Construction of Scanning Tunneling Microscope for the Study of Interacting Biological Molecualr Systems and their Preparation

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WE have developed a scanning tunneling microscope (STM) that works on biological materials under clean and defined conditions. Following the great success of STM is the field of surface science, many attempts have been made to test its use in bio-medical field with limited success. The difficulty lies in both the poor electrical conductivity of thick organic and biological samples and often poorly reproducible results from various research groups. The first problem is inherent to the physical nature of the target material but the second is often the measurement done under less well defined environment such as atmospheric condition with unspecified humidity. The apparatus we developed here has an STM scanning unit in a large chamber where not only the STM operation but also application of wet biological samples on a freshly prepared substrate surface can be done. In this way, there is little possibility that the sample is contaminated with impurity in air. Using this apparatus and new software, we have imaged DNA, proteins, bacteriophages, viruses and cell membranes under clean and well defined conditions. Thick samples such as phages and viruses must be coated with thin layr of metal to be observed by STM.If the thickness of such metal coating is thin enough, we could identify some structural details with the information on the surface topography. We are now in the position to fully apply the completed apparatus to the topographical studies of biological surfaces.