronic transitions of the Co²⁺ and Fe³⁺ ions in various coordination environments (tetrahedral and octahedral sites). The primary absorption bands typically occur in the 400–800 nm range, with specific band locations influenced by variables such as particle size, shape, and synthesis process. A prominent absorption band in the ultraviolet range (often below 400 nm) is frequently ascribed to ligand-to-metal charge-transfer transitions, which entail electron transfer from the oxygen 2p orbitals to the metal 3d orbitals. The absorbance (A) was obtained directly from the UV–vis spectra and is related to the transmittance (T) by the relation A = −log₁₀(T). Tauc’s relation was used to determine the value of the bandgap energy (E _g) from the relation (αhν) ⁿ = (Ahν – E _g). where α is the absorption coefficient, hν is the photon energy, A is a constant, and n depends on the electronic nature of the transition. A Tauc plot of (αhν)² versus hν (Figure inset) was used to measure E _g. The calculated energy gap of Zn_0.2Co_0.8Fe₂O₄ was found to be 2.14 eV, and a similar trend in the energy band gap value with Zn substitution has been reported by several researchers. , The relatively narrow bandgap indicates that the Zn-doped cobalt ferrite exhibits interesting optoelectronic properties. In addition, the optical bandgap of Zn_0.2Co_0.8Fe₂O₄, determined through UV–vis analysis, is important for its medical use. It affects the movement of the electrons in the material and its ability to generate reactive oxygen species (ROS). ROS are key factors in killing bacteria and cancer cells. A medium band gap helps form electron–hole pairs in normal or light conditions, leading to ROS that can harm bacteria and cancer cells.

5.

UV–vis absorbance spectrum and (inset) Tauc plot of Zn_0.2Co_0.8Fe₂O₄ nanoparticles.

Urbach Energy

The Urbach energy is the degree of the exponential tail of the absorption edge of semiconductors and insulators, and accounts for the absorption coefficient near the bandgap. This represents the range of energy, as a rule, which is close to the E _g value, increasing the absorption coefficient α with photon energy E exponentially. Understanding the influence of structural disorder on optical properties is becoming increasingly important because of the enhanced requirements for advanced materials with unique properties. The Urbach energy (E _U) was evaluated to understand the degree of disorder within the material based on the Urbach rule, α­(hν) = α₀ exp­(hν/E _U). The Urbach energy was extracted from the reciprocal of the slope in the exponential region of the absorption edge by plotting ln­(α) versus hν. The Urbach energies of Zn_0.2Co_0.8Fe₂O₄ are shown in Figure . The Urbach energy of Zn_0.2Co_0.8Fe₂O₄ was affected by the intricate interactions between the Zn, Co, and Fe ions at the tetrahedral and octahedral positions inside the spinel structure. A lower Urbach energy indicates a more ordered composition with fewer flaws, whereas an increasing value indicates more chaos and a higher concentration of localized states. Several factors affect the Urbach energy of Zn_0.2Co_0.8Fe₂O₄, including the manufacturing methodology, nanoparticle dimensions, and heat treatment methods. A careful study of the optical absorption spectra close to the band edge can help determine this value. The low measured Urbach energy for Zn_0.2Co_0.8Fe₂O₄ suggests an extraordinary crystal quality and few defects or impurities in the spinel structure. This trivial band tailing (E _U) exhibits a sharp absorption edge, lower subgap absorption, and better optical transmittance. The obtained E _U value (0.04 eV) is lower than the reported values for various spinel ferrites. , The low Urbach energy of the Zn_0.2Co_0.8Fe₂O₄ nanoparticles suggests their great potential for biomedical applications because of their higher crystallinity and minimal flaws, which ensure better biocompatibility and lower toxicity.

6.

Urbach energy of Zn_0.2Co_0.8Fe₂O₄ nanoparticles.

