ANYL 176 |
| An integrated conductivity detector system was developed for the quantitative counting of un-stained cells in a microchip flow cytometer. The detector was constructed with a platinum wire (76 µm diameter) inserted into a poly(methylmethacrylate), PMMA, chip, which was followed by micro-milling to generate a pair of electrodes with an end-to-end spacing of 50 µm. The Pt wire was situated orthogonal to the fluidic channel with the channel height equal to the wire diameter to allow interrogation of the entire effluent. The conductivity detector measured the relative change in solution conductivity between the pair of platinum electrodes as tumor cells traversed through the microchannel. The high sensitivity of this detector for transducing single cells resulted from nullification of the effects of the parasitic capacitance, Cp, produced by the electrical wiring and the double layer capacitance, Cd of the pair of electrodes using a parallel configuration of a synthetic inductor, L (132 mH), and a gyrator circuit. An AC current of ±5 µA was used to drive the sample cell at a target frequency of 40 KHz to minimize the impedance due to Cd and also hold the inductance to a reasonable value. Using this detector, different tumor cell densities were hydro-dynamically driven through the detector at constant flow rates while monitoring the conductivity change from a single cell traveling through the electrode pair. The correlation of the resultant conductivity signal with single tumor cells was confirmed with video microscopy acquired in real time and simultaneously with the conductivity measurement. A calibration plot of different cell densities was constructed and found to be linear within the concentration (slope = 0.994, r = 0.999) and an observed detection efficiency of ~100%. Circulating Tumor Cells (CTCs) were also enumerated following capturing experiment with EpCAM specific antibody. Key words: flow cytometry, microfluidic chip, conductivity-detector, CTCs. |
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General Posters
7:00 PM-9:00 PM, Sunday, August 19, 2007 BCEC -- Exhibit Hall - B2, Poster
Sci-Mix
Division of Analytical Chemistry |