We have developed a method to detect specific proteins with a high sensitivity using a gel electrophoresis method and force measurement of atomic force microscopy (AFM). Biotinylated proteins were separated by electrophoresis and fixed with cross-linking chemicals on the gel, followed by direct force measurement between the biotinylated proteins on the gel and a streptavidin modified tip of an AFM cantilever. We were able to achieve a high enough sensitivity to detect the picogram order of the biotinylated proteins by evaluating the frequency of the interaction force larger than 100pN in the force profile, which corresponds to the rupture force of interaction between streptavidin and biotin.
