Analytical Sciences

Bifunctional Tri(ethylene glycol) Alkanethiol Monolayer Modified Gold Electrode for On-Chip Electrochemical Immunoassay of pg Level Leptin

Tetsuya NISHIMURA,*,** Yukari SATO,* Mutsuo TANAKA,* Ryoji KURITA,* Kohei NAKAMOTO,*,** and Osamu NIWA*,**

*National Institute of Advanced Industrial Science and Technology (AIST), Central 6, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan
**Graduate School of Pure and Applied Science, University of Tsukuba, 1-1-1 Tenno-dai, Tsukuba 305-8573, Japan

An on-chip enzyme-linked immunosorbent assay combined with an electrochemical detection method (EC-ELISA) was employed to detect a leptin, one of the most important adipose derived hormones, using gold electrodes modified with a tri(ethylene glycol) terminated short alkanethiol (TEGCnSH, Cn = (CH₂)n, n = 2, 4, 6, and 8) monolayer. These TEGCnSH monolayers on gold electrodes can suppress non-specific protein adsorption without affecting the electrochemical activity required for detecting p-aminophenol (PAP), which is an alkaline phosphatase (ALP) product. We measured leptin with a highly sensitive detection range (100 pg mL⁻¹ to 10 ng mL⁻¹ level) and with the desired detection limit (13.6 pg mL⁻¹) by using electrochemical detection. For detecting leptin, the EC-ELISA method using TEGC4SH modified gold electrode with a poly(dimethylsiloxane) based microchannel was superior to the conventional ELISA method. With the EC-ELISA method, we were able to measure leptin with a satisfactory detection range and a pg level detection limit within 30 min, which is a much lower detection level than that obtained with conventional plate based ELISA.

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