3.4. Thermogravimetric Analysis

3.4.1. Differential Scanning Calorimetry (DSC)

The DSC heat flow versus temperature plot for Zn_0.2Co_0.8Fe₂O₄ is shown in Figure . The three distinct thermal effects observed in the DSC curve elucidate the structural evolution of the Zn_0.2Co_0.8Fe₂O₄ nanoparticles. The thermal breakdown of the remaining organic compounds and/or desorption of water from the nanoparticle surface was indicated by an endothermic peak at 81.09 °C, with an ΔH value of −195.95 J/g. The dissociation of cobalt ferrite precursors or phase transition from cubic to monoclinic structure was evidenced by a secondary endothermic peak at 188.86 °C (ΔH = −19.89 J/g). An exothermic reaction at 272.45 °C with ΔH = 55.88 J/g indicates the oxidation of residual organic pieces or the crystallization or grain development of the sample. The calorimetric data suggest that the sample experienced considerable structural changes between 80 and 280 °C, which may account for the substantial variation in the magnetic properties.

7.

DSC heat flow vs temperature plot of Zn_0.2Co_0.8Fe₂O₄.

3.4.2. Differential Thermal Analysis (DTA)/Thermogravimetric Analysis (TGA)

The TGA and DTA instruments facilitated the measurement of the weight change of Zn_0.2Co_0.8Fe₂O₄ from ambient temperature to 900 °C at a heating rate of 10 °C/min. Figure shows the TGA and heat flow (DTA) against temperature curves. The TGA curve indicates the first (4.2%), second (8.27%), and third (2%) weight losses, totaling 14.47%, for temperature ranges of 25–149 °C, 165–277 °C, and 287–900 °C of material, respectively. The weight losses were ascribed to the evaporation of water molecules and disintegration of polymeric entities. The third weight loss of 2% within the material temperature range of 287–900 °C resulted from the breakdown of organic salts and the elimination of organic components. Beyond 900 °C, the curve exhibited minimal weight loss. The shallow endotherms and exotherms observed in the DTA curve within the temperature range of 40–335 °C correspond to the degradation of the material through heat absorption from the surroundings. The exotherm in the temperature range of 327–611 °C is attributed to the wide exotherm of energy release that facilitates phase formation. It can be concluded that the material approaches thermal stability, as there is no weight loss beyond 600 °C, and an exothermic peak is observed.

8.

DTA/TGA image of Zn_0.2Co_0.8Fe₂O₄.

3.5. FESEM Analysis

Surface morphology studies are essential for understanding the magnetic, electrical, and biological properties of ferrite materials. The field-emission scanning electron microscopy (FESEM) image of Zn_0.2Co_0.8Fe₂O₄ in Figure a shows that the Zn_0.2Co_0.8Fe₂O₄ nanoparticles were approximately spherical in shape. The grains have a uniform shape, are well-organized, and grow in a controlled manner during heating. The sharp edges and flat surfaces indicate that the particles grew unevenly, which is common for well-formed spinel ferrites synthesized at an ideal temperature of 900 °C. The average particle size of the sample was estimated using histograms obtained from the ImageJ software analysis. The average particle size was approximately 200 nm, confirming that the sample was in the nanoscale range. A histogram of Zn_0.2Co_0.8Fe₂O₄ is shown in Figure b. The uniform size of the particles in the sample indicates the effectiveness of the sol–gel technique. During sol–gel synthesis, the swift conversion from gel to powder and combustion of PVA (the chelating agent) produces significant heat. This thermal energy causes the initial nanoparticles to clump together and form larger aggregates. Such clustering is common in ferrite systems, where magnetic interactions between particles promote agglomeration during drying and calcination. Incorporating Zn²⁺ ions into cobalt ferrite affects the particle size by altering the lattice strain and growth kinetics. An increase in particle size diminishes surface-related magnetic and thermal losses, making the material suitable for magnetic hyperthermia applications that require uniform heating efficiency. The augmented size also improved the mechanical strength of the zinc-doped cobalt ferrites when employed as coatings or composite material fillers. Compositional elemental analysis of Zn_0.2Co_0.8Fe₂O₄ obtained by energy-dispersive X-ray spectroscopy revealed the atomic and weight percentages of O₂, Fe, Co, and Zn, providing insights into the stoichiometric consistency and chemical stability of the material. The energy-dispersive X-ray analysis (EDAX) spectrum of Zn_0.2Co_0.8Fe₂O₄ is shown in Figure c. The elevated atomic and weight percentages of O₂ indicated the oxide characteristics of the Zn_0.2Co_0.8Fe₂O₄ material and validated the presence of a spinel structure. The substantial weight percentage of Fe correlates with its abundance in the ferrite matrix because Fe ions are distributed over both the A and B sites, maintaining the stoichiometry of the ferrite complex. Co comprised 13.02% of the atomic percentage and 20.97% of the mass percentage, signifying its function as the principal divalent cation at site B. The reduced atomic percentage of Zn (2.91%) relative to Co²⁺ corresponds to the replacement rate of Zn²⁺ ions in the cobalt ferrite lattice, which validates the anticipated Zn_0.2Co_0.8Fe₂O₄ composition. The surface was coated with APTES, as confirmed by the EDAX analysis (Figure d). The presence of Si in the sample was due to SiO₂ coated with NH₂ functionalization NPs.

