Spectroscopic and microscopic examination of protein adsorption and blocking of non-specific binding to silicon surfaces modified with APTES and GOPS

X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) were applied to characterize two series of silicon nitride surfaces, modified either with (3-aminopropyl)triethoxysilane (APTES) or (3-glycidoxypropyl)trimethoxysilane (GOPS), prior to and after immobilization of rabbit gamma globulins (rIgG) at different concentrations and blocking with bovine serum albumin (BSA). Higher rIgG amount was adsorbed to surfaces silanized with APTES rather than GOPS, resulting in different behavior to subsequent blocking. There was no increase in total protein surface density due to blocking with BSA for surfaces with already high protein coverage. Apparently, BSA molecules were partly exchanged with rIgG ones, in case of APTES and higher rIgG concentrations, or attached to free surface sites, for GOPS modified surfaces.