Comprehensive Characterization and Biological and Safety Evaluation of Zinc Oxide-Curcumin Nanoconjugates: Unraveling...

Nanoparticles have been widely synthesized and used in various biological applications. Among the minerals, zinc (Zn) alters numerous biological pathways, and curcumin (Cur) functions mainly as the antimicrobial, anti-inflammatory, and anticancerous agent. In this study, nano-zinc oxide (nZnO), nano-curcumin (nCur), and its conjugate (nZnOcur) were synthesized through the chemical reduction method. The particles were characterized using UV-visible (UV-visible) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), high-resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS), and ζ-potential measurements. The UV-visible spectrum revealed that nZnO had an absorbance peak at 370 nm, while nCur had peaks at 400-600 nm, and the nZnOcur conjugate had peaks at 550-650 nm and a smaller peak in the 300-400 nm range. The key functional groups identified by FTIR confirm the successful conjugation of nZnOcur nanoparticles. XRD patterns indicated the crystalline wurtzite phase of nZnO with variations in peak intensity, suggesting structural changes upon curcumin incorporation. SEM-EDS and DLS analyses provided average particle sizes of 88.41 and 122 nm; 53.81 and 98 nm; 43.41 and 102 nm for nZnO, nCur, and nZnOcur conjugate, respectively. HR-TEM images showed that nZnO (∼70 nm, spherical) transformed into rod-like nZnOcur (∼105 nm) upon conjugation with curcumin. nZnOcur had higher antibacterial activity against bacterial strains, demonstrating synergistic effects. The antioxidant capacity was greater in both nCur and nZnOcur conjugates, while anti-inflammatory assays indicated significant protein denaturation inhibition with all three nanoparticles. Cytotoxicity tests revealed that nZnO had higher toxicity, and the acute oral toxicity study indicated nZnOcur conjugate as least toxic, with LD₅₀ value of 425.4 mg/kg. Overall, the findings underscore the nZnOcur conjugate as a promising and safer nanoparticle for antimicrobial, anti-inflammatory, and antioxidant applications with least side effects.