9.

(a) FESEM image, (b) histogram, and (c) EDAX spectrum of Zn_0.2Co_0.8Fe₂O₄ and (d) EDAX spectrum of surface-coated Zn_0.2Co_0.8Fe₂O₄.

3.6. Direct-Current (DC) Electrical Conductivity

Understanding the electrical conductivity of ferrite samples is important for various applications, such as sensors, memory, electromagnetic devices, and biomedical applications. The temperature variation of the DC electrical conductivity of Zn_0.2Co_0.8Fe₂O₄ is shown in Figure . The conductivity of Zn_0.2Co_0.8Fe₂O₄ was 1.5137 × 10^–3 Ω/m. This is due to the mobility of the charge carriers, particularly the electron-hopping mechanism between the Fe²⁺ and Fe³⁺ ions located at the B-site in the spinel lattice. This electron-hopping mechanism is strongly influenced by cation redistribution and the grain size of the ferrite material. Figure shows that the activation energies ω₁ and ω₂ are 0.0056 and 0.1620 eV, respectively. Small polaron hopping at B sites influences the conduction mechanism in low-temperature regions. In high-temperature regions, the conduction mechanism shifted to long-range polaron hopping at high temperatures. Incorporating Zn²⁺ ions into Co ferrite increased the lattice distortion, modifying the arrangement of Fe³⁺ and Fe²⁺ ions across the A and B sites. Due to the nonmagnetic and larger ionic radius of Zn²⁺, the A site is preferred, which results in increased strain and alters the charge transport mechanism. This leads to an increase in the energy barrier at high temperatures.

10.

Plot of log­(σT) vs temperature of Zn_0.2Co_0.8Fe₂O₄.

