Separation of micro-particles utilizing spatial difference of optically induced dielectrophoretic forces

This paper presents new methods to accurately separate micro-particles with different sizes using optically induced dielectrophoretic (ODEP) forces. It is found that the strength of the ODEP force induced on the hydrogenated amorphous silicon surface is determined by the color, line-width and intensity of the optical beams, which provide an innovative design for particle separation. Two linear-segment virtual electrodes which produced the ODEP forces were firstly defined by illuminating lights onto a photoconductive chip. One moving line and one stationary illuminated line were used to generate a stronger and a weaker ODEP force, respectively. The micro-particles were then continuously pushed forward by the stronger ODEP force. As these lines approached each other, larger micro-particles entrained by the higher ODEP forces were squeezed through the stationary electrode and subsequently separated from the smaller particles. With this approach, continuous particle separation can be automatically achieved within a few seconds. This developed method may be promising for a variety of applications such as cell-based assays and sample pretreatment using micro-particles.