Stabilized cationic dipeptide capped gold/silver nanohybrids: Towards enhanced antibacterial and antifungal efficacy

The nanoparticles of silver/gold and cationic peptides have been recognized as potent antimicrobials for long, but their combined effect has so far not been explored. The present study reports the green synthesis of short cationic dipeptide stabilized AuNPs/AgNPs based nanohybrid materials. It thoroughly investigates the effect of conjugation of short cationic peptides on the antimicrobial properties of metallic nanoparticles. In the context of the antimicrobial evaluation of synthesized nanoconjugates, it was observed that peptide capped AgNPs exhibited higher antimicrobial activity as compared to peptide capped AuNPs as well as native peptides and unconjugated metallic nanoparticles. Specifically, l-His-l-Arg-OMe capped AgNPs exhibited MIC of 0.50, 0.37 and 0.25μM against E.coli, S. aureus and S. typhimurium respectively and MIC of 0.80 and 10.00μM against C. albicans and C. glabrata respectively. These results indicate that synthetic dipeptides render AgNPs as better antimicrobial agents in comparison to the native AgNPs and positively charged dipeptides. In addition, the time kill profile of cationic peptide (l-His-l-Arg-OMe) capped AgNPs was found to be even better than the known antibiotics. The cytotoxic behavior of all synthesized nanoconjugates of cationic peptides was studied and was found to be within acceptable limits. The present study opens a completely new class of antimicrobials for combating a wide range of bacterial and fungal pathogens. Another interesting and crucial finding was that dipeptide capped AgNPs displayed maximum antimicrobial activity with observed approximate 2-10 fold reduction in nano formulation dosage against tested microbes.