Scanning tunneling microscopy of biomolecules

We have used STM to study a range of biological molecules. The necessity of immobilizing the molecules on the surface was recognized and achieved by the formation of ordered layers or by the addition of chemical groups which strongly adsorbed to the graphite substrate. Clear images of the helical structure of the synthetic polypeptide poly y-benzyl-L-glutamate were obtained. Images of protein molecules isolated from wheat were found to be consistent with the rare β-spiral conformation. The binding of the mutagen ethidium bromide to DNA was also studied and images of the cyclic glucan β-cyclodextrin, tosylated to improve adsorption of the molecule to graphite, were also obtained. Although the contrast mechanism is unclear in some of these examples, these results suggest that STM can be applied successfully to a wide range of biomolecules.