Non-contact surface force microscopy for molecular interaction study

Abstract

In order to detect and visualize the electrostatic features of biological macromolecules in a non-contact mode, we have refined the technique of scanning probe microscopy. The forces in the sub-piconewton range between the probe stylus and the sample surfaces have been measured with a gap distance controlled with nanometer accuracy. Images of the electrostatic surface forces of myosin filaments were detected in pure water using positively charged whiskers as cantilever probe tips. The images were consistent with the structure of myosin filaments that have a bipolar spindle shape; they were charged with a great number of negative charges in the central bare zone compared with the rest of the filament. Thus, in this non-contact mode, the electrostatic features of the protein surface rather than the surface topography were measured. This method has been further extended to measure forces exerted between protein molecules. Long-range interaction between kinesin and microtubules has been examined. It is likely that long-range attractive forces, in the order of several nanometers, exist between kinesin and microtubules. [DOI: 10.1380/ejssnt.2005.46]