A metallic replica/anchoring technique for scanning tunneling microscope or atomic force microscope imaging of large biological structures

Abstract

We describe and give results for a metallic replica technique in which biological structures are first deposited on a flat graphite substrate and then overcoated with a thick metallic film. The metallic film is then peeled off the graphite, and its underside is imaged by the scanning tunneling microscope (STM), which shows indentation-type replicas. We have used the technique on the cell sheath of the bacterium methanospirillum Hungatei, and find that the surface detail of the replica image is as good as that for a metal-coated sheath. We also find that the biological structures stay in the indentations during the peeling-off process, which gives the possibility of imaging bare structures that would normally be pushed along a flat substrate by the STM or atomic force microscope (AFM) tip.