Effect of pH on Protein–Silver Nanoparticles Interactions at Nano-Bio Interface

Abstract

In promising areas of nanomedicine and nano-diagnostics, proteins are applied for bio-functionalization of nanoparticles to obtain biocompatibility for various applications ranging from bio-sensing, diagnostics to drug delivery etc. In all such applications, silver nanoparticles (AgNPs) are being utilized for their unique physicochemical and biological properties. These interact with proteins and other biomolecules affecting their structure and function. Therefore, it has become necessary to understand and control protein-nanoparticles interactions to gain an insight on such affects. Among proteins, Bovine Serum Albumin (BSA) has established itself as a model system for functionalization due to its broad range physiological properties. In the present study we investigated the interaction between silver nanoparticles and BSA at different pH conditions while ranging the protein (BSA) concentrations using spectroscopy techniques like UV-VIS and Fluorescence spectroscopy. Silver nanoparticles for this purpose were first synthesized by chemical co-reduction method using sodium borohydride and tri sodium citrate as reducing agents. Dynamic Light Scattering (DLS) results depicted the presence of AgNPs of size ranging between 13-62 nm with average particle size of 29 nm. UV-VIS spectra showed SPR band of AgNPs at 395 nm and after interaction with BSA ranging at different concentrations showed sensitivity towards any interactions with proteins (BSA). The interaction between BSA and AgNPs were also monitored at various pH ranging from 4 to 7 using UV-Vis spectroscopy. Results indicate that regardless of pH value, increasing BSA concentration up to 5 μM contributed towards a sharp decrease in characteristic SPR peak of AgNPs, which is attributed to the stable AgNP-BSA interactions. Further increase in BSA concentration (> 5μM) however caused a gradual red shift in SPR signals of AgNPs which indicates the extent of aggregation of silver nanoparticles in protein solution and hence limit their stability and efficacy under similar physiological conditions. The fluorescence spectra corroborates with UV-Vis data showing higher intensity at 350 nm of BSA which gradually increased hence, indicative of binding between AgNPs and BSA.