Evidence of charge donation through synergistic effect of bioconjugated silver nanoparticles with flavanols accomplishing augmented antimicrobial and antioxidant activities

Abstract

The current investigation reports the significant synergistic antibacterial and antioxidant potential of bioconjugated silver nanoparticles (AgNPs). Firstly, a simple chemical reduction process is employed to produce borate-stabilized AgNPs (C-Ag), and utilized to form a bioconjugate with antioxidants namely grape seed extract (GSE), (+) catechin (CT) and (-) epicatechin (ECT). In the second method, the bioconjugates are obtained by the bio-derived process. Bioconjugated AgNPs exhibit its plasmon resonance band at 427 nm which is relatively bathochromic shifted with respect to chemically synthesized pristine AgNPs. The bioconjugation of ECT with C-Ag exhibits a higher antioxidant activity against 1,1-diphenyl 2-picrylhydrazyl with half-maximal inhibitory concentration (IC50) of 21.32 µL/mL and an enhanced antibacterial activity against Staphylococcus aureus. Bioderived AgNPs-ECT bioconjugate shows the superior scavenging ability against 2,2-Azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (IC50 of 17.83 µL/mL) and shown potent synergistic effect against Escherichia coli bacteria. The spontaneous bioconjugate formation, intermolecular charge transfer, tendency of chemical reactivity and nature of interaction between CT/ECT with Ag have been investigated through density functional theory, which second the experimental results.