Postdoctoral Research, 2010-present
For my postdoctoral research in the Allbritton Lab at the University of North Carolina, I have been characterizing a microfluidic device for single-cell enzyme assays and applying this device to measurements of peptidases and kinases in single cells. Show/hide details.
Single-Cell Enzyme Assays. Individual cells, even when they seem the same, can behave vary differently. In fact, this cell-to-cell variation is important in many biological processes, including embryonic development, immunity, and drug resistance. Variation in enzyme activity is an important source of cellular heterogeneity , but single-cell enzyme measurements are challenging because cells are small, complex, and dynamic. In the Allbritton lab, I am using a microfluidic device to steer cells toward a laser pulse for lysis, then separating the cell contents by electrophoresis, and detecting a fluorescent-labeled reporter peptide to measure enzyme activity.
COMSOL Simulations. One of my first projects in the Allbritton lab was to refine a COMSOL model built by former postdoc Dr. Hsuan-Hong Lai and use the model to characterize sample transport on our microfluidic device. Modeling is a powerful tool for microfluidic device design because different geometries and parameters can be tested much more quickly in simulations than in the lab. The COMSOL Multiphysics program uses finite element analysis to solve a system of differential equations that describe the physics of a system. For our model, I modeled the electric fields, pressure-driven flow, diffusion, and electrokinetic forces in the device. The results of these simulations were validated with experiments performed under the same conditions. The results agreed well and suggested that the device design works best for analytes with a high electrophoretic mobility. Undergraduate Jessie Xiong also worked with me on this project and is a co-author on our publication in Electrophoresis .
Experiments (A-D) and simulations (E-G) of sample transport on the device.
Graduate Research, 2004-2009
My graduate research in the Jacobson Lab at Indiana University focused on developing new nanofabrication techniques, understanding the physical phenomena that dominate nanofluidic devices, and applying these devices to trapping and chemotaxis assays of bacterial cells. Show/hide details.
In-plane nanochannels. My first project in graduate school used near-field effects that occur when light interacts with a nanoscale feature to produce three-dimensional features using a single UV exposure . (The most common method of doing this requires multiple exposures or a special gray-scale photomask.) While working on my this project, I became proficient at scanning electron microscopy and electron beam lithography. I used these techniques to make in-plane nanochannels, then used these channel to dispense attoliter volumes. (An attoliter is a trillion times small than a microliter, which is about the size of the smallest drop you can easily see. It’s a million times smaller than a picoliter, which is about the volume of a human cell.) Using this device, I dispensed volumes as small as 42 aL .
Out-of-plane nanopores. After working with in-plane nanochannels, I moved to out-of-plane nanochannels, which are made by sandwiching nanoporous track-etched membranes between two crossed microchannels. These devices have many advantages: the microchannels can bring materials of interest directly to the nanopores; the nanopores create regions of intense local electric fields, which can be used to trap particles and cells ; the surface charge of the nanopores becomes very important, resulting in phenomena like electrokinetic sample concentration  and ion current rectification ; finally, the nanopores limit convective and pressure-driven transport between the channels, permitting diffusion-based dispensing that my collaborators and I used for a chemotaxis assay .
Undergraduate Research, 2001-2004
As an undergraduate at Saint Louis University, I worked with Prof. Dana Spence and Prof. R. Scott Martin to develop microfabricated electrodes for microfluidic tools to study vasodilation. After my junior year, I also participated in an REU at the University of Kentucky with Prof. Michael Jay. Show/hide details.
Biomimics for vasodilation studies. Capillaries and microchannels make excellent mimics for the microvasculature because they can be made to match the dimensions of small blood vessels in our bodies. In the Spence and Martin labs, I helped develop biomimetic devices to study the release of nitric oxide released by bovine pulmonary artery endothelial cells .
Microfabricated electrodes. Along with fluorescence and chemiluminescence, amperometry is an excellent detection method for microfluidic devices because the signal to noise ratio remains high even when sample volume is limited. As part of my undergraduate research, I developed and characterized a method for micromolding carbon ink electrodes for implementation on microfluidic chips . This method allows electrodes of multiple materials to be fabricated on the same device. For example, a carbon working electrode can be used with a palladium decoupler .
Fabrication process for micromolding carbon ink electrodes.
I did this work under the guidance of Profs. Dana Spence and Scott Martin with help from graduate students Nick Torrence and Michelle Li. Read about what the Spence Lab and the Martin Lab are doing now.
Research Experience for Undergraduates. In 2003, I participated in an REU at the University of Kentucky and worked in Prof. Michael Jay’s lab optimizing an aqueous nanoparticle suspension for liquid scintillation counting. Liquid scintillation counting typically uses an organic solvent to dissolve fluors, which release light in the presence of radioactive substances. However, the use of organic solvent-based scintillation fluids produces undesirable mixed waste. In the Jay lab, I helped to develop a scintillation fluid in which the fluor molecules were contained in polystyrene nanoparticles suspended in water, eliminating the organic solvent character of the waste . For this project, I worked under the guidance of Prof. Michael Jay and graduate student Jim Weekley.