Valorisation of Curcuma longa-Derived Silver-Zinc Oxide Nanocomposites with Antibiofilm and Photocatalytic Activity Against Multi-Drug-Resistant Pathogens and Cationic Dyes

Abstract

Purpose: Escalating contamination of water bodies with toxic synthetic dyes and antibiotic-resistant bacteria underscores an urgent need for effective, eco-friendly remediation strategies. This study investigated antioxidant, anti-biofilm, and photocatalytic potential of silver-zinc oxide nanocomposites (Ag/ZnO NCs) synthesized from methanolic extract of Curcuma longa. Methods and Results: UV-Vis spectroscopy, X-ray diffraction, and electron microscopy of Ag/ZnO NCs confirmed the synthesis. The Ag/ZnO NCs exhibited antibacterial activity against multidrug-resistant (MDR) pathogens, with minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) of 31.25 and 62.50 µg/mL, respectively. These pathogens included enteroaggregative E. coli (EAEC), Salmonella Typhimurium, S. Enteritidis, and methicillin-resistant Staphylococcus aureus (MRSA). DPPH- and ABTS-based antioxidant assays revealed dose-dependent increase in free radical scavenging activity. Biofilm formation on polystyrene plates was significantly (P < 0.001) inhibited across all the MDR test strains, with higher inhibition observed at 48 h, and against MRSA. Photocatalytic activity was assessed by exposing the bacteria to Ag/ZnO NCs under LED light (460 nm). At MIC (1X and 1/2X), MDR-EAEC was eliminated within 30–120 min, and Salmonella spp. and MRSA were undetectable at 120 min. Sub-MIC concentrations (1/5X and 1/10X) increased clearance time to 180–240 min. The Ag/ZnO NCs demonstrated significant dye degradation efficiency (23–85%; initial concentration of 5 ppm for methylene blue [MB] and rhodamine-B [RhB], and 50 ppm for crystal violet [CV]) for CV and MB under sunlight, LED and UV light, with a peak degradation of 92-98.4% at 105 min. RhB degradation was slower (38.90 and 88.96% in UV and LED), with enhanced degradation (98.37%) under sunlight. No significant differences could be observed in the selectivity of MB and CV; however, exhibited a significant difference for RhB (P < 0.01). Reused NCs exhibited marginally reduced dye degradation potential than fresh Ag/ZnO NCs. Conclusion: These findings contribute to the valorisation of plant-derived biomass for the green synthesis of functional NCs, aligning with sustainable waste-to-resource strategies. The green-synthesized Ag/ZnO NCs demonstrated strong antimicrobial, antioxidant, antibiofilm, and photocatalytic properties, highlighting their potential for sustainable applications in environmental remediation and infection control.