Xiaolu Zhu

Frequency-dependent behaviors of individual microscopic particles in an optically induced dielectrophoresis device

An optoelectronic microdevice is set up to drive single microparticles and a maximum synchronous velocity (MS-velocity) spectrum method is proposed for quantifying the frequency-dependent behaviors of individual neutral microparticles from 40 kHz to 10 MHz. Dielectrophoretic behaviors of three types of microparticles are investigated under the optically induced nonuniform electric field. Different MS-velocity spectra for the three different particles are experimentally found. Numerical calculations for the MS-velocity spectra of polystyrene microparticles are performed. The spectrum of the MS-velocities for a specific particle is mainly determined by the particle inherent property and the electric characteristics of the device. Moreover the experimental and the numerical MS-velocity spectra are compared to be accordant. Based on the dielectrophoretic (DEP) behaviors of the particles under a nonuniform electric field, microparticles can be finely characterized or distinguished according to their distinct MS-velocity spectra.

Novel design of multiphase optoelectronic microfluidic device for dielectric characterization of single biological or colloidal particles

A novel multiphase optoelectronic microfluidic device (MOMD) based on optoelectronic effect and multiphase dielectrophoresis (DEP) is designed by our group for accurate dielectric characterization and flexible manipulation of individual microscopic particles, which overcomes the drawback that the conventional microfluidic devices cannot accurately characterize single bio-particles. The microelectrode layer of MOMD integrating quadrupole electrodes and spiral electrodes is designed for the dielectric measurements of micro particles, while the photoconductor of MOMD is designed for the dynamic manipulation of the particles. The numerical simulation is implemented for the distribution of time-averaged dielectrophoretic force, torque and particle velocities. The results agree well with the experiments in the literature. The numerical results show that both real and imaginary parts of particle effective polarizability α̃ determining the particle characteristics can be calculated simultaneously through measuring the traveling velocity Vr of the particles, which is simpler than previous methods. Moreover, the results also show that the particle travelling velocity, suspension height and electrorotation velocity can all be measured accurately for dielectric characterization with the help of light-induced DEP mechanism integrated on the MOMD. The MOMD needs not the expensive optical tweezer system for single particle manipulation, and therefore has a greatly low cost.

Automatic separation of microscopic particles via optoelectronic chip and associated platform

An effective technique for automatic separation of microscopic particles through an optoelectronic micro device is experimentally demonstrated. This technique is realized through the scanning of light patterns at a certain frequency of the actuating signal for this device. This electrodeless technique can dynamically reconstruct the distribution of electric field, which overcomes the drawback that conventional microfluidic devices need costly and rigid microelectrodes or microchannels. The influences of the signal voltage and the width of the micro light line on the pollen particle velocity are discussed through experiments and simulations. The conclusion is drawn that the optimal frequencies for the separation of pollen grains with different properties range from 500 kHz to 1 MHz, and increasing the ac signal voltage and the light line width are able to increase the saturating velocity of pollen particles. Furthermore, increasing light linewidth is better than increasing the voltage under the precondition that separation accuracy is guaranteed.