  Here we demonstrate a synthetic micro-engine, based on long-range controlled
movement of colloidal particles, which is induced by a local catalytic
reaction. The directed motion at long timescales was achieved by placing
specially designed magnetic capped colloids in a hydrogen peroxide solution at
weak magnetic fields. The control of the motion of the particles was provided
by changes of the concentration of the solution and by varying the strength of
the applied magnetic field. Such synthetic objects can then be used not only to
understand the fundamental driving processes but also be employed as small
motors in biological environments, for example, for the transportation of
molecules in a controllable way.
