Sustainable Fabrication of Zinc Oxide Nanoparticles Using Assam Green Tea Extract with Promising Oral Antimicrobial Potential

In this study, zinc oxide nanoparticles (ZnO NPs) were synthesized via a green chemistry approach using aqueous extract of Camellia sinensis var. assamica (Assam green tea) as a bioreductant and stabilizing agent. Phytochemical analysis of the extract revealed high levels of phenolics (338.57 ± 3.90 mg GAE/mL) and flavonoids (123.92 ± 1.34 µg QE/mL), along with strong antioxidant and reducing activity, supporting its efficacy in nanoparticle formation. ZnO NPs were synthesized at various extract concentrations, with 25% yielding optimal characteristics based on UV–Vis spectrophotometry (λMax ≈ 390–410 nm). Structural characterization using XRD confirmed the hexagonal wurtzite phase, and SAXS indicated particle sizes of 58–60 nm. FE-SEM analysis showed semi-spherical agglomerated particles ranging from 74 to 76 nm, while EDX verified the elemental purity of Zn and O. FT-IR spectroscopy confirmed the presence of Zn–O stretching and phytochemical residues on the nanoparticle surface. Stability studies over four weeks revealed red shifts in absorbance and reduced peak intensity at ambient and elevated temperatures, suggesting nanoparticle agglomeration. Antimicrobial assays demonstrated strong antifungal activity of the ZnO NP solution against Candida albicans and, upon concentration, significant antibacterial activity against Streptococcus mutans. The synthesized ZnO NPs exhibit promising potential as eco-friendly antimicrobial agents, particularly for applications in oral healthcare.