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 μm 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.
Thin ferromagnetic film patterned into isolated islands is used to direct assembly of superparamagnetic colloidal particles into two-dimensional arrays. Ferromagnetic islands positioned under a template of micro-wells are shown to promote highly regular 2D arrays, while external uniform magnetic field is used to bias the particles to attract or repel from the exposed end of the ferromagnetic islands. A theoretical analysis on the interactions between superparamagnetic colloidal particles with the template and external uniform magnetic fields is also presented.