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Research

Research Thrusts

  • Microfabrication/Microfluidics: Designing and fabrication of novel microfluidic devices. Material processing include silicon, glass, and polymer-based devices including PDMS (soft-lithography).

  • Digital microfluidics: The generation and translation of micro-liter droplets utilizing capillary forces, surface tension, electrowetting, and thermal effects

  • Electrokinetics: The investigation of electric-field induced forces for the manipulation of particles and generation of hydrodynamic forces. Phenomena include dielectrophoresis, electrophoresis, electro-osmosis (AC & DC), electrothermal hydrodynamics, electro-rotation, electro-orientation, electrokinetic self-assembly, and colloid polarization.

  • Thermal-hydrodynamics: Fluid and device heating at this scale generally occurs through Joule heating (a.k.a. ohmic heating) or an external heating source, such as a focused laser beam. This can lead to sharp thermal gradients and generate electrothermal fluid motion, thermophoresis, or Marangoni surface effects. Our research focuses on utilizing these thermally-induced phenomena for efficient fluid pumping and/or particle separation.

  • Optics: Investigations include (i) optical trapping of particles, (ii) optically-induced thermal forces, (iii) opto-mechanical actuation of carbon-nanotubes, and (iv) optically-induced electrokinetic mechanisms utilizing photoconductive materials.

  • Biological characterization: Additional research focus is aimed at the utilization of the above techniques for the capture, sorting, and characterization of biological entities. Specific thrusts include impedance-based characterization of cell layers, dielectrophoretic selective trapping of particles, and microfluidic pumping of biological media.

Ongoing Research Projects

  • Rapid Electrokinetic Patterning (REP): a novel optically controlled electrokinetic method that can rapidly concentrate, pattern, and sort colloids from 50 nanometers to 3.0 micrometers. This phenomena is governed by the behavior of the particle's electric double layer. A movie illustrating its capabilities is available here.

REP

Illustration of Rapid Electrokinetic Patterning (REP).
From Journal of Micromechanics and Microengineering Vol. 20, 015022 (2010).

  • Dielectrophoresis: This technique refers to the ability to trap, concentrate, sort, and manipulate neutrally-charged particles using AC electric fields. Below illustrates its application with interdigitated electrodes and how polystyrene particles behave differently at different applied frequencies. This technique has been utilized to sort particles of different sizes or sort cells of different type (live cells vs dead cells). Alternatively you can dynamically translate and manipulate single particles, as illustrated in this movie (mpg) showing the oscillatory motion of a 10 micrometer particle.

    DEP

    Dielectrophoretic manipulation of 3.0 micron particles with 20 micron interdigitated electrodes.

  • Optically Induced Microfluidic Pumping: this project involves the optically-induced mechanical actuation of carbon nanotubes (CNT) to generate illumination-driven mechanical microfluidic pumps. This technique involves simple fabrication steps using a biocompatible polymer (PDMS) and is scalable to use in microchannels with sub 10 micrometer dimensions.

    CNT pump
    (left) Illustration of CNT pump design and operation. (right) Experimental images showing water displacement after one pump cycle.
  • Impedance Analysis of Endothelial Cells: A microchannel chip containing electrodes has been designed and tested for the analysis of endothelial cells using impedance characterization. This chip will enable future research towards drug discovery and wound healing for the prevention of heart disease.

    Circuit - Cell   Impedance Chip

    (left) Illustration of equivalent circuit analysis. (right) Fabricated chip, complete with microchannels.


Available Equipment/Processes

  • Particle Image Velocimetry (PIV): A low-noise system capable of acquiring images at 500 ns intervals. Custom computer algorithms correlate the images to obtain a picture of the flow field.

  • Optical trapping (a.k.a. optical tweezers, laser tweezers): A near-infrared  system coupled with a scanning mirror system capable of trapping and positioning a microparticle with micrometer resolution.

  • Electrohydrodynamics: Equipment is in place for a variety of electrokinetic investigations including electrophoresis, electro-osmosis (AC & DC), dielectrophoresis, and traveling wave electrokinetics.

  • Infrared microscope: This enables real-time acquisition of thermal images, gaining insight into a 2D temperature field of the chip and fluid. For additional investigations temperature-dependent fluorescent dye experimentation is available.

 

University of Louisville Collaborators

  • Dr. Robert Keynton (BE) - Dr. Keynton's webpage

  • Dr. Robert Cohn (ECE) - Dr. Cohn's webpage

  • Dr. Balaji Panchapakesan (ME)

  • Dr. Palaniappan Sethu (BE)

  • Dr. Cindy Harnett (ECE)

  • Dr. Keith Sharp (ME)

  • Dr. Kevin M. Walsh (ECE)

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