| DNA microarrays have become an indispensable research tool among medical researchers, allowing them to investigate relationships among genes, proteins, and drugs in complex systems. Conventional DNA microarray technology uses lasers, optics, and fluorescent labels, resulting in expensive and bulky systems which are ill-suited for point-of-care medical diagnostics. In this thesis, we describe a label-free electrical detection scheme for use in DNA microarray applications which operates by sensing charge in DNA molecules undergoing polymerization. As the polymerization occurs, a transient signal is induced on a nearby electrode which is sensed by an integrating amplifier. The system comprises a microarray chip and readout system combined in the same package.;We present a multi-channel measurement system built with off-the-shelf electronic components for use with an electrode array fabricated in the Stanford Nanofabrication Facility. Moreover, we will discuss the design of a CMOS label-free DNA microarray in a conventional 0.18 micron process. Our design does not require sophisticated post-processing as do other electrical DNA detection schemes because the sensing electrodes are fabricated in the top-metal layer. Furthermore, we discuss design constraints imposed on current or charge sensing microarrays in order to mitigate crosstalk between electrodes. Using our chip, we demonstrate the detection of DNA molecules undergoing polymerization. We show that the limit-of-detection in the presence of a functionalized surface is 25 fC with a measurement time of 1 second. In terms of target concentration, we estimate that the limit-of-detection with our test setup to be 8 ng/mL; however, with optimization that the limit should be reduced by 5 orders of magnitude. |
