We have developed a practical method to control the number of attaching biomolecules to an AFM tip. Monolayer of OEG that has little interaction with some biomolecules was self-assembled on tips. Electric pulses were used to oxidize a patch of OEG monolayer on tip and generate COOH groups for further linking at the activated area. The surface groups were detected by chemical force titration. The total numbers of molecule bound on the tip was examined by the studies of biotin/streptavidin system.