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Polarity orientation of microtubules and its applications with motor proteins

We have studied integrations of micro/nano machining (MEMS/NEMS) technologies and biomaterials. One of our research directions is to utilize biomaterials in MEMS/NEMS to reveal new functions that could not be achieved by MEMS/NEMS alone. Here a motor protein system will be introduced as a nano actuator. The motility of kinesin and dynein motor proteins has been integrated with MEMS/NEMS or a microfluidic system. Since these motor proteins move on cytoskeletal filaments—microtubules (MTs)—depending on MT polarity, a key technology is to develop methods to orient MT polarities and then immobilize them. We have developed three methods to define MT polarities by (i) shared flow in a microfluidic channel, (ii) nanostructures and (iii) MEMS tweezers. Once MT polarities were oriented and fixed on a chip, they were ready to serve as rails for nano transport by kinesin and dynein motility. The motility was visualized by attaching cargos to motors, where the cargos were microbeads, silicon structures and quantum dots (Q-dots). This nano transport system can achieve a transport distance of up to ∼100 μm, which enables us to focus on the transport of molecules not on bulk molecular flow by conventional microfluidics. Such a bio-hybrid system will be a key factor in realizing nano-scale system integration at the molecular scale.