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 and lateral-force microscopy under ambient conditions in air. The results 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 morphology 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 - broadening and double images - were observed and ascribed to tip anomalies. High force loadings and slow repetitive scanning resulted in controlled removal of parts of the TMV structure. Accordingly, it was possible to reveal and image the central core channel of the TMV. The precision and resolution of dissection induced by AFM is currently limited by the shape of the tip, having a 40-nm radius of curvature for standard Si3N4 tips. If is estimated that sharper tips, with a radius of curvature of less than 10 nm, should be able to resolve, non-destructively, the protein subunits in the non-contact mode, and selectively remove single subunits in the contact mode.