COMPARISON OF SCANNING TUNNELING MICROSCOPY AND TRANSMISSION ELECTRON-MICROSCOPY IMAGE DATA OF A MICROBIAL POLYSACCHARIDE

The study of biological material by scanning tunnelling microscopy has led to a need for critical validation of the resultant data. We present here a comparison of scanning tunnelling microscopy images and electron micrographs of a microbial polysaccharide. Xanthan gum in a glycerol solution was sprayed onto mica discs and coated with a platinum/carbon conducting layer and a carbon backing layer. The ability of the scanning tunnelling microscope to image replicas as prepared for electron microscopy is demonstrated. The images of isolated xanthan molecules have comparable contrast to electron micrographs and in addition, contain directly available 3D data. The implications of these results, for future progress in sample preparation for STM studies, are discussed. Further images of xanthan, coated only with platinum/carbon, are used to illustrate that the resolution can be improved by a reduction in the grain size of the coating.