Biogenic Synthesis of ZnO Nanoparticles From <i>Heliotropium europaeum</i> and Assessment of Antibiofilm, Anti‐Quorum‐Sensing, Antioxidant and Anticholinesterase Activities

Abstract

ABSTRACT Zinc oxide nanoparticles (ZnO‐NPs) are inexpensive, non‐toxic, and biocompatible with human cells, making them suitable for biomedical applications. In the present study, ZnO‐NPs were synthesized from Heliotropium europaeum extracts at different concentrations through a green synthesis approach and characterized by UV, FTIR, XRD, and SEM‐EDX analyses. Different shapes and sizes of ZnO‐NPs were obtained: nanoparticles from plant powder (ZnNPs‐HEP, 27.02 nm), nanoparticles from plant extract at 7.5 g/L (ZnO‐NPs‐HE3, 24.5 nm), and 10 g/L (ZnO‐NPs‐HE4, 25.06 nm). These were tested for antimicrobial, antibiofilm, anti‐quorum‐sensing (QS), antioxidant and anticholinesterase activities. The smallest nanoparticles were ZnO‐NPs‐HE3, which exhibited the strongest antimicrobial activity, with minimal inhibitory concentrations (MICs) of 78.125 µg/mL ( S. aureus ), 312.5 µg/mL ( B. subtilis ), 156.25 µg/mL ( E. coli and C. albicans ), and 625 µg/mL ( S. typhi ). All ZnO‐NPs exhibited concentration‐dependent antibiofilm activity against S. aureus, B. subtilis, E. coli , S. typhi and C. albicans . Biofilm inhibition by ZnO‐NPs‐HE3 and ZnO‐NPs‐HE4 was comparable, suggesting that smaller size favors antibiofilm effects. ZnO‐NPs‐HEP exhibited the highest violacein inhibition against Chromobacterium violaceum CV12472, showing 100% inhibition at MIC, which decreased to 21.23% ± 1.84% at MIC/8. The QS inhibition zone against C. violaceum CV026 was 17.0 ± 1.1 mm (MIC) and decreased to 7.1 ± 0.3 mm (MIC/8). The ZnO‐NPs also showed strong inhibition of swimming and swarming motilities in Pseudomonas aeruginosa PA01, with ZnO‐NPs‐HE3 being most active. Antioxidant activities (DPPH • , ABTS •+ , and CUPRAC) and anticholinesterase activities (acetylcholinesterase and butyrylcholinesterase) ranged from low to moderate. Overall, the results demonstrate intrinsic antivirulence properties of ZnO‐NPs against pathogenic bacteria.