Differently synthesized gold nanoparticles respond differently to functionalization with L-amino acids

The potential utility of gold nanoparticles(AuNPs)synthesized via different methods for biomedical applications vary greatly due to inherent differences in their surface properties.In the present study,we investigated the functionalization of AuNPs synthesized by chemical reduction,plant extract,and bacteria-mediated methods with 22 L-amino acids.Nanoparticles produced by bacteria-mediated(B_AuNPs)and plant-mediated(P_AuNPs)methods showed good potential,as they were able to be functionalized with six(histidine,lysine,methionine,phenylalanine,tryptophan,and tyrosine)and four(cystine,tryptophan,tyrosine,and valine)amino acids,respectively.In contrast,AuNPs produced by chemical reduction(C_AuNPs)were not found to be suitable for functionalization.Optimal functionalization conditions were found to be amino acid concentration of 20-25 mM and neutral pH(7)for P_AuNPs,whereas B_AuNPs tolerated more variable conditions.The electrophoretic mobility of P_AuNPs after functionalization indicated that these nanoparticles were less sensitive than B_AuNPs to the deviations from optimal conditions.A significant change in mobility was observed when B_AuNPs were functionalized with either methionine or tryptophan.Overall,the results of this study suggest that the suitability of the three differently synthesized AuNPs with amino acids is in the following order:B_AuNPs>P_AuNPs>C_AuNPs.