3.7. Dielectric Properties

The measurement of dielectric properties is essential for various electromagnetic device applications. Spinel ferrites exhibit a high dielectric constant at low frequencies. The dielectric properties of ferrite materials depend entirely on the synthesis method, sintering temperature, particle size, and cation distribution. The dielectric constant, dielectric loss, tan δ, and AC conductivity of Zn_0.2Co_0.8Fe₂O₄ were calculated using standard formulas. The frequency variations of the dielectric constant and dielectric loss of Zn²⁺ added to cobalt ferrite are shown in Figure a,b, respectively. The dielectric constant and dielectric loss graphs do not display a distinct resonant peak; instead, both metrics exhibit a typical steady decrease as the frequency increases, which is indicative of the standard dielectric dispersion behavior in ferrite materials. Figure a,b shows that the dielectric constant and dielectric loss decrease with increasing frequency due to space charge polarization, which aligns with Maxwell–Wagner polarization. The observed polarization behavior in Zn_0.2Co_0.8Fe₂O₄ indicates that the dielectric constant is affected by the charge moments inside the material and the existence of grain boundaries. The larger ionic radius of Zn²⁺ expands the lattice and allows more polarization. The dielectric characteristics of ferrites, namely Zn_0.2Co_0.8Fe₂O₄, are closely associated with their electrical configuration and charge transport processes. The polarization process in these materials parallels their electrical conduction, resulting in the movement and reorientation of the charge carriers inside the crystal lattice. The dielectric response and AC conductivity of the spinel structure depend on the movement of electrons between Fe²⁺ and Fe³⁺ ions. The frequency-dependent features of the alternating current conductivity (σ_AC) and loss tangent (tan δ) are shown in Figure . The loss tangent of Zn_0.2Co_0.8Fe₂O₄ decreased as the frequency increased, indicating a better energy storage efficiency at higher frequencies. This effect is linked to reduced energy dissipation resulting from the poor capacity of dipoles to monitor rapidly fluctuating electric fields. In contrast, the AC conductivity of typical spinel ferrites shows a power-law increase with frequency. This effect is primarily related to the higher mobility of charge carriers between Fe²⁺ and Fe³⁺ ions at the octahedral sites under the impact of the alternating field. Incorporating Zn into the cobalt ferrite structure further altered these features by changing the cation distribution and Fe²⁺ concentration, thereby influencing the activation energy for the hopping conduction. These data correspond to the tiny polaron concept, in which localized electrons traverse via thermally induced hopping processes, offering significant insights into the charge transport mechanisms in this oxide material.

11.

(a) Dielectric constant and (b) dielectric loss of Zn_0.2Co_0.8Fe₂O₄.

12.

(a) AC conductivity and (b) tan δ of Zn_0.2Co_0.8Fe₂O₄.

3.8. Mössbauer Spectra

Mössbauer spectroscopy provides detailed information on the electrical and magnetic surroundings of Fe ions in spinel ferrite structures. The capability of this technique to identify alterations in the nuclear energy levels of Fe atoms facilitates the accurate characterization of their oxidation states, coordination geometries, and magnetic characteristics. In spinel ferrites, the spectra generally exhibit a complicated interaction between Fe³⁺ ions in tetrahedral (A-site) and octahedral (B-site) positions and the possible existence of Fe²⁺ ions or structural defects. The two sextets (A and B) in the Mössbauer spectra provide critical insights into the magnetic ordering and site occupancy of Fe³⁺ ions. Sextet A, tetrahedral configurations of Fe³⁺ ions, often exhibit a higher hyperfine field resulting from stronger covalent bonds. In contrast, sextet B usually shows a decreased hyperfine field related to Fe³⁺ ions organized in an octahedral shape. The relative intensities of these sextets yield critical insights into the cation distribution and degree of inversion within the spinel framework. The presence of a doublet in the spectra may suggest the presence of Fe²⁺ ions, potentially influencing the material characteristics, or may indicate structural defects that alter the environment of specific Fe ions.

The Mössbauer spectral examination of Zn_0.2Co_0.8Fe₂O₄, shown in Figure , reveals crucial information about its hyperfine interactions and the distribution of cations; the obtained values are listed in Table . The spectra exhibited two sextets (A and B) and one doublet, each representing a distinct iron environment in the spinel structure. The tetrahedral (A) sites of sextet A are associated with Fe³⁺ ions, as evidenced by the hyperfine magnetic field (H _hf) of 47.06 T. Conversely, Sextet B, with H _hf = 41.50 T, is associated with Fe³⁺ ions located at octahedral (B) sites. Chintala et al. reported that the observed distribution of Fe ions was consistent with previous findings on spinel ferrites. Isomer shift (δ) measurements for sextets A (0.316 mm/s) and B (0.350 mm/s) validated the Fe³⁺ oxidation state. The octahedral sites displayed a slightly higher δ, indicating a more covalent electronic environment, consistent with earlier research on cation distribution in doped ferrites. The isomer shift of the doublet (0.362 mm/s) and the significant quadrupole splitting (Δ = 0.825 mm/s) indicate the existence of Fe²⁺ ions, probably due to Zn²⁺ substitution and the resulting lattice distortions. These doublets indicate the mixed-valence states or structural aberrations observed in ferrites. The Fe³⁺ ions appear to be surrounded by symmetric local environments, as indicated by the smallest quadrupole splitting values for sextets A (−0.001 mm/s) and B (0.015 mm/s). However, the broader line width of sextet B (1.664 mm/s) indicates magnetic interactions and site inhomogeneity, phenomena that are frequently observed in substituted ferrites because of cation redistribution. The relative area (RA) of sextet B (55.1%) exceeds that of sextet A (38.7%), validating the dominant presence of Fe³⁺ ions at octahedral sites, which is a defining characteristic of Zn- and Co-doped spinel ferrites.

