Fabrication of various tip-size AFM probes for evaluating single-molecular retraction force between actin and anti-actin

The authors fabricated a probe tip with various sizes and examined the size dependency of the probe tip on the distribution of retraction forces between actin and anti-actin. Probe tips of various sizes were fabricated by two-photon polymerization methods on a micro cantilever of an atomic force microscope (AFM). The authors succeeded in fabricating a spherical tip having a smooth surface and the tip size varied between phi 0.8 and 5.5 microm. Anti-actin was immobilized on the fabricated probe tips and force curves were measured against an actin-immobilized mica substrate by AFM to analyze the retraction forces. The histograms of retraction forces showed that the single-molecular retraction force between actin and anti-actin was ca. 350-400 pN. It was observed that the average retraction forces for each tip size correlated with the square of the tip radius.