Analytical Sciences

Enzyme Immunoassay Using a Reusable Extended-gate Field-Effect-Transistor Sensor with a Ferrocenylalkanethiol-modified Gold Electrode

Masao KAMAHORI,* Yu ISHIGE,* and Maki SHIMODA**

*Central Research Laboratory, Hitachi, Ltd., 1-280 Higashi-Koigakubo, Kokubunji, Tokyo 185-8601, Japan
**Hitachi ULSI Systems Co., Ltd., 1-280 Higashi-Koigakubo, Kokubunji, Tokyo 185-8601, Japan

A reusable extended-gate field-effect transistor (FET) sensor with an 11-ferrocenyl-1-undecanethiol (11-FUT) modified gold electrode was developed for applying to enzyme immunoassay. It was found that the 11-FUT modified FET sensor detected a thiol compound 50 times or more repeatedly after a treatment with a 5% hydrogen peroxide solution. The gate-voltage shift of the FET sensor showed a fairly good linearity (R² = 0.998) within a range from 10^-2 to 10^-6 M on the concentration of 6-hydroxyl-1-hexanethiol, which is a thiol compound, at a Nernstian response of 58.5 mV/decade. The FET-based immunoassay was constructed by combining the 11-FUT modified-FET sensor with the enzyme-linked immunosorbent assay (ELISA), in which the enzyme chemistry of acetylcholinesterase (AChE) was used to generate a thiol compound. The 11-FUT modified FET sensor with an AC voltage at 1 MHz superimposed onto the reference electrode detected the AChE-catalyzed product corresponding to a serum concentration of interleukin 1β from 10 to 5000 pg/mL. In addition, all measurements were successfully performed by using the same FET-sensor chip after a treatment with a 5% hydrogen peroxide solution.

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