Analytical Sciences

Development of a Surface-Reaction System in a Nanoliter Droplet Made by an Ink-jet Microchip

Yuki KUDO,* Takako NAKAHARA,* Tatsuro NAKAGAMA,* Nobuko SEINO,** Masaki SHINODA,** and Katsumi UCHIYAMA*

*Faculty of Urban Environmental Sciences, Tokyo Metropolitan University, 1-1 Minamiohsawa, Hachioji, Tokyo 192-0397, Japan
**Fine Technology Components Department, Tokyo Factory, Fuji Electric Systems Co., Ltd., 1 Fuji-machi, Hino, Tokyo 191-8502, Japan

A surface-reaction system in a nanoliter water pool using an ink-jet microchip was developed. The reaction system in the nanodroplets formed on a poly(dimethylsiloxane) (PDMS) coated glass slide increased the diffusion-controlled reaction without using a nano-pump, specialized connector or highly sensitive detector. When nanoliter droplets were placed on the PDMS surface with a distance of 100 µm between them by the ink-jet microchip, the repeatabilities of the fluorescence intensity were 2.9% RSD (n = 7). The used ink-jet microchip had 4 different injection ports, and the distance between the ports was 0.995 mm. It was necessary to correct the distance in order to mix or dilute samples in a small droplet. The correction was successfully performed by moving the X-Y stage using inhouse-made software. A linear relationship was obtained between the Resorufin concentrations and the fluorescence intensity. We applied this system to an enzyme-linked immunosorbent assay (ELISA) for immunoglobulin A (IgA), and observed a difference in the fluorescence intensity derived from the amount of IgA (blank, 6.25 ng/mL, 12.5 ng/mL). These results show the usefulness of the open-type micro-analytical systems proposed by us.

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