Studies of covalently immobilized protein molecules by scanning tunneling microscopy: the role of water in image contrast formation

Protein molecules have been immobilized on gold surfaces using a novel covalent attachment technique. The naked molecules have been imaged with the scanning tunneling microscope (STM), and the effects of protein dehydration on STM image contrast have been investigated. A reversal of image contrast is observed upon reduction of the relative humidity inside the STM chamber from 33% to 5%. It is concluded that water plays a crucial role in the formation of the STM image of the protein molecules under ambient conditions.