NOVEL METHOD OF MEASURING CANTILEVER DEFLECTION DURING AN AFM FORCE MEASUREMENT

A combination of a reflection interference contrast microscope (RICM) and the atomic force microscope (AFM) was used to monitor the cantilev er-surface separation distance during force measurements using the str eptavidin-biotin recognition pairs. The RICM showed that the cantileve r loses contact with the surface before the final rupture of the adhes ive bonds is measured by the AFM detection system. This finding sugges ts that the immobilization of biotin by physisorbed albumin, and subse quent binding of streptavidin might have created a cross-linked protei n network whose cohesion is tested by the AFM cantilever with the immo bilized biotin ligands.