Hydrogen bonding molecules and their effect on scanning tunneling microscope image contrast of covalently immobilized protein molecules

The enzyme catalase has been covalently bound to a self-assembled monolayer adsorbed to a gold substrate using an organic solvent-based attachment method. The enzyme was shown to remain catalytically active after immobilization to the surface. Methanol was adsorbed to the protein surface under conditions of controlled vapor pressure. The effects on the scanning tunneling microscope (STM) image contrast of covalently immobilized catalase were recorded under varying conditions of partial pressure: from the dry state to a 100% methanol saturation level. A significant increase in image contrast was observed as the amount of methanol bound to the protein increased, The data obtained in this study have been compared to contrast changes observed upon protein hydration. which like methanol, also increases protonic surface conduction through surface hydrogen bonding. The method described here can be used for the rapid and facile identification of adsorbed biological material that may not be immediately discernible under ambient STM imaging conditions. (C) 1996 American Vacuum Society.