Electrokinetic Micromixer

Project

Micro-Systems & Control Laboratory, NTHU

Objectives:

For many Bio-medical applications targeted for drug delivery, DNA hybridization, and PCR amplification, rapid and homogenous mixing of two or more fluid species is required. For macroscopic fluidic devices, turbulent flow is available to enhance this mixing process with an acceptable mixing time period. Most microfluidic systems are inherently limited to the low Reynolds number regime, which only results in laminar flow. Mixing of fluid in miniaturized bio-analytical instruments, therefore, is strongly dominated by diffusion effect only. Consequently, microfluidic mixing tends to be slow and requires a long period of time as well as a relatively long distance to obtain complete and homogenous mixing. Our group works on the novel microfluidic mixers that take advantage of field-effect control to dynamically manipulate local flow field to highly enhance mixing effect in microchannel.

Technical Approach:

A novel active electrokinetic microfluidic mixer based on periodical field-effect control to dynamically manipulate local flow field in the microchannel is developed. This mixing mechanism combines temporal modulation (periodical out-of-phase AC radial voltage control) with spatial modulation (asymmetric-herringbone-electrode feature) on the ζ-potential of the microchannel walls to generate complex flow field for mixing enhancement. A theoretical analysis model is developed. A Matlab program is utilized to quantitatively characterize mixing efficiency. Theoretical analyses and numerical simulation have been developed, including the influences of buffer pH, electrolyte concentration, and radial voltage on the ζ-potential, and the flow field analysis with nonuniform ζ-potential. Our work reported at Sensors and Actuators A: Physical 118(1), 31, pp. 107-115, 2005 is considered as the first report taking temporal/spatial ζ-potential modulation for microfluidic mixer applications.

Fig. 1 Illustration of our T-shape micromixer with a 200 um×60 um cross-section.

Fig. 2 Illustration of the electroosmotic flow field in the vicinity of the solid-liquid interface.

Fig. 3 Illustration of an electroosmotic flow through a rectangular channel, which has different ζ-potential on the channel wall in each region.

Fig. 4 CFD-ACE+ simulation results for the transverse velocity vectors and the concentration contours on different cross-sections (y–z planes) along the microchannel: (a), (b), (c), and (d) show the results at the distance of 0.8, 1.6, 2.4, and 3.2mm along the microchannel, respectively.

Fig. 5 Schematic representation of our experimental setup.

Fig. 6 Microscope pictures of the sample solution flowing from up to down: (a) and (b) represent the distribution status for rhodamine dye under zero applied radial voltage and applied alternate 100 V/-50V voltage at odd/even Al electrode, respectively.

Fig. 7 The mixing index at different downstream distance from the T-junction for both no ζ-potential control and ζ-potential control.

Fig. 8 Photograph of an electroosmotic flow with uranine dye flowing from the EOF-suppressing region to the EOF-supporting region.

References:

1. Hsin-Yu Wu and Cheng-Hsien Liu, "A Novel Electrokinetic Micromixer," Sensors and Actuators A: Physical 118(1), 31, pp. 107-115, 2005. ("Research Highlights" section of Lab on a Chip, 2005, 5, 370-373) (Top 1 hottest article shown on the ScienceDirect TOP 25 Hottest Articles quarterly report web site)

2. Hsin-Yu Wu and Cheng-Hsien Liu, "A Novel Electrokinetic Micromixer," Proceedings of Twelfth International Conference on Solid State Sensors and Actuators (Transducers'03), pp. 631-634, 2003.

3. Hsin-Yu Wu and Cheng-Hsien Liu, "A Passive Micromixer for Microfluidic Biochips," Technical Report to ROC National Science Council and DR. Chip Biotechnology Inc., Taiwan, 2003.

Contact Information :

· Hsin-Yu Wu rainingwu@gmail.com

· Cheng-Hsien Liu liuch@pme.nthu.edu.tw