The combination of optical with scanning probe microscopy techniques has become a powerful tool for sensing biological events on nanoscale. This combination will significantly contribute to providing new insights to the fields of biosensors, pharmacology, drug discovery, cancer research or nanomedicine over the next few years. In addition to its high resolution imaging capabilities, Atomic Force Microscopy(AFM) has proved invaluable in the area of functional studies as a unique, non invasive technique for measuring the interaction forces between single biomolecules with picoNewton sensitivity. In this study we apply the force measurement features of the Veeco BioScopeTM II to demonstrate the specificity of the interaction between an AFM tip tagged with Pro-Aerolysin (PA) bacterial protoxin, and glycosylphopsphatidylinosithol (GPI)- anchored proteins on living Hela cells.