Dielectrophoretic and Thermophoretic Control of Particles with Laser-Illuminated Electrode Arrays Embedded in Microfluidic Channels

Abstract Metal electrodes integrated into microfluidic channels are used to manipulate particles through a combination of dielectrophoretic and thermophoretic forces. The electrode arrays are milled into a thin metal film disposed in a microfluidic channel to precisely position the arrays within the fluid flow. Upon laser illumination, these electrode arrays exert forces on nearby particles that are coupled with microfluidic flow. The primary modes of particle-electrode interactions are lateral attraction, particle capture, edge confinement, and particle repulsion. Finite element analysis models reveal that metal electrodes generate electric field gradients toward the electrode that oscillate at the laser frequency, thereby exerting an attractive dielectrophoretic force on particles. Heating of the electrodes with the laser creates thermophoretic temperature gradients that repel particles. The balance between attractive and repulsive forces are quantitatively mapped across laser intensities and fluid velocities. At lower intensities and velocities, particles are attracted to and trapped on the electrode arrays. At higher intensities and velocities, the thermophoretic force exceeds the dielectrophoretic force, and particles are repelled from the electrodes. Because the dielectrophoretic and thermophoretic forces are easily tuned, the electrode arrays can be controllably switched across operational modes.