Spectroscopic study on interaction of Nymphaea nouchali leaf extract mediated bactericidal gold nanoparticles with human serum albumin

Abstract

We have reported the eco-friendly gold nanoparticles (AuNPs) from 15% aqueous leaf extract of therapeutic plant Nymphaea nouchali where leaf extract acts as both reducing and stabilizing agents. The generation of AuNPs was confirmed by UV–visible spectroscopy, FTIR, FE-SEM, DLS, and the size and morphology were further confirmed via TEM analysis (average d = 54.7 nm). The existence of gold signal in EDX spectrum and measurement of zeta potential reveals a negative value (−21.7 mV) clearly indicates its stability. This synthesized AuNPs shows strong in vitro bactericidal effect against E. coli (DH5-Alpha) with 0.12 nM minimum inhibitory concentration, suggests its progress in therapeutic efficacy. The interaction of this AuNPs with human serum albumin (HSA) was investigated by UV–visible, FTIR, fluorescence, circular dichroism spectroscopies and zeta potential evaluation at 25 °C. It has been observed that the interaction mechanism is a static quenching process with the slightest change in the HSA secondary conformation because of HSA-AuNPs conjugate formation, but the primary structure remains unaffected. Negative free energy change indicates, the HSA-AuNPs formation is a thermodynamically favourable process. This analysis may offer a valuable information on the healthier antibacterial AuNPs synthesized from a medicinal plant extract.