Green Synthesis of Zinc Oxide Nanoparticles Using Withania somnifera and Centella asiatica for Topical Herbal Skincare Applications

Background

Growing interest in herbal-based cosmetic products has encouraged the use of environmentally friendly nanotechnology for topical skincare applications. Zinc Oxide (ZnO) nanoparticles are widely used in skin formulations because of their antimicrobial, Ultraviolet (UV) protective, and anti-inflammatory properties; however, many conventional synthesis methods rely on hazardous chemicals.

Materials and Methods

In the present study, ZnO nanoparticles were prepared using a green synthesis approach with aqueous extracts of Withania somnifera (Ashwagandha) and Centella asiatica (Gotu Kola), two medicinal plants known for their antioxidant, antibacterial, and wound-healing properties. The nanoparticles were synthesized by reacting zinc acetate dihydrate with the plant extracts, followed by controlled alkaline precipitation using sodium hydroxide. Characterization using UV-visible spectroscopy, Fourier-Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), particle size analysis, and zeta potential measurements confirmed successful nanoparticle formation, surface stability, and phytochemical capping.

Results

High-Performance Liquid Chromatography (HPLC) analysis showed a maximum withanolide entrapment efficiency of 62.89%. In vitro release studies demonstrated a sustained release of bioactive compounds over an 8-hr period, supporting prolonged topical action. The prepared ZnO nanoparticles were incorporated into two topical cream formulations: a stearic acid-based emulsion and a beeswax-paraffin base. Both formulations showed desirable physicochemical characteristics, including skin-compatible pH (5.18-5.70), moderate viscosity (25,000-40,000 cps), good homogeneity, smooth texture, and stability under accelerated conditions. Antimicrobial testing against Staphylococcus aureus, Escherichia coli, and Candida albicans revealed greater inhibitory activity for ZnO nanoparticle-loaded creams compared to formulations containing only the herbal extracts.

Conclusion

Overall, the study demonstrates that combining green-synthesized ZnO nanoparticles with herbal bioactives offers a stable and promising approach for developing sustainable, nanotechnology-based skincare formulations.