Analysis of force curves obtained on the live cell membrane using chemically modified AFM probes

Force curves were obtained on the live cell surface using an atomic force microscope mounted with a modified tip with the bifunctional covalent crosslinker, disuccinimidyl suberate, which forms a covalent bond with amino-bearing molecules on the cell surface. A ramp delay time of 1.0 s was introduced before the start of the retraction regime of the force curve to increase the stationary reaction time between the crosslinkers on the tip and the amino groups on the cell surface. While live cell surface responses to forced contact with a non-functionalized tip rarely showed evidence of tip-cell interaction, those obtained with modified tips gave clear indication of prolonged adhesion which was terminated by a single step release of the tip to its neutral position. Under the given experimental conditions of this work, 58% of a total of 198 force curves gave only one jump and 70% of those with one jump gave the final rupture force of 0.45+/0.22 [corrected] nN. The result emphasized the uniqueness of the observed mechanical response of the cell surface when probed with chemically modified tips.