This paper described a label-free and fully integrated impedimetric biosensor using standard Complementary Metal Oxide Semiconductor (CMOS) technology to measure both capacitance and resistance of the electrode-electrolyte interface. Conventional impedance biosensors usually use bulky and expensive instruments to monitor the impedance change. This paper demonstrate a low power, high gain and low cost impedance readout circuit design for detecting the biomolecular interactions of deoxyribonucleic acid (DNA) strands at the electrode surface. The proposed biosensor circuit is composed of a transimpedance amplifier (TIA) with two quadrature phase mixers and finally integrated with 5 μm x 5 μm microelectrode based on 0.18 μm Silterra CMOS technology process with 1.8 V supply. The output value of the readout circuit is used to estimate the amplitude and phase of the meausred admittance. The developed TIA can achieve a gain of 88.6dB up to frequency of 50MHz. It also has very good linearity up to 2.7mA and the overall dynamic range is approximately 90dB. .
