Biogenic zinc oxide nanoparticles from Saraca asoca: cytotoxicity, antioxidant, antimicrobial evaluation, and topical gel development

Background: Green synthesis of nanoparticles offers an eco-friendly and cost-effective alternative to conventional methods. Saraca asoca, a traditionally valued medicinal plant, contains bioactive compounds suitable for the fabrication of nanoparticles. This study reports the synthesis of zinc oxide nanoparticles (ZnO NPs) using Saraca asoca bark apozem and their incorporation into a biocompatible chitosan gel for topical applications. Methodology: ZnO NPs were synthesized via a green route using varying concentrations of zinc acetate (0.05–0.15 M) and Saraca asoca bark apozem (75–150 mg/mL), optimized through a 3² factorial design. The nanoparticles exhibited favorable formulation efficiency with % yield (40–46%), entrapment efficiency (55–62%), and drug loading (35–40%). Characterization confirmed nanoscale size (72.7–134.8 nm), negative zeta potential (–38.2 to –50.4 mV), UV–Vis absorbance (λmax = 366 nm), FTIR peaks of stabilizing –OH and –COO⁻ groups, and crystalline PXRD patterns. The optimized nanoparticles were incorporated into a 2% chitosan gel (Ash–ZnO NPs Cs gel). Results and Discussion: Antioxidant studies revealed strong free radical scavenging potential (IC₅₀ = 19.8 µg/mL). The Ash–ZnO NPs exhibited antimicrobial activity against Staphylococcus aureus and Candida albicans (MICs: 156.25 and 78.12 µg/mL). Cytotoxicity studies confirmed negligible toxicity (LC₅₀ > 1000 µg/mL). In vitro release studies demonstrated sustained and diffusion-controlled drug release, with Ash–ZnO NPs Cs gel achieving 96% release at 48 h compared to the burst release of silver nitrate gel. Conclusion: Saraca asoca-mediated ZnO NPs incorporated in chitosan gel represent a safe, stable, and multifunctional topical formulation. Their strong antioxidant, antimicrobial, biocompatible, and sustained release properties underscore their potential for wound healing and skin infection management.