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. I did this work with Prof. Stephen Jacobson, Kaimeng Zhou, the Brun Lab, and many others.

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 [1]. (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 [2].

A 3D feature produced by one UV exposure.

Attoliter-scale dispensing by modified pinched injection on a nanocross chip.

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 [3]; the surface charge of the nanopores becomes very important, resulting in phenomena like electrokinetic sample concentration [4] and ion current rectification [5]; 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 [6].

Simulation of the electric field gradient at the tip of a conical nanopore.

A confocal fluorescence image of red fluorescent microparticles in a vertical channel trapped at nanopores above a horizontal channel filled with green fluorescent dye (gray).

The paths of individual bacteria (colored lines) as they pass over a nanoporous membrane covering a horizontal channel containing xylose.

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