13.

Mossbauer spectra of Zn_0.2Co_0.8Fe₂O₄.

2. Values of Hyperfine Field (H _hf), Isomer Shift (δ), Quadrupole Splitting (Δ), Line Width (Γ), and Relative Area (RA) in the Percentage of Fe-Ion Sites for the ZP sample Derived from the Mössbauer Spectra Recorded at Room Temperature.

sample code	iron site	Hhf (T) ± 0.1	Δ (mm/s) ± 0.05	δ (mm/s) ± 0.03	Γ (mm/s) ± 0.05	RA (%)
ZP	sextet A	47.06	–0.001	0.316	0.874	38.7
	sextet B	41.50	0.015	0.350	1.664	55.1
	doublet	–	0.825	0.362	0.811	6.2

^aThe isomer shift values are relative to the Fe metal foil (δ = 0.0 mm/s).

3.9. VSM Analysis

The study of magnetic properties such as saturation magnetization (M _s), coercivity (H _c), remanence (M _r), and squareness ratio (M _r/M _s) are important for various applications such as magnetic sensors, data storage, targeted drug delivery, and magnetic hyperthermia. These properties depend on the preparation method, cation distribution, and particle size. The M–H loop of Zn_0.2Co_0.8Fe₂O₄ is shown in Figure . From the VSM data, the saturation magnetization (M _s = 37.16 emu/g), coercivity (H _c = 0.209 Oe), remanence (M _r = 4.71 emu/g), and squareness ratio (M _r/M _s = 0.127) were calculated. The M _s value was influenced by the addition of Zn²⁺ ions, which reduced the M _s value owing to their diamagnetic nature. The M _s value depends on the magnetic exchange interactions between the A and B sites. The addition of Zn²⁺ alters the magnetic interactions between the A- and B-site cations and reduces the net magnetic moment of the material. However, the incorporation of Zn²⁺ ions minimized the internal strain, leading to a relatively enhanced M _s value, similar to that observed in the literature. , The obtained coercivity values confirm that the sample exhibited a soft magnetic nature. The addition of Zn²⁺ ions to Co ferrite results in a reduction in the anisotropic energy barrier by weakening the magnetic exchange interactions, which leads to an improvement in the domain wall moment. The particle size obtained by FESEM indicates the single-domain nature of the particles. The lower M _r value also indicates the soft magnetic nature of Zn_0.2Co_0.8Fe₂O₄. The squareness ratio is the ratio of the remanence magnetization to the saturation magnetization (M _r/M _s). It plays an important role in evaluating material hardness. The squareness ratio obtained for Zn_0.2Co_0.8Fe₂O₄ was 0.127, which was below 0.5, indicating that the sample had a single-domain structure. The magnetic properties of the Zn_0.2Co_0.8Fe₂O₄ sample make it suitable for magnetic hyperthermia and biomedical applications.

14.

M–H loop of Zn_0.2Co_0.8Fe₂O₄.

