LabAutomation 2006 - SLAS

MP69
Faisal Shaikh
A&M University, Texas
faisal.shaikh@che.tamu.edu
Where Laboratory Technologies Emerge and Merge
Co-Author
Victor M Ugaz,
Concentration, focusing, and metering of DNA in microfabricated analysis chips using
addressable electrode arrays
Microfabricated systems continue to be developed to perform a variety of DNA analysis assays, however many of these applications
deal with such minute amounts of DNA that it must first be concentrated to a detectable level. We have developed microfluidic devices
incorporating an array of parallel on-chip electrodes to locally increase the concentration of DNA in solution. By applying a low voltage
(1V) to the electrodes in the array, the DNA from the solution is sequentially collected on each subsequent electrode, allowing the
quantity of accumulated DNA to be precisely metered in addition to concentrating and focusing the DNA in the sample. We demonstrate
the application of this technique in electrophoresis microchips to inject a narrow, well-defined DNA plug into an electrophoresis gel,
significantly reducing the degradation in separation resolution due to the size of the injected plug. This scheme is robust over different
buffer environments. The electrode array can also be used to achieve a buffer-exchange, wherein the original sample buffer is replaced
with a buffer of interest for further analysis. In another novel application of the electrode array, a new chip design is envisioned wherein an
unpolymerized gel is flown over the captured DNA plug and subsequently polymerized, the sample being locked in place by an opposing
electrokinetic force. The sample plug is then released for separation in the polymerized gel. This scheme allows a more compact and
versatile microfluidic architecture to be designed whereby multiple sample operations can be performed at a single location on the chip.
MP70
Sushil Shrinivasan
University of Virginia
Charlottesville, Virginia
sushil@virginia.edu
Co-Author(s)
Jerome P. Ferrance, Department of Chemistry, University of Virginia
Pamela M. Norris, Department of Mechanical & Aerospace
Engineering, University of Virginia
James P. Landers
University of Virginia
Portable Laser Induced Fluorescence Detection System and Its Application for DNA
Quantitation using a T-Mixer Microdevice
This work details the design of a miniature, low cost, low power, portable laser induced fluorescence (LIF) detection system. The detection
system consists of a 635nm diode laser, which is collimated and focused using an appropriate lens. The emitted fluorescence is filtered
and detected using a photodiode system, which converts light intensity into a voltage that is recorded and stored on a portable computer.
The detection system was evaluated using a T-Mixer glass micro-device in which the fluorescent dye NileBlue (excitation/emission:
630/650nm) was mixed with ethanol. Because the detection point can be selected anywhere along the channel, the time required
for sufficient mixing in this system at different flow rates and dye concentrations was investigated. Linearly increasing and decreasing
concentrations of the dye were then mixed with ethanol to test the limits of the detection system.
Once fully developed, this detection system and T-mixer microdevice were utilized for DNA quantitation on a microdevice through mixing
of a DNA solution and an intercalating dye. Mixing times in the dye/DNA system were determined and compared to theoretical values
based on the diffusion coefficients for the two components. A calibration curve was generated using increasing concentrations of DNA,
against which the fluorescence from a sample solution could be compared to determine the DNA concentration in an unknown solution.
This application illustrates the utility of the portable LIF detection system for DNA detection, showing the potential for utilization of this
miniaturized detection system in microchip electrophoretic DNA separations.
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