Development of Moving Micro-Machines That Use Hydrogen Peroxide and Glucose as Fuels

We are developing the micro-machine moving by converting chemical energy to mechanical energy to apply the micro-machine to drug delivery system. Our micro-machines were fabricated with two steps. In the first step, Au metal was electrochemically deposited on a Ag wire, following by the chemical dissolution of the Ag wire in strong acidic solution. In second step, inner walls of the cylinder of Au metal obtained with the dissolution process were used for fixing the glucose oxidase and catalase, that work in pair to convert chemical energy of glucose to mechanical energy of O₂ gas formation, by adsorbing them with layer-by-layer method using polymer material (Fig. 1). The O₂ gas formation becomes driving force of the micro-machine. We made two type of micro-machine with metal and polymer cylinders (Fig. 2). The time courses of metal cylinder type of micro-machine were monitored for 1 min (Fig. 3). When the enzyme of catalase was fixed on the inner wall of the metal cylinder, the micro-machines moved actively by the formation of O₂ bubbles with oxidation of H₂O₂ on catalase. In the solution in the absence of H₂O₂, the micro-machine did not move except for slight movement due to natural convection of the solution. In order to remove the bubbles of O₂ from the inner wall of the metal cylinder and to increase the moving rate of the micro-machine, a surfactant of TritonX-100 was added to the test solution where the micro-machines are moving. In addition, the micro-machine moved to the source of H₂O₂ (Fig. 4(a)), that is the micro-machine go up the gradient of H₂O₂ concentration. In the photographs of Fig.4, the injection points of H₂O₂ were located in the left side of the photographs. On the other hand, the micro-machine which was not modified with catalase did not move(b). Therefore, the moving direction of the micro-machines that we designed can be controlled by the gradient of chemical materials that produce the O₂ bubbles by converting chemical energy to mechanical energy.