Fig. 2: Particle locomotion under various conditions.

Image sets a–c show the trajectory of the random motions of the CNT-bot at different time intervals (labelled on the image) in a hydrogen peroxide bath (12%, v/v), water, and a 0.5 M hydrochloric acid bath, respectively. Image set d shows the trajectory of the CNT-bot in a 0.5 M aqueous solution of sodium bicarbonate. Image sets e–g show the trajectory of the directional motion of the CNT-bot at different time intervals when a concentration gradient was established by dripping acid in a water bath, alkali in a peroxide bath, and bicarbonate in a bath of water. The arrowheads on the images indicate the direction of the movement of the motor. The concentration gradient is indicated by the bromophenol blue, phenolphthalein, and indicators in image sets e–g, respectively. Image set h shows the particle trajectory at different time intervals driven by an externally applied magnetic field. In these experiments, the motor size was ~180 μm to ~300 μm.