Optoelectronic tweezers (OET) provides a non-invasive, low-power, optical manipulation tool for trapping, transporting, and separating microparticles, cells, and other bioparticles. The OET device uses a photosensitive layer to form "virtual electrodes" upon exposure to light, creating non-uniformities in an applied electric field. The electric field gives rise to a force known as dielectrophoresis: microparticles move as a result of the non-uniformities in the electric field imparting unequal forces on the induced dipoles of the particles. These virtual electrodes can be actuated with low optical intensities, enabling the use of incoherent light sources and direct imaging techniques to create optical manipulation patterns in real-time. In this paper, we demonstrate OET operation on live cells, including the trapping and manipulation of red and white blood cells, and the automated collection of HeLa cells. Automated size-based sorting is performed on a mixture of 15- and 20-μm-diameter polystyrene beads, and dielectric property-based separation is used to differentiate between live and dead white blood cells.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.