Autonomous transport and release of bacterial cells by self-propelled micromotors were achieved. The motors consisted of zinc and platinum hemispheres formed on polystyrene beads and moved as a result of simultaneous redox reactions occurring on both metal ends. The highly negative redox potential of zinc enabled the selection of a wide variety of organic redox compounds as fuels, such as methanol and p-benzoquinone. The movement of motors was observed in solutions of fuels. To realize autonomous capture, transport, and release of cargo, a self-assembled monolayer (SAM) was formed on the platinum part of the motor. This SAM could be desorbed by coupling the reaction with the dissolution of zinc, which could also be controlled by adjusting the concentration of Zn(2+) ions. Escherichia coli (E. coli) cells were captured by the motor (due to hydrophobic interactions), transported, and released following SAM desorption at the mixed potential.

3D control of the motion of self-powered micromotors is demonstrated using AC electrokinetics by applying an AC electric field on indium tin oxide transparent electrodes.

Two self-propelled micromachines were fabricated with gold/platinum micromotors that exhibit simple translational motion in a fuel solution. In each one, two micromotors were connected with a joint of polymer tube formed by stacking cationic poly(allylamine hydrochloride) (PAH) and anionic poly(acrylic acid) (PAA) using a layer-by-layer technique. A bent structure was created by making one longitudinal side of the joint more swellable with alkaline treatment. The joint containing fewer PAA/PAH bilayers was flexible and allowed a larger range of Brownian angular fluctuation. In the fuel solution, bending and stable rotation were observed for the micromotors tethered with soft and rigid angled joints, respectively. The radius and angular velocity of the rotation depended on the angle of the joint. Such tethered micromotors can be used to realize sophisticated micro/nanomachines for microscale surgery and drug delivery.

Zinc/platinum (Zn/Pt) bimetallic micromotors have been developed. They moved based on the reduction of fuel compounds such as bromine, p-benzoquinone, and methanol at the surface of the Pt and the oxidation (dissolution) of Zn that occur simultaneously. The redox potential of Zn 2+ /Zn is very negative and was advantageous to cause the redox reactions. The motion of the motor and the reactions that occurred on the surface were investigated. With test motors containing Ni, it was revealed that the Zn/Pt motors showed almost unidirectional motion to the Zn side. Toxicity of Zn 2+ is relatively lower than that of other metal ions. Also, the motor features the use of mild compounds such as methanol that are not harmful to tissues or organisms as their fuels.

Three‐dimensional control over the motion of self‐powered Janus micromotors is demonstrated by T. Honegger and co‐workers using AC electrokinetics, by applying AC electric fields on transparent indium‐tin‐oxide electrodes. On page 5630, they show how micromotor direction can be regulated for single or collective motion, applicable to in vitro cell manipulation or drug delivery by chemically modifying micromotors without complicated equipment.