Electrophoretic Mobility of Nano-sized Actin Filaments in Biomolecular Device

The aim of this study is to clarify the electrokinetic properties of negatively-charged actin filament (F-actin), one component of actomyosin known as a biomolecular motor. Here we studied the directional movement and velocity of suspending F-actin under DC electric fields. The movement was observed above the SiO2-coated microscopic slide with two chrome electrodes, in which a gap between electrodes ranged from 1 to 10 mm and the voltages were applied at 0.5 to 10 V. When the voltage exceeded 3 V regardless of the gaps, F-actin moved toward a positive electrode. The velocity was directly proportional to the voltage for all gaps of 1, 2, 5 and 10 mm. At less than 3 V, F-actin stayed at the same point, i.e. the Brownian motion. When the gap narrowed from 10 to 1 mm, the velocity increased. Four gaps of 1, 2, 5 and 10 mm had the similar velocity as a function of electric field corresponding to electrophoretic mobility. The velocity was not significantly affected by changes in pH from 6.5 to 8.4 as well as in ionic strength from 25 to 100 mM KCl. The result indicates that the electrode fabrication of the SiO2surface is useful for the field-induced control of the velocity and direction in F-actin. It would provide the kinetic properties of F-actin for the possible combination of actomyosin motility with MEMS.