Electrochemical quartz crystal microbalance (EQCM), which is capable of sensitive measurement for mass and electrochemical signals, was employed to analyze specific-sequence DNA. Self- assembled monolayers with carboxy groups were first coated on the gold electrode of a quartz crystal resonator by adsorption of α- thioctic acid, ssDNA of 20-mer oligonucleotides was then covalently attached to the surface via N-ethyl-N'-(3-(dimethyl) aminopropyl) carbodiimide hydrochloride (EDC), N-hydroxysuccinimide (NHS) as probe molecules. The processes for self-assembly of α-thioctic acid, immobilization of the probe and hybridization of the target DNA were real-time characterized, and the amounts of immobilized ssDNA and hybridized cDNA in acidic, basic and neutral solution were determined. It is found that both of the amounts of immobilized ssDNA and hybridized cDNA are depended on solution pH, and this phenomenon is explained reasonably in this paper. After hybridization, the gold electrode of the quartz crystal resonator was reacted with Hoechst 33258, which is a DNA minor grove binder and can bind to dsDNA hybrids. Electrochemical signals of Hoechst 33258 were measured to characterize the processes of DNA hybridization. Qualitative and quantitative analysis of specific sequence of DNA can be performed in this way without a label.

Key words: ELECTROCHEMISTRY, QUARTZ, CRYSTALS, HYBRIDIZATION