Superior Antimicrobial Activity of Ag-ZnO Bimetallic Nanoparticles Synthesised Using Hemigraphis colorata (Blume) Over ZnO Nanoparticles in Free and Collagen Coated form Against Wound Pathogens

Antibiotic resistant bacterial infection in the chronic wounds poses a significant threat to the human health. This necessitates the development of novel wound dressings with multi-mechanistic effects on the wound healing and pathogen control. To address this challenge and to promote more effective wound healing, this study has been deigned to investigate the therapeutic promises of green synthesized zinc oxide (ZnO) and silver-zinc oxide (Ag-ZnO) bimetallic nanoparticles (BMNPs) using the aqueous extract of Hemigraphis colorata. The synthesized BMNPs were found to have superior potential for combating the wound pathogens and also to accelerate the wound healing. The characterization of green synthesized ZnONPs and BMNPs was performed in the study by using UV-Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and high resolution transmission electron microscopy (HR-TEM). Here, the HR-TEM analysis has revealed the synthesized ZnONPs and BMNPs to have diameter of 7-20 nm range and 4-20 nm respectively. Antibacterial evaluation of BMNPs has further demonstrated its superior activity when compared with the ZnONPs against the selected wound pathogens, such as Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. This has further been evidenced by the lower minimum inhibitory concentrations (MICs) of BMNPs (0.312, 0.625, 0.625 and 0.312, mg/mL) respectively against S. aureus, E.coli, K. pneumoniae, and P. aeruginosa when compared with the same for ZnONPs alone (0.625, 1.25, 1.25, 0.625 mg/mL). Furthermore, field emission scanning electron microscopy (FE-SEM) analysis showed the morpho-mechanistic insights into the mode of action of BMNPs due to the disruption of intact cellular morphology of treated organisms. Here, the untreated E.coli and S.aureus were observed to have the normal rod-like and cocci-like cellular morphology which is confirmatory to the disruption observed in treated cells as to be due to the action of BMNPs. Up on further coating on collagen, the BMNPs were found to retain its antimicrobial activity against the tested pathogens as evidenced by the formation of zone of inhibition. This further indicates the BMNPs biofabricated in the current study to have the promises for clinical applications. In addition, cytotoxicity analysis by MTT assay has demonstrated the BMNPs to have minimal toxicity on L929 cell lines. Here, 96% of cell viability could be observed when the L929 cell line was treated with 6.25 mu g/mL concentration of BMNPs. These results suggest the promising potential of the synthesized BMNPs, particularly when incorporated into the collagen-based wound dressings, for promoting effective wound healing.