Green synthesis of flower-like ZnO nanoparticles mediated by paulownia tomentosa: characterization and drug delivery performance

This study reports an eco-friendly synthesis of hierarchically structured zinc oxide nanoparticles using Paulownia tomentosa leaf extract as a bio-template. The synthesized nanoparticles displayed a distinctive flower-like morphology developed through a threestage assembly process, confirmed by time-dependent morphological analysis. BET analysis revealed a mesoporous structure with type IV isotherms and H3 hysteresis loops. Spectroscopic characterization confirmed the wurtzite crystal structure with characteristic Raman modes at 438 cm⁻¹ (E2-high), 380 cm⁻¹ (A1-TO), and 583 cm⁻¹ (E1-LO). Surface modification with PEG-4000 enhanced the nanoparticles' performance as drug carriers, demonstrating Korsmeyer-Peppas model release kinetics (R² = 0.992) with a release exponent of 0.68. The nanostructures showed 2.3-fold higher drug loading capacity compared to conventional spherical ZnO particles. Biological evaluation revealed significant antimicrobial efficacy with inhibition zones of 28 mm against S. aureus and 24 mm against E. coli at 100 µg/mL concentration, while demonstrating selective cytotoxicity against MCF-7 breast cancer cells with minimal effect on normal breast epithelial cells.