Potential behavior of biochemically modified gold electrode for extended-gate field-effect transistor

We propose potentiometric detection of biomolecules using an extended-gate field-effect transistor (EGFET). Using a gold film electrode as the extended gate, the stability of the interface potential was characterized for a shift and a drift, and found to depend on the surface roughness of the gold electrode. The surface of the gold film was coated with self-assembled monolayers (SAMs) of various types of alkanethiol molecules with functional sites such as amino groups, carboxyl groups, hydroxyl groups and oligonucleotides. In all the alkanethiol molecules, the interface potential decreased drastically just after the introduction of each molecule because of the negative charges of thiol groups in aqueous solutions. Moreover, the complementary target deoxyribonucleic acid (DNA) has been introduced to the gold electrode modified with oligonucleotide probes and hybridized with them. The interface potential shifted in the negative direction due to the negative charges of the target DNA. Thus, the charge density change due to DNA hybridization as well as the adsorption of alkanethiol molecules on the gold electrode could be successfully detected using the biochemically modified EGFET.