On-chip Microelectrode Capacitance Measurement for Biosensing Applications

Charge-based capacitance measurement (CBCM) is used to implement an on-chip microelectrode biosensor combined with complementary metal oxide semiconductor (CMOS) circuitry. Electrical double-layer capacitance is exploited to measure the interfacial property changes during biorecognition events at electrode surfaces. A test chip with 4 x 4 mu m(2) planar electrodes and a differential capacitance-to-voltage conversion circuit was designed and fabricated using 1.2 mu m CMOS technology. The chip was experimentally characterized in sodium chloride (NaCl) aqueous solutions to demonstrate its feasibility to detect capacitance variation when the ionic concentration is varied between 0.1 mM and 1 M over a wide frequency range. To show the feasibility of the microfabricated electrode for detecting biomaterials in such a small sensor area, the hybridization of 20-mer probe oligonucleotides in a phosphate-buffered solution was demonstrated. A 20% change in capacitance (10 fF) before and after the injection of complimentary target oligonucleotides is successfully observed, showing promise for future miniature yet high-throughput biosensor arrays. (C) 2010 The Japan Society of Applied Physics