IMAGING AND NANO-DISSECTION OF TOBACCO MOSAIC-VIRUS BY ATOMIC-FORCE MICROSCOPY

Tobacco mosaic virus (TMV) has been deposited on freshly cleaned mica substrates. The topography was investigated by contact, non-contact an d lateral-force microscopy under ambient conditions in air. The result s were in accord with known dimensions of TMV (i.e. 18 nm in diameter and 300 nm in length). However, convolution of tip shape with TMV morp hology resulted in an apparent width of 80-140 nm in the lateral plane , a factor of 4-7 greater than the known diameter. Other artefacts - b roadening and double images - were observed and ascribed to tip anomal ies. High force loadings and slow repetitive scanning resulted in cont rolled removal of parts of the TMV structure. Accordingly, it was poss ible to reveal and image the central core channel of the TMV. The prec ision and resolution of dissection induced by AFM is currently limited by the shape of the tip, having a 40-nm radius of curvature for stand ard Si3N4 tips. If is estimated that sharper tips, with a radius of cu rvature of less than 10 nm, should be able to resolve, non-destructive ly, the protein subunits in the non-contact mode, and selectively remo ve single subunits in the contact mode.