ABSTRACT
Because of their small size and high thermal conductivity, carbon nanotubes (CNTs) are excellent candidates for exploring heat transfer at the level of individual molecules in biological research. With a view toward examining the thermal regulation of single biomolecules, we here developed single CNTs as a new platform for observing the motile activity of myosin motors. On multiwall CNTs (diameter â¼170 nm; length â¼10 µm) coated with skeletal-muscle myosin, the ATP-driven sliding of single actin filaments was clearly observable. The normal sliding speed was â¼6 µm/s. Locally irradiating one end of the CNT with a red laser (642 nm), without directly irradiating the active myosin motors, accelerated the sliding speed to â¼12 µm/s, indicating the reversible activation of protein function on a single CNT in real time. The temperature along the CNT, which was estimated from the temperature-dependence of the sliding speed, decreased with the distance from the irradiated spot. Using these results with the finite element method, we calculated a first estimation of the thermal conductivity of multiwall CNTs in solution, as 1540 ± 260 (Wm(-1) K(-1)), which is consistent with the value estimated from the width dependency of multiwall CNTs and the length dependency of single-wall CNTs in a vacuum or air. The temporal regulation of local temperature through individual CNTs should be broadly applicable to the selective activation of various biomolecules in vitro and in vivo.