Phyto-Assisted Synthesis and Investigation of Zinc Oxide Nanoparticles for Their Anti-Aging, Sun Protection and Antibacterial Activity

Objective: This study aimed to develop eco-friendly zinc oxide nanoparticles (ZnO NPs) using Punica granatum (pomegranate) peel extract and to evaluate their antioxidant, antimicrobial, and photoprotective potential. Method: ZnO NPs were synthesized via a green chemistry route employing polyphenol- and flavonoid-rich peel extract as reducing and stabilizing agents. The nanoparticles were characterized using FTIR, SEM, XRD, DSC, DLS, and UV–Vis spectroscopy. Biological activities were assessed through in vitro assays including antioxidant (DPPH), anti-collagenase, anti-elastase, anti-tyrosinase, antimicrobial activity, and SPF determination. In vivo photoprotective efficacy was further evaluated in UVB-irradiated rat models, with histological analysis to confirm structural skin changes. Results: The optimized ZnO NPs exhibited an average particle size of ~194 nm with a zeta potential of −18.2 mV, indicating good stability. They demonstrated notable antioxidant activity (DPPH IC50 = 52.91 µg/mL), substantial tyrosinase inhibition (72% at 200 µg/mL), and antibacterial activity with inhibition zones up to 19 mm against S. aureus and 17 mm against E. coli. The nanoparticles also showed excellent UV absorption, with an SPF value of 29.8, exceeding the FDA threshold for effective sun protection. In vivo, topical application of ZnO NPs in UVB-exposed rats led to a 69% reduction in epidermal thickness and preservation of collagen fibers compared with UV controls. Conclusions: These findings confirm that P. granatum peel extract–mediated ZnO NPs possess significant antioxidant, antimicrobial, and photoprotective activities.