DIRECT-DETECTION OF THE HYBRIDIZATION OF SYNTHETIC HOMO-OLIGOMER DNA-SEQUENCES BY FIELD-EFFECT

Homo-oligomer DNA strands were immobilized onto silicon/silicon dioxid e electrodes using 3-aminopropyltriethoxysilane. These modified substr ates were used as working electrodes in a three-electrode electrochemi cal cell. In-phase and out-of-phase impedances were measured in the ra nge -1 to +1 V with respect to an Ag/AgCl reference electrode, with a superimposed 10 mV ac signal at frequencies of 20 and 100 kHz. Ex situ hybridization with complementary oligomer strands, performed at the s urface of modified electrodes, is clearly reflected by negative shifts of about 100 mV in the flat-band potential of the semiconductor. Cons ecutive hybridization-denaturation steps show that the shifts are repr oducible and the process is reversible. The in situ hybridization of c omplementary strands has also been observed with impedance measurement s at Si/SiO2 substrates and with the use of a field effect device. The direct detection of hybridization with a field effect device was perf ormed under constant drain current mode, and the corresponding variati ons observed for the gate potential during hybridization are in good a greement with the flat band potential shifts observed with the impedan ce experiments. Measurements made in the presence of noncomplementary strands demonstrate the selectivity of the device.