Imaging of proteins adsorbed on self-assembled monolayers by atomic force microscopy in liquid

Atomic force microscopy (AFM) imaging of proteins adsorbed on Au(111) substrates was examined. When Au(111) was modified with 4-mercaptopyridine self-assembled monolayers (SAM), uniformly adsorbed hemoglobin molecules were observed on the substrate in a physiological buffer solution. In contrast, very few molecules were observed on octadecanethiol SAM. When the bare Au(111) was used without surface modification, unclear AFM images were obtained although protein molecules might have been adsorbed. The results suggested that the adsorption phenomenon of metalloproteins is strongly affected by surface modification of the gold substrate. In addition, our data indicated that the adsorbed metalloproteins on SAM could be successfully observed by tapping mode AFM in physiological solution without chemical fixation of protein molecules.