Ph.D. Dissertation Defense by Sangkyung Kim
Friday, August 20, 2004

(Dr. Peter J. Hesketh, Chair)

"Redox recycling for an in-situ enzyme labeled immunoassay on IDA electrodes"


This research is directed towards developing a more sensitive and rapid electrochemical sensor for enzyme labeled immunoassays by coupling redox cycling at interdigitated electrode arrays (IDA) with the enzyme label ?-galactosidase. Coplanar and comb IDA electrodes with a 2.4 ?m gap were fabricated and their redox cycling currents were measured. ANSYS was used to model steady state currents for electrodes with different geometries. Comb IDA electrodes enhanced the signal about 3 times more than the coplanar IDAs, which agreed with the results of the simulation. Magnetic microbead-based enzyme assay, as a typical example of biochemical detection, was done using the comb and coplanar IDAs. The enzymes could be placed close to the sensing electrodes (~10 ?m for the comb IDAs) and detection took less than 1 min with a limit of detection of 70 amole of ß-galactosidase. We conclude that faster and more sensitive assays can be achieved with the comb IDA. A paramagnetic bead assay has also been demonstrated for detection of bacteriophage MS2, used as a simulant for biothreat viruses, such as small pox. The immunoassay was carried out in a microfluidic format with the IDA, reference and counter electrodes integrated on the same chip. Detection of 90 ng/mL MS2 or 1.5x1010 MS2 particles/mL was demonstrated.