Nanogap capacitors for label free DNA analysis

Nanogap capacitors are fabricated for DNA hybridization detection. Without labeling, the nanogap capacitors on a chip can function as DNA microarray sensors. The difference in dielectric properties between single-stranded DNA and double-stranded DNA permits use of capacitance measurements to detect hybridization. To obtain high detection sensitivity, a 50 nm gap capacitor was fabricated using a Si-nanotechnology. To ensure proper measurement of DNA's dielectrical properties, the probe ssDNA was first immobilized onto the electrode surface using self-assembly monolayers and allowed to hybridize with the target ssDNA. The capacitance changes were measured for 35-mer homonucleotides. The self-assembly monolayer and DNA immobilization events were verified independently by contact angle measurement and FTIR. Capacitance values are measured at frequencies ranging from 75 kHz to 5 MHz, using 0 V_DC bias and 25 mV_AC signals. Approximately 9% change in capacitance was observed after DNA hybridization at 75 kHz.