In-situ synthesis of gold nanoparticles as an indicator of unfolding and solid–liquid interfacial adsorption of proteins

Unfolding of highly hydrophobic water-insoluble proteins in aqueous phase is important to understand for their appropriate applications in food industry. Unfolding of wheat, rice, and zein proteins were determined by following the in-situ synthesis of Au nanoparticles (NPs) as indicators in aqueous micellar solutions of different anionic and cationic surfactants. The unfolding behavior was simultaneously monitored by UV–visible studies due to the surface plasmon resonance of Au NPs in the visible region while DLS size and zeta potential helped us in understanding the solid–liquid interfacial adsorption of protein–surfactant complex on Au NPs surface. Microscopic analysis and the Bradford method were used for characterizing and estimating the amount of protein conjugated to the Au NPs’ surface. Protein conjugated Au NPs were further used for estimating the isoelectric point (Ip) of solid–liquid interfacial conjugated protein which was quite different from the conventional solution-phase Ip of each protein. The results concluded that the unfolding temperature of zein was relatively lower than that of wheat and rice proteins because of its favorable solubilization in the micellar phase. It resulted in its preferential solid–liquid interfacial adsorption. Thus, unfolding and solid–liquid interfacial adsorption of proteins on nano metallic surfaces are interlinked phenomena of bionanomaterials with diverse applications in biological systems.