Design of Mechanical and Electrical Properties for Multidirectional Control of Microtubules.

Microtubule (MT)-motor systems show promise as nanoscale actuator platforms for performing molecular manipulations in nanobiotechnology and micro total analysis systems. These systems have been demonstrated to exert a variety of functions, including the concentration, transportation, and detection of molecular cargos. Although gliding direction control of MTs is necessary for these applications, most direction control methods are currently conducted using micro/nanofabricated guiding structures and/or flow, magnetic, and electric field forces. These control methods force all MTs to exhibit identical gliding behaviors and destinations. In this chapter, we describe an active multidirectional control method for MT without guiding tracks. The bottom-up molecular design allowed MTs to be guided in designated directions under an electric field in a microfluidic device. By designing the stiffness and surface charge density of MTs, three types of MT (Stiff-MT, Soft-MT, and Charged soft-MT) with different mechanical and electrical properties are prepared. The gliding directions within an electric field are predicted according to the measured stiffness and electrophoretic mobility. Finally, the Stiff-MTs are separated from Soft-MTs and Charged soft-MTs with a microfluidic sorter.