Spectral interaction between silica coated silver nanoparticles and serum albumins

Herein, we report the interactions of serum albumins (SA) (human serum albumin (HSA) and bovine serum albumin (BSA)) with biocompatible silica coated silver nanoparticles synthesized via a simple environmentally benign synthesis, using N-[3-(trimethoxysilyl)propyl]-ethylene diamine (EDAS) as a reducing/stabilizing agent. The synthesized silica coated silver nanoparticles (Ag-EDAS) were well characterized using UV–visible spectroscopy, TEM, EDX, and STEM analysis. The steady state UV–visible absorption and fluorescence spectroscopic studies were performed to investigate the binding interaction between SA and silica coated silver nanoparticles. The apparent association constant was deduced (1.63 × 104 M−1 (HSA) and 3.23 × 104 M−1 (BSA)) from the absorption spectral changes of the SA in presence of silica coated silver nanoparticles using the Benesi–Hildebrand equation. Addition of silica coated silver nanoparticles, quenched the fluorescence of SA. The Stern–Volmer constant (KSV), quenching rate constant (kq), number of binding sites and the apparent binding constant were calculated from relevant fluorescence quenching data. Fluorescence decay analysis of serum albumins in the presence of silica coated silver nanoparticles shows decrease in lifetime which suggests the dynamic nature of the quenching process. Also protein conformational changes, in the presence of silica coated silver nanoparticles were studied using circular dichroism (CD) spectroscopy.