Evanescent-wave cavity ring-down detection of cytochrome c on surface-modified prisms

Adsorption kinetics and molecular interactions on different surface interfaces are studied by means of evanescent-wave cavity ring-down spectroscopy, using total internal reflection surfaces onto which different self-assembled monolayers are covalently attached. The adsorption of cytochrome c (a positively charged, spherical heme protein) to a negatively charged bare silica surface, as well as to C18-coated (hydrophobic) and C3NH2-coated (positively charged) silica have been studied. It is experimentally verified that these surface layers do not interfere with the sensitive measurement of adsorbed cyt c monolayers using the evanescent wave in a ring-down scheme. Attaching monolayers covalently to the silica total internal reflection surface is a first step towards the development of a biosensor that makes use of immobilized biomolecules for specific detection of analytes in solution.