Antibiofilm activity of green-synthesised ZnO quantum dots by Tinospora cordifolia against modeled biofilm forming organisms

Biofilms are a group of syntrophic microbial associations that adhere to biotic and abiotic surfaces with the help of self-secreted extracellular polymeric substances (EPS). The EPS not only provides nourishment to the sessile micro-colonies but also prevents the penetration of drugs, resulting in the development of multi-drug resistance. Thus, to combat such a condition, the use of Zinc Oxide Quantum Dots (ZnO QDs) derived from the leaf extract of Tinospora cordifolia as an alternative therapeutic. Biofilm inhibition assay of ZnO QDs using crystal violet assay had demonstrated effective inhibition against biofilm formation, at concentrations between 50 µg/ml and 75 µg/ml. Further antioxidant potential of ZnO QDs was evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radical scavenging assays, showing an IC 50 of 0.65 mg/ml, surpassing that of the plant extract alone. Importantly, these ZnO QDs significantly reduced extracellular polymeric substances (EPS) components, including carbohydrates, proteins, and eDNA, which is crucial for biofilm stability. Additionally, the non-phytotoxicity ability of ZnO QDs has been displayed by plant seed germination tests, indicating its environmental friendliness. The study also revealed that ZnO QDs could penetrate biofilms, leading to substantial reductions in genomic DNA and RNA content in several bacterial strains. Chemotaxis assays with Poecilia sphenops indicated changes in behaviour and cellular integrity in response to varying ZnO QD concentrations. Lastly, ZnO QDs exhibited quorum-sensing inhibition by reducing auto-inducer levels and elastase activity, suggesting their potential antimicrobial activity as compared with conventional antibiotics. Together, these findings not only reflect the multifaceted antimicrobial performance of ZnO QDs but also the environmental compatibility and biosafety of these materials, making them highly applicable to future biomedical and ecological purposes • Green Synthesis of ZnO QDs . Zinc oxide quantum dots were successfully synthesized using Tinospora cordifolia leaf extract, confirmed via UV-Vis spectroscopy (peak at 325 nm), FTIR, SEM, and XRD analyses. • Potent Antibiofilm Activity . ZnO QDs effectively inhibited biofilm formation in multiple nosocomial pathogens (e.g., S. aureus , E. coli , P. aeruginosa ) through disruption of EPS components (carbohydrates, proteins, eDNA) and eradicated up to 96% EPS content. • Antioxidant Properties . ZnO QDs displayed strong free radical scavenging activity (DPPH IC₅₀: 0.32 mg/ml), significantly better than T. cordifolia extract alone. • Quorum Sensing Inhibition . ZnO QDs reduced auto-inducer, elastase, and AHL levels, and inhibited rhamnolipid-mediated swarming motility—showing antimicrobial action beyond growth suppression. • Non-Phytotoxic and Ecocompatible . ZnO QDs did not affect seed germination or plant DNA integrity at applicable concentrations and exhibited minimal impact on fish (Poecilia sphenops), indicating high environmental safety.