Thermal Stability, and Curvature Dependence of Bovine Serum Albumin on Gold Nanoparticles Using Localized Surface Plasmon Resonance

Gold nanoparticles exhibit Surface Plasmon Resonance (SPR), whose absorption peak is strongly dependent on the index of refraction, and coating thickness of the near surface region. A macromolecule bound to the nanoparticle will typically undergo a shift in index of refraction as its conformation changes, leading to a shift in the peak wavelength. Nanospheres can be made with a large variety of diameters, and present a novel method of looking at curvature dependencies of stability. In this study, Bovine Serum Albumin (BSA) was conjugated to Au nanospheres. Using a visible absorption spectrometer, the peak wavelength vs. temperature for eight diameters from 5nm to 60nm, was collected. Diameters above 20nm exhibited a continual increase in peak wavelength with temperature. Theoretical calculations indicate that this is a thickening of the protein layer. Below 20nm, peak wavelength shifts indicated a thinning of the BSA layer, and possible a decrease in index of refraction, followed by thickening at higher temperatures. Additionally, the study indicates that the peak shifts are highly time dependent, and a kinetic study has been performed at several temperatures.