A Microfluidic Programmable Array for Label-free Detection of Biomolecules

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One of the most promising ways to improve clinical diagnostic tools is to use microfluidic Lab-on-a-chip devices. Such devices can provide a dense array of fluidic components and sensors at the micro-scale which drastically reduce the necessary sample volumes and testing time. This dissertation develops a unique electrochemical sensor array in a microfluidic device for high-throughput, label-free detection of both DNA hybridization and protein adsorption experiments.

The device consists of a patterned 3 x 3 grid of electrodes which can be individually addressed and microfluidic channels molded using the elastomer PDMS. The channels are bonded over the patterned electrodes on a silicon or glass substrate. The electrodes are designed to provide a row-column addressing format to reduce the number of contact pads required and to drastically reduce the complexity involved in scaling the device to include larger arrays. The device includes straight channels of 100 micron height which can be manually rotated to provide either horizontal or vertical fluid flow over the patterned sensors. To enhance the design of the arrayed device, a series of microvalves were integrated with the platform. This integrated system requires rounded microfluidic channels of 32 micron height and a second layer of channels which act as pneumatic valves to pinch off selected areas of the microfluidic channel. With the valves, the fluid flow direction can be controlled autonomously without moving the bonded PDMS layer. Changes to the mechanism of detection and diffusion properties of the system were examined after the integration of the microvalve network.

Protein adhesion studies of three different proteins to three functionalized surfaces were performed. The electrochemical characterization data could be used to help identify adhesion properties for surface coatings used in biomedical devices or for passivating sensor surfaces. DNA hybridization experiments were performed and confirmed both arrayed and sensitive detection. Hybridization experiments performed in the valved device demonstrated an altered diffusion regime which directly affected the detection mechanism. On average, successful hybridization yielded a signal increase 8x higher than two separate control experiments. The detection limit of the sensor was calculated to be 8 nM.