As a promising platform for micrototal analysis systems and Labs-on-a-Chip, microfludic devices based on the handling of liquid plugs are beginning to attract attention. However, in carrying out chemical detection with a plug of the nL order, sensitive detection of an analyte is an issue, which motivated us to start this study. Electrochemical sensors facilitate miniaturization and integration.

　We developed the device which can detect 30-400 nL of liquid plug(Fig.1). The device consisted of PDMS microflow channels and a thin-film three-electrode system. The flow channel structure consisted of a main flow channel and a handling flow channel with chained rhombuses. The latter was used to measure the volume of plugs. We also used this device for the determination of L-glutamate. Plugs containing L-glutamate and L-glutamate oxidase were prepared and mixed well. Then, the merged plug was mobilized to the electrodes and measured (Fig. 2(a)). Fig. 2(b) shows dependence of the charge on the concentration of L-glutamate. A good linearity was obtained.

Fig. 1 Structure of device

Fig. 2 (a)Procedure of L-glutamate detection. (b) Dependence of charge on L-glutamate concentration.