Magnetic and optical manipulation of spherical metal-coated Janus particles

Spherical colloids with asymmetric surface properties, e.g., 'Janus' particles with two unique faces, are an emerging class of materials that can provide mechanisms for controlling colloidal particle dynamics. Several reports in the literature detail the fabrication of Janus particles as well as their behavior under the influence of external electric, magnetic and optical fields. Here we present an in depth study of the magnetic and optical properties of 10 mu m spherical metal-coated Janus particles, and we demonstrate new mechanisms to control their assembly, transport, and achieve total positional and orientational control at the single particle level. Through the application of external magnetic fields Janus particles formed kinked-chain assemblies. Janus particles can also be transported in rotating magnetic field via hydrodynamic surface effects. Optical fields can control the rotation and clustering of Janus particles at low laser power, but not at higher powers due to the formation of cavitation bubbles and large scattering forces. The unique magnetic and optical properties of Janus particles were leveraged to engineer 'dot' Janus particles that can be utilized to achieve near holonomic control of a single colloid in an optomagnetic trap.