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Acknowledgement: 

The material presented here is based upon work supported by the National Science Foundation under Grant No. 0448896.

Principal investigator: Prof. Jayne Wu 

A Brief Overview of Electrokinetics

A microfluidic chip should have following functions: mixing, pumping, concentration step to assist detection, etc., as shown schematically here. As device dimension scales down, pressure driven flow becomes increasingly inefficient due to high surface-volume ratio. In contrast, electrokinetics is gaining popularity as a microfluidic actuation mechanism, due to its no moving parts and easy implementation. Traditional electrokinetic pumping requires applying high DC voltage across the microchannel, and the electric field drives the mobile charges at the fluid/channel interface (i.e. electroosmosis) to transport fluid. High voltage causes bubble generation and pH gradients from electrochemical reactions. To minimize these adverse effects, AC electrokinetics (ACEK) has emerged recently for on-chip pumping and particle manipulation for its low voltage operation.

ACEK investigates the behavior of particles in fluid and the motion of electrolytic fluids when they are subjected to AC electrical fields. Charges are induced in the bulk of the fluids where there is an interface (e.g. electroosmosis) or gradients in fluid attributes (e.g. electrothermal effect). Because the electric fields and induced charges in fluid change polarity simultaneously, steady (not oscillatory) fluid motion can be generated in ACEK. There are mainly three types of ACEK phenomena, dielectrophresis (studied since 1991), AC electroosmosis (since 1999, our group initiated “biased ACEO”) and AC electrothermal effect (our group is the first to have developed ACEK micropumps). ACEO is mainly effective for low-conductivity fluid (e.g. water), thus limiting its application in lab-chips. We have developed capabilities for conductive fluids, making an important step towards practical EK devices.

ACEK can also manipulate micro/nano particles in the fluid, which include DNA, protein molecules, virus, bacteria, plant and animal cells, and inorganic particles. To detect low concentration bioparticles, a concentration step is necessary to increase particle count to a critical mass at the detection sites. ACEK is the only known on-chip method to collect particles in a short time. My group prototyped a first in-situ microcantilever particle trap (experimented on 200nm to 1µm particles), and we are extending it to protein and DNA concentrating.

My group is at the forefront of ACEK research, contributing to both its fundamental understanding and practical applications. In this burgeoning field, only imagination is the limit.

Selected Projects Descriptions:

Current Projects:

· 2005 National Science Foundation (NSF) CAREER Award

“CAREER: Developing Asymmetric-Polarization AC Electroosmosis for Lab-on-a-chip”

06/01/2005 – 05/31/2010.

· User projects at the Center for Nanophase Materials Sciences, ORNL

1. “Electrokinetic Labchip for Rapid Detection of Low-Concentration Micro/Nano-Size Bioparticles”

2. “Fabrication Of Nano-Injection Needles For Neural Pathway Study In Mice”

· DOE Retinal Prosthesis Research

“PDMS (Polydimethylsiloxane)-Based Microelectrode Chips for Retinal Prosthesis”

11/03/2005-11/02/2006.

· Joint Laboratory Directed Research and Development

“ACEO Synthesis of Nanocomposite Dielectrics/Polymer: Applications for Electric Power Grid”

· NSF CTS

“Rate-Based Sensor Development for Advancing Heat Transfer Measurements”

04/15/2006 – 04/14/2008

· Oak Ridge Associated University

Integration of Particle Trapping with Cantilever Arrays for Ultra-High Sensitivity Chemical and Biological Agent Detection

Past Projects:

· Development of Instructional MEMS Laboratory, Engineering Fee, CoE, UTK, $203,000, with M. Mahfouz, FY 2005-2006.

· Electrokinetic Labchip for Rapid Detection of Low-Concentration Micro/Nano-Size Bio-particles, Oak Ridge National Laboratory (ORNL), Center for Nanophase Materials Sciences (CNMS), 01/03/2005-11/30/2006.

· Fabrication of Nano-Injection Needles for Neural Pathway Study in Mice, ORNL, CNMS, 12/08/2005-11/30/2006.

· Inductive Links with Integrated Receiving Coils for MEMS and Implanted Applications

· Fabrication, Characterization and Simulation of Power AlGaInP/GaAs HBTs