Ac Electrokinetics and Its Applications in Lab-on-a-Chip (LOC) and Microfluidics Devices

AC Electrokinetics and its Applications in Lab-On-a-Chip (LOC) and Microfluidics Devices

Dr. Nazmul Islam

Abstract

Recently AC electrokinetic (ACEK) has emerged as a promising strategy to capture, manipulate and transport bio/nano-particles in microfluidic devices. This presentation focuses on AC electrokinetic phenomena, specifically AC electroosmosis (ACEO) and its new development by using biased technique. Using an array of microfabricated planar interdigitated electrodes, the electrokinetic flows and particulate assembly patterns on electrode surface are examined. As the electrokinetic device involves no moving parts, it is simple and robust, which makes it an excellent candidate for micro/nano-system integration. Integration of micro-cantilever with ACEO system in the microfluidics channel and bio/nano-particle quantification will also be discussed. 

One of the most notable methods for improving ACEK microflows is the design of an orthogonal electrode pair that accentuates the non-uniformity in the electric field and, as a result produces stronger net flows at lower voltages. Orthogonal electrodes also have been reported to produce high velocity fluid flow when excited by AC signals, showing potential for micro-pumping applications. Breaking the symmetry of electric fields in the electrode pair produces a unidirectional flow [1] which is salubrious for pumping. As many research groups believe that the Manipulation of microfluidics and particles can be effectively done by ACEK technique, the current research work in our lab involves in designing a multifunctional system to manipulate the particles to improve the binding process and the fluid flow. This research also explicates the AC electrokinetic processes such as capacitive electrode polarization, Faradic polarization and the AC electrothermal effect, to better explain the directional flow patterns and their role in manipulating the microfluidics. Different flow patterns were obtained by varying the level and frequency of AC potential. In these experiments it is shown how orthogonal electrode pattern can be optimized and used as a multifunctional system. Like many other research groups flow reversal has been observed which can act as a value to control the fluid flow. Systematic fabrication of orthogonal electrodes with proper sealing and chamber space can be used to build chips and Lab-on-Chip devices. As the orthogonal electrode pair showed potential for pumping a conventional mechanical pump can be replaced with ACEK driven components for integration into lab-on-a-chip applications.

This presentation will also focus on the development of bi-directional AC electroosmotic micropump. Our proposed biased ACEO micropump will combine the DC and AC (alternating current) signal with the electroosmosis technique for surface fluid flow control. The resulting pump will be capable to produce bi-directional flow and will be highly controllable.  In addition, this micro pump is expected to require very small AC voltage for operation and is compatible with microfabrication technology. The presentation will conclude with the future research work on microsystem integration with MEMS devices.