Developing advanced particle manipulation techniques in microfluidic systems

Abstract

Advanced particle manipulation techniques with synergistic effects of low cost, high degrees of controllability, precision, and delicateness have been developed. In particular, the one-dimensional pressure fields in a microfluidic channel device driven by a piezoelectric plate have been investigated. Particles lines were observed along the channel when corresponding resonant frequencies applied. The more complex two-dimensional pressure fields excited by one electrode in the microfluidic channel were also investigated. Single array of particles clumps have been achieved by switching between two frequencies. Additionally, two arrays of particles clumps were observed by sweeping frequency rapidly. Furthermore, particles levitation was observed under certain excitation frequency. Based on the knowledge gained from the microfluidic channel, a microfluidic chamber was conducted in the development of ultrasonic technique. Cavitation bubbles driven by the standing wave generated in the chamber have been studied. Various oscillation modes of the bubbles were also studied. Additionally, the vibrating bubbles as size-based particle selective mechanism were examined. Size varied particles either been attracted (larger particles dominated by Bjerknes force) or repelled (smaller particles dominated by drag force) by the bubble were achieved. As an alternative to the ultrasonic particle manipulation methods, the development of particles forming in lines by capillary flow due to water evaporation has also been demonstrated in this thesis. Particles behaviour has been investigated in a capillary cell formed by a parallel glass slide and a glass cover slip. Particles remaining in hydrated while assembled and harvested in batches were shown. Finally, the establishment of advanced strategies for using the float-sink scheme to selecting single fragile particles has been conducted. A droplet dispensed directly above the selected particle floating on the liquid surface was demonstrated to cause the particle to sink even when the particle was within a floating cluster.