Insight into the synergistic antibacterial mechanism of bio ZnO nanoparticles synthesized from Sophora japonica flower buds extract

Developing green nanotechnology to produce safe and powerful nano-antimicrobials has become a hot direction for addressing the challenge of antibiotic resistance. In this study, to investigate the enhancement effect of bio-capping agents on the bioactivities of plant-mediated zinc oxide nanoparticles (ZnO NPs), we designed a facile one-step green method to obtain bio-functioned ZnO NPs using flavonoids-rich extract of S. japonica flower buds (ESJ). The characterization results revealed that crystalline ZnO NPs with sizes smaller than 15 nm were obtained and the resultant bio-NP consists of ZnO core capped by ESJ-derived biomolecules. The biomolecules promoted the ZnO NPs to adhere to the bacterial cells and penetrate into cells by trapping bacteria and altering membrane permeability, which enhanced the bioactivities of the green-synthesized bio ZnO NPs and reduced cytotoxicity. And the bio ZnO NPs showed minimum inhibitory concentrations (MIC) of 0.5 and 0.125 mg/mL toward Staphylococci aureus and Escherichia coli, respectively, and had good ⋅OH and DPPH radical scavenging activities with IC50 of 0.31 and 1.55 mg/mL, respectively. In addition, the bio ZnO NPs could maintain 80 % viability of NIH3T3 cells at 2*MIC (1 mg/mL). This study provides a thought for the design of highly effective antibacterial nanomaterials, which may kill bacteria by membrane-disruption action to evade drug-resistant antimicrobial mechanisms under the synergistic actions of plant-derived biomolecules.