AN INVESTIGATION OF SUBSTRATE AND SAMPLE PREPARATION EFFECTS ON SCANNING-TUNNELING-MICROSCOPY STUDIES ON XANTHAN GUM

Scanning tunnelling microscopy is developing as an important biophysic al tool for the molecular imaging of biological material. In this stud y, the effect of sample deposition technique and substrate employed on the resultant images of a microbial polysaccharide is investigated. S canning tunnelling microscopy topographs of xanthan gum, pipette depos ited and spray deposited onto highly orientated pyrolytic graphite and mica substrates are presented. The use of pipette deposition of the a queous sample solution is shown to result in a xanthan network. In con trast, images of isolated xanthan molecules are obtained when spray de position with glycerol is employed. The effect of these deposition tec hniques on the macroscopic distribution of sample material across subs trates is shown using confocal fluorescence microscopy.