IMAGING 2-DIMENSIONAL ARRAYS OF SOLUBLE-PROTEINS BY ATOMIC-FORCE MICROSCOPY IN CONTACT MODE USING A SHARP SUPERTIP

A sharp tip with high aspect ratio is required for imaging biological macromolecules by atomic force microscopy (AFM), A tip with the end ra dius of curvature less than 3 nm has been reproducibly fabricated by m eans of electron beam deposition (EBD) in a field-emission scanning el ectron microscope. Two-dimensional protein arrays of ferritin and cata lase, prepared at air/water interface and transferred onto silicon waf er, could be imaged both in air and in water by AFM using this sharp E BD-tip in contact mode. The negative staining preparation conventional ly used in transmission electron microscopy of protein was applied and shown to be quite effective in fixing the protein arrays for the AFM imaging in air. Individual molecules of ferritin and catalase were vis ible in the two-dimensional arrays. Also, imaging in water of these pr otein arrays presented molecular images clearer than in air, due proba bly to the absence of the adhesion force and the resulting weak latera l force during scanning. These images convince us of the capability of this supertip for AFM studies of biological molecules under aqueous c onditions. (C) 1998 Elsevier Science B.V. All rights reserved.