Abstract
Applications of DNA assays have grown rapidly in recent years. Novel technologies are also developed for DNA assays. The high specificity of DNAs is useful for detecting target DNAs reliably. This thesis proposed two methods for detecting the hybridization and amplification of DNAs through biocompatible gold as microelectrodes. As hybridization occurs on the electrode surface, DNAs accumulate on the surface. Therefore, the charges increase and the double-layer capacitance of the electrode-electrolyte interface decreases. To avoid the conventional fluorescent-labeling methods, circuits for detecting either the intrinsic charges of DNAs or the impedance change induced by DNAs are proposed. To detect the intrinsic charges, EGFET integrated with gold electrodes and readout circuits are design to record the signal as an output voltage. In addition, an ultra low-pass filter with noise cancellation is employed to eliminate the high-frequency noise. To detect the change of the double-layer capacitance, an operational amplifier with a feedback capacitor array is connected to a gold electrode. As the double-layer capacitance changes with the DNA binding to the electrode surface. The capacitance change is amplified as an output voltage. Both type of circuits are integrated with gold microelectrode arrays on a single chip. The capability of the chip to detect the hybridization and amplification of DNAs are tested.