IMMOBILIZING AND IMAGING MICROTUBULES BY ATOMIC-FORCE MICROSCOPY

Microtubules isolated from pig brains have been immobilized on an inor ganic substrate for use in AFM studies. The method employs 4-aminobuty ldimethylmethoxysilane and glutaraldehyde to activate a silicon wafer for binding the biopolymer. The covalent bond ensures the positional s tability of the tubules on the substrate, and allows reproducible scan ning probe experiments. Microtubules have been imaged both by atomic f orce and scanning tunneling microscopy, yielding results very similar to electron microscopy. The average apparent height of the tubules is smaller than observed with transmission electron microscopy (25 nm) an d is smaller in buffer solution (10 nm) than in air (15 nm). The biopo lymer surface is softer under buffer than in air. The highest resoluti on was obtained with the tapping mode where surface features as small as 10 nm in X and Y have been resolved. Gold-coated tubules bound on s ilicon have been successfully imaged by STM, while images of uncertain origin were generated for tubules deposited on graphite. It is shown that artefacts imaged on a blank graphite surface can easily be confou nded with collapsed tubules.