SYNTHESIS AND CHARACTERIZATION OF IRON DOPED ZnO NANOPARTICLES VIA SOL-GEL PROCESS FOR POTENTIAL BIOIMAGING APPLICATIONS

Abstract

Pure Zinc Oxide nanoparticles (ZnO NPs) have gained considerable attention for nanomedical applications due to their biocompatibility, strong UV emission, and wide band gap. However, their intrinsic limitations, including unpredictable cytotoxicity, low stability in biological environments, and lack of intrinsic imaging capability, restrict their direct application in the field of bioimaging. This work focused on optimizing the synthesis parameters of Iron (Fe) doped ZnO NPs by varying the Fe doping concentration, growth temperature, and Glutathione (GSH) capping concentration to investigate the effects on optical, structural, and photoluminescence properties for their possible use in bioimaging. Iron-doped ZnO NPs were synthesized via the sol-gel technique with Fe doping (0.15 - 0.55% Fe), growth temperature from room temperature (RT) to 95 °C, and GSH capping (0.002 – 0.014 M). X-ray diffraction (XRD) confirmed the retention of a single-phase hexagonal wurtzite structure for all synthesized samples with no secondary phases. At a doping level of 0.45% Fe, the crystallite size was minimized to 22 nm, peak intensity increased, and microstrain decreased, indicating optimum crystallinity. Variation in growth temperature showed sharper peaks and minimal lattice strain at 65 °C. Capping with GSH reduced peak broadening, reflecting enhanced surface passivation. Photoluminescence (PL) spectroscopy displayed near band edge (NBE) UV emission (410-470 nm) across all samples. The intensity of PL was optimized at 0.45% Fe, 65 °C, and 0.008M GSH due to reduced non-radiative recombination. Optical analysis through UV Vis spectroscopy and Tauc analysis revealed a tunable band gap of 3.67 eV for Pure ZnO, narrowed to 3.02 eV at 0.45% Fe and 65 °C, and to 3.0 eV at 0.008M GSH capping, hence improving visible light emission. Fourier transform infrared spectroscopy (FTIR) confirmed the successful incorporation of Fe into Zn-O and FeO bonds without any secondary phases. FTIR displayed strong Zn–O stretching (830-915 cm⁻¹) across all concentrations with slight shifts, confirming lattice distortion from Fe³⁺ substitution. No iron oxide peaks appeared, indicating Fe was incorporated without secondary phases. GSH anchoring of the GSH was confirmed by N-H, C=O, and COO- vibrations, which are indicators of strong bonding to the surface of the ZnO and have offered a better stability to the nanoparticles. The overall findings identified the optimum synthesis conditions to be 0.45 % Fe, 65 °C, and 0.008 M GSH capping. The resultant Fe: ZnO NPs are of high crystallinity, low defect density, band gap tunability, and enhanced PL, making them promising candidates for stable, efficient luminescence bioimaging.