3.10. Antibacterial and Antifungal Activity Tests

The disc diffusion method was used to evaluate the antibacterial and antifungal efficacy of Zn_0.2Co_0.8Fe₂O₄ nanoparticles against Escherichia coli and Aspergillus niger. Overnight cultures of these bacteria were cultivated to establish vigorous populations, which were then inoculated onto agar plates. For a homogeneous dispersion, a 2 mg/mL stock solution of nanoparticles was prepared in sterile water and sonicated. Samples from this solution were transferred onto inoculation plates and incubated for 24 h at 37 ± 0.1 °C. , Assessing the zones of inhibition, which are the areas where microbial growth is halted during the incubation period, is essential for evaluating the antibacterial efficacy of nanoparticles. The antibacterial and antifungal activities of Zn_0.2Co_0.8Fe₂O₄ are shown in Figure .

15.

(a) Antibacterial and (b) antifungal activities of Zn_0.2Co_0.8Fe₂O₄.

The findings of this study demonstrate the notable antibacterial activity of Zn-doped cobalt ferrite nanoparticles against various bacterial and fungal species. A 13 mm inhibitory zone was observed for E. coli, demonstrating significant antibacterial activity. Antifungal tests showed considerable activity against A. niger, as evidenced by an inhibition zone of approximately 12 mm. The results showed that the Zn_0.2Co_0.8Fe₂O₄ nanoparticles exhibited strong antibacterial properties, preventing the growth of fungi and bacteria. According to these studies, Zn-doped cobalt ferrite nanoparticles may be effective antibacterial agents, reducing the increasing problem of antibiotic and antifungal resistance in several ways. The improved antibacterial effectiveness of the material is due to the direct interaction of nanoparticles with the bacterial cell membrane, metal ion interactions, and ROS generation. ROS generation is a key factor in explaining the antimicrobial and cytotoxic effects of the ferrite nanoparticles. Transition metal ions such as Fe³⁺ and Co²⁺ in Zn_0.2Co_0.8Fe₂O₄ can catalyze Fenton-like reactions, thereby enhancing the production of ROS. The antimicrobial mechanism of Zn_0.2Co_0.8Fe₂O₄ nanoparticles is illustrated in Figure . ROS induce oxidative stress and damage micro-organizational components. Together with direct physical interactions between nanoparticles and microbial cell membranes, this method helps Zn_0.2Co_0.8Fe₂O₄ to be generally efficient against a wide variety of pathogens.

16.

Antimicrobial mechanism of Zn_0.2Co_0.8Fe₂O₄.

3.11. Cytotoxicity Analysis

Evaluating the cytotoxic effects of the synthesized Zn_0.2Co_0.8Fe₂O₄ and Zn_0.2Co_0.8Fe₂O₄@SiO₂-NH₂ nanoparticles is crucial for their application in biomedical research. Hyperthermia is a novel anticancer therapy. It generates more heat in the tumor cells, thereby making them sensitive. Because tumor cells are surrounded by healthy cells, it is crucial to determine the nanoparticle dosage to ensure that adjacent normal cells are not damaged. A graphical representation of the percentage of viable MCF-10A and MCF-7 cells is shown in Figure .

17.

Graphical representation of the percentages of viable MCF-10A and MCF-7 cells after treatment with Zn_0.2Co_0.8Fe₂O₄ and Zn_0.2Co_0.8Fe₂O₄@SiO₂-NH₂ nanoparticles.

An MTT assay was performed to evaluate the cytotoxic effects of these nanoparticles on breast cancer cell lines (MCF-7) and normal breast cell lines (MCF-10A). Briefly, increased concentrations (100, 200, 300, 400, 500, and 1000 μg/mL) of Zn_0.2Co_0.8Fe₂O₄ and Zn_0.2Co_0.8Fe₂O₄@SiO₂-NH₂ nanoparticles were exposed to the proliferating MCF-7 and MCF-10A cells. Neither nanoparticle exhibited cytotoxicity in the MCF-10A normal breast cell line, even at higher concentrations of nanoparticles. In MCF-7 cells, cell viability decreased with increasing concentration. The IC50 is defined as the inhibitory concentration at which half of the cells die. MCF-7 cells treated with 400 μg/mL Zn_0.2Co_0.8Fe₂O₄ nanoparticles showed 52% cell viability, whereas, at 100 μg/mL of Zn_0.2Co_0.8Fe₂O₄@SiO₂-NH₂, MCF7 cells showed 53.9% cell viability, suggesting that Zn_0.2Co_0.8Fe₂O₄@SiO₂-NH₂ is comparatively toxic to the breast malignant cell line MCF-7 at a lower concentration i.e. of 100 μg/mL when compared with Zn_0.2Co_0.8Fe₂O₄. The obtained values showed better biocompatibility than those in existing reports prepared using different synthesis methods. As shown in the graph, MCF-7 cell viability decreased with increasing concentrations of both nanoparticles, whereas Zn_0.2Co_0.8Fe₂O₄@SiO₂-NH₂ showed cytotoxicity at a lower concentration.

