Abstract

Electrokinetic-Based Microfluidic Processes in Lab-on-a-Chip Devices (An Invited Keynote Lecture)

Lab-on-a-chip devices are miniaturized laboratories on a small glass or plastic chip. Generally, a lab-on-a-chip has a network of microchannels, electrodes, sensors and electrical circuits. Electrodes are placed at strategic locations on the chip. Applying electrical fields along microchannels controls the liquid flow and other operations in the chip. These labs on a chip can duplicate the specialized functions as their room-sized counterparts, such as clinical diagnoses, DNA scanning and electrophoretic separation. The advantages of these labs on a chip include dramatically reduced sample size, much shorter reaction and analysis time, high throughput, automation and portability.

The key microfluidic functions required in various lab-on-a-chip devices include pumping, mixing, thermal cycling, dispensing and separating. Basic understanding, modeling and controlling of these key microfluidic functions/processes are essential to systematic design and operation control of the lab-on-a-chip systems. Because all solid-liquid (aqueous solutions) interfaces carry electrostatic charge, there is an electrical double layer field in the region close to the solid-liquid interface on the liquid side. Such an electrical double layer field is responsible for at least two basic electrokinetic phenomena: electroosmosis and electrophoresis. Essentially all on-chip microfluidic processes are realized by using these two phenomena. Therefore it is important to understand interfacial electrokinetic phenomena in order to design and to control the on-chip microfluidic processes.

This presentation will cover the following topics:

1. Electroosmotic Flow

• Basics (modeling and simulation results)
• Flow measurement techniques (1) current method, (2) caged-dye visualization method.
• Solution displacement processes
• Heterogeneous microchannels
• AC electroosmotic flow
• Joule heating effects and measurement techniques

2. Electrokinetic Mixing

• Mixing by T-shaped heterogeneous microchannels (model and simulation results)
• Experimental studies
• Heterogeneous 3D roughness

3. Electrokinetic Sample Dispensing

• Model and simulation
• Experimental studies

4. Particle Electrophoretic Transport

• Single particle in straight channels
• Single particle in T-shaped microchannels
• Multiple particles in a straight channel
• Experimental studies.

Brief Bio

Dongqing Li obtained his Bachelor and Master degrees in China, majoring in Thermophysical Engineering. In 1986 he came to Canada to study Thermodynamics and obtained his Ph.D. degree at the University of Toronto in 1991. In 1993, Dongqing Li joined the faculty in the Department of Mechanical Engineering, University of Alberta, where he obtained tenure in 1997 and was promoted to the rank of full professor in 1999. In that same year he was awarded the McCalla Professorship for research excellence. He later joined the Department of Mechanical and Industrial Engineering, University of Toronto, in 2000 as a tenured full professor. Since 1996, in addition to interfacial phenomena, Dr. Li has started his research in microchannel flow and heat transfer, and began to realize the importance of interfacial electrokinetic phenomena in microscale transport processes. In 2000, Dr. Li developed the Laboratory of Microfluidics at the University of Toronto. His research has focused on various electrokinetic-based microfluidic processes in lab-on-a-chip devices. The research activities in Dr. Li's lab span from theoretical modeling and numerical simulation of a variety of on-chip microfluidic processes to microfluidic flow visualization. Dr. Li's lab is currently developing various lab-on-a-chip devices such as PCR chip for DNA amplification, DNA sensor chip, ELISA chip and Real-Time PCR lab-chip for bacteria and virus detection. Dr. Li has published over 120 papers in leading international journals and nine book chapters. Currently he is writing a book on microfluidics to be published by Academic Press.