The atomic force microscope (AFM) has become a valuable tool for cell biologists. Although the AFM has been mainly used as an imaging device, it has recently found several other applications where it is used to study the mechanical response of biological samples against a local application of force. In this paper, we showed that the AFM could be used to extract cell surface proteins using covalent crosslinks between a modified tip and the cell surface for later identification of the extracted proteins and lipids. A series of experiments were performed to extract proteins from a cell surface by using amino reactive, bifunctional covalent crosslinkers between an AFM tip and living Balb 3T3 cells. Results showed that the frequency of the rupture force between modified Si₃N₄ tips against the cell surface was high between 100 and 600 pN. The average rupture force was significantly less than the force to break the covalent bond system (1.6 - 1.7 nN), indicating that whatever that was bound to the tip through its amino group was extracted from the cell surface. A similar method was applied to living cells using a modified tip with specific ligand molecules, and it has been shown that receptors on the cell surface could be located and mapped (Kim, Osada and Ikai to be published).

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