Measurement of the mechanical properties of living cell using micro hand and developed AFM system

In this paper, the mechanical properties of yeast cell are determined by means of the developed two-fingered micro hand and an atomic force microscope (AFM). The micro hand has excellent absolute positioning accuracy after the elaborated calibration, and is typically capable of obtaining less than several hundred nanometer of positioning accuracy by human tele-operation. The authors also developed an AFM system of our own composition. The AFM consists of a laser diode module, a cantilever, a 4-segment photodiode and output circuit. The task to measure the mechanical properties of cells include moving of the fingers from the home position to the target object (cell), then picking and grasping it, moving it to a target position (AFM tip), and finally pushing it against the cantilever tip. However, since it is difficult to stabilize the sample, the authors utilized the capillary phenomenon, i.e. the liquid inside the tube-shaped object ascends the inner wall in order to stabilize the sample strongly. And force-indentation relation was obtained applying a force to individual yeast cells by moving the sample to the cantilever tip. Force is automatically calculated from the cantilever deflection measured with a laser beam and a quadrature photodiode, while indentation is obtained from the difference between the movement of the micro hand and that of the cantilever tip caused by cantilever deflection. The mechanical properties of yeast cells is finally determined using the produced force-indentation curves, the Hertz model and FIEL (force indentation to equal limits) mapping, which is an analytical way for determining relative microelastic properties from force volumes of viscoelastic materials.