Magnetic enhancement of phototaxing catalytic motors.

We use the "stimulus-quench-fuse" (SQF) technique to fabricate micrometer-size colloidal heterodoublets. The doublets consist of silver and magnetic Dynabead microspheres, and the stimulus is a temporal lowering of the pH. The resulting asymmetric colloidal doublets behave as catalytic motors and show self-propulsion and phototaxis under ultraviolet (UV) light in the presence of hydrogen peroxide (H(2)O(2)), by the mechanism of diffusiophoresis. The magnetic heterodoublets show autonomous movement, in random directions, in the presence of H(2)O(2) and UV light, but if an external magnetic field is also present, they align themselves and show a directed motion forming exclusion regions around them. The assembly process described in this Article can be adapted to a wide variety of materials providing a simple, quick, inexpensive, reliable, and scalable approach for the development of synthetic motors capable of performing directed motion and forming exclusion zones and patterns.