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 cantilever-surface separation distance during force measurements using the streptavidin-biotin recognition pairs. The RICM showed that the cantilever loses contact with the surface before the final rupture of the adhesive bonds is measured by the AFM detection system. This finding suggests that the immobilization of biotin by physisorbed albumin and subsequent binding of streptavidin might have created a cross-linked protein network whose cohesion is tested by the AFM cantilever with the immobilized biotin ligands.