Assessing the cytotoxicity of the resultant nanoparticles is important for evaluating their safety and biomedical application potential, especially for cancer treatment. In the present study, we evaluated the cytotoxic effects of Zn_0.2Co_0.8Fe₂O₄ and SiO₂-NH₂-functionalized Zn_0.2Co_0.8Fe₂O₄ nanoparticles on human breast normal cell line (MCF-10A) and breast cancer cell line (MCF-7) to assess their therapeutic potential. The results revealed that both nanoparticle formulations exhibited selective cytotoxicity toward MCF-7 breast cancer cells while maintaining high biocompatibility with normal MCF-10A epithelial cell line. Notably, Zn_0.2Co_0.8Fe₂O₄@SiO₂-NH₂ nanoparticles demonstrated significantly enhanced cytotoxicity at lower concentrations, with a markedly reduced IC₅₀ value compared to the uncoated counterpart.

The improved therapeutic efficacy of the functionalized nanoparticles might be due to enhanced cellular uptake, increased surface reactivity via amine groups, and potential mechanisms such as membrane disruption and ROS generation. Furthermore, the silica shell contributes to improved dispersion stability and facilitates efficient intracellular delivery. Future in vivo studies and mechanistic evaluations are warranted to further validate their clinical utility.

4. Conclusions

The Nanocrystalline Zn_0.2Co_0.8Fe₂O₄ sample was synthesized using the sol–gel autocombustion method. XRD studies of the sample confirmed a single-phase cubic spinel structure. The experimental lattice parameter was determined to be 8.3899 Å. Various structural parameters, such as oxygen positional parameters, bond lengths, bond angles, and A- and B-site hopping lengths, were calculated, which supported the estimated cation distribution. The presence of a single phase in the sample was also confirmed by FTIR spectroscopy, and the surface coating of the sample was identified. FESEM image studies confirmed that all the particles were of uniform size and spherical in nature. The stoichiometry of Zn_0.2Co_0.8Fe₂O₄ was confirmed using EDAX analysis. The surface coating with APTES was also confirmed by the EDAX analysis. TGA analysis showed the thermal stability of the materials, and no weight loss was observed beyond 600 °C. The optical energy bandgap was determined using Tauc plot calculations. The low Urbach energy suggests that Zn_0.2Co_0.8Fe₂O₄ has great potential for application in biomedicine. Variable-temperature DC electrical studies indicated the semiconducting nature of the sample. The dielectric properties of the sample exhibited normal dielectric behavior with respect to the applied frequency. Mössbauer studies also supported the estimated cation distribution. Studies on the magnetic characteristics showed a soft magnetic nature. The obtained saturation magnetization of 37.16 emu/g confirms the sample’s ferromagnetic nature. These findings underscore the potential of Zn_0.2Co_0.8Fe₂O₄@SiO₂-NH₂ nanoparticles as promising candidates for targeted cancer therapy. Their ability to preferentially affect malignant cells while sparing healthy cells highlights their applicability in precision nanomedicine approaches, particularly in magnetic hyperthermia and drug delivery systems. The obtained antimicrobial and low cytotoxicity values suggest that the Zn_0.2Co_0.8Fe₂O₄ sample is suitable for biomedical and magnetic hyperthermia applications.

All data supporting the findings of this study are available within the article.

The authors declare no competing financial interest.