AC Electroosmosis for Lab-On-a-Chip Applications

AC electrokinetics is the study of a particle and fluid motion induced by AC electric fields. In the last decade it has received increasing interest due to its important applications in micro total analysis systems and miniaturized biomedical devices. With the application of very low voltage (~1V_rms), AC electrokinetics can be utilized to control and manipulate particles and fluids at the micro/nano scale, which are very difficult to achieve with existing techniques, such as pressure driven flow.

Through the interaction on ac electric fields and particles/ fluids, ac electrokinetics can be used to sort, separate and filter particles, and to pump and mix fluids. AC electrokinetics can operate at relatively low voltages, which is suitable for integrated lab-on-a-chip systems. This research investigates AC electroosmosis for manipulating nanofluids/ particles with an aim to provide a generic platform for the transport and concentration functions in microfluidic devices. It is envisioned that these concepts can be integrated with life science and biomedical technologies to develop a new generation of labs-on-a-chip, with high-efficiency particle manipulation and sensing, micropumps, and microfluidic mixers.

Two topics are studied in this thesis. One is the trapping/concentration of colloidal and bio-particles. Particle trapping is conducted adjacent to an electrolyte/electrode interface of the gold (Au) electrode pair. We have developed the capability to integrate AC electroosmotic trap and micro-cantilever (MC) in a microfluidic system. By combining both experimental investigation and theoretical analysis, this research work demonstrates a microcantilever particle trap.

The second topic is the transport/mixing of fluids. An original biased AC electroosmotic pump is being developed, and experiments have been performed to prove the concept. Both numerical simulation and pumping experiment is done to optimize the pumping efficiency. The control of the biased AC-EO pumping is also suggested by using the feedback loop.

The thesis concludes with suggestions on how the concepts can be exploited for the development of new strategies for colloidal separation, manipulation for microfluidics and bioMEMS technologies.