Altitude‐Adapted Rhododendron Arboreum‐Based Green Synthesis of Cu‐Doped and Undoped ZnO Nanoparticles with Enhanced Antibacterial Activity

The rise of antibiotic‐resistant pathogens necessitates eco‐friendly antimicrobial alternatives. This study reports the green synthesis of undoped and Cu‐doped zinc oxide nanoparticles (ZnO NPs) using Rhododendron arboreum leaf extracts from two altitudes (Chopta and Barlowganj), leveraging altitude‐driven phytochemical variation to enhance bioactivity. Characterization via UV–vis spectroscopy, XRD, FTIR, SEM, and TEM confirmed spherical ZnO NPs with a hexagonal wurtzite structure. Cu doping resulted in smaller particles (35.6 versus 45.2 nm) and reduced zeta potential (−30.2 versus −35.7 mV), indicating improved interaction with bacterial membranes. The UV–vis redshift (360 versus 340 nm) suggested a reduced bandgap. Chopta extracts exhibited significantly higher phenolics (327.18 mg GAE/g), flavonoids (31.91 mg QE/g), and saponins (0.82 mg/g) (p < 0.05), correlating with enhanced antimicrobial activity. Cu‐doped ZnO NPs showed antibacterial effects against multidrug‐resistant strains, with inhibition zones of 20–23 mm, MICs of 4–128 µg/mL, and biofilm inhibition of 78%–88%, highest against Pseudomonas aeruginosa (87.6%) and Bacillus. cereus (85.5%). LC–MS/MS identified bioactive compounds such as rutin, quercetin, and gallic acid, which may contribute to the enhanced antibacterial effects. These findings suggest that altitude‐adapted R. arboreum improves the bioactivity of Cu‐doped ZnO NPs, supporting their potential use in wound healing, coatings, and biofilm‐resistant materials.