Liquid metal electrodes enabled cascaded on-chip dielectrophoretic separation of large-size-range particles.

The separation of large-size-range particles of complex biological samples is critical but yet well resolved. As a label-free technique, dielectrophoresis (DEP)-based particle separation faces the challenge of how to configure DEP in an integrated microfluidic device to bring particles of various sizes into the effective DEP force field. Herein, we propose a concept that combines the passive flow fraction mechanism with the accumulative DEP deflection effect in a cascaded manner. This concept places DEP deflection segments and bypass outlets alternately. Each DEP deflection segment is configured with an array of side-wall liquid metal electrodes to exert effective DEP forces on the particles of a suitable size range. After each DEP deflection segment, the passive bypass flow fraction mechanism diverts part of the sample flow and target range of particles through the bypass outlet. Simultaneously, this flow fraction brings the remaining particles closer to the electrodes in the subsequent DEP deflection segment, causing the next size range of particles to deflect under effective DEP forces and thus making them separable. Repeating this process, particles would be separated from the bypass outlets one by one in the order of reducing size ranges. We present the concept design and modeling, and prove the concept through separating five different particles ranging from 16-0.5 μm mixed together to mimic blood composition, providing a powerful platform for separating multiple particles in diverse biomedical applications.