Evaluation of the actin cytoskeleton state using an antibody-functionalized nanoneedle and an AFM.

A cell diagnosis technique was developed, which uses an Atomic Force Microscope (AFM) and an ultra-thin AFM probe sharpened to a diameter of 200 nm (nanoneedle). Due to the high aspect ratio of the nanoneedle, it was successfully inserted into a living cell without affecting its viability. Furthermore, by functionalizing the nanoneedle with specific antibodies and measuring the unbinding forces ('fishing forces') during evacuation of the nanoneedle from the cell, it was possible to measure specific mechanical interactions between the antibody-functionalized nanoneedle and the intracellular contents of the cell. In this study, an anti-actin-antibody-functionalized nanoneedle was used to evaluate the actin cytoskeleton state in living cells. To examine the effect of cytoskeleton condition on the measured fishing forces, the cytoskeleton-disrupting drugs cytochalasin D (cytD) and Y-27632 were used, showing a marked decrease in the measured fishing forces following incubation with either of the drugs. Furthermore, the technique was used to measure the time course changes in a single cell during incubation with cytD, showing a gradual time-dependent decrease in fishing forces. Even minute doses of the drugs, the effects of which were hardly evident by optical and fluorescence methods, could be clearly detected by the measurement of nanoneedle-protein fishing forces, pointing to the high sensitivity of this detection method. This technique may prove beneficial for the evaluation of cytoskeleton conditions in health and disease, and for the selection of specific cells according to their intracellular protein contents, without the need for introduction of marker proteins into the cell.