A fluorescence technique for investigating protein adsorption phenomena at a colloidal silica surface

Abstract

A fluorescence method for monitoring protein adsorption phenomena has been developed utilizing an unmodified spectrofluorometer and solvated silica nanoparticles 9 nm in diameter as the solid surface. Since the nanoparticles are approximately the same size as the protein, the scattering (about 2%) at 295 nm has little effect on the general spectral data. This technique allows for the study of surface adsorption in solution on virtually any solid material that can be produced in this small colloidal form. Two well-defined proteins with different structural stabilities, bovine serum albumin (BSA) with low conformational stability and lysozyme with high conformational stability, were chosen as models for the initial investigations. The intrinsic fluorescence of the two proteins was analysed prior to and after the addition of the silica nanoparticles. The results demonstrate that BSA produces the largest fluorescence change with both a large fluorescence intensity decrease and a blue shift of 10 nm. Being more structurally stable, lysozyme shows no shift in wavelength, but the adsorption does seem to diminish some of the vibrational relaxation pathways and the relative fluorescence intensity increases.