Microfabricated On-Line Sensor for Continuous Monitoring of L -Glutamate

An on-line sensor was developed by using a micro-machining technique for the continuous measurement of extracellular glutamate. The sensor was made by bonding two glass plates together. One of the plates has a rectangular flow channel which is connected to both a sampling and an outlet capillary. The other has a carbon film-based electrochemical cell, which consists of an enzyme-modified electrode surrounded by polymer film to form a thin-layer-channel flow cell. The sensor has a high analyte conversion efficiency due to the cell structure. As a result, we obtained a low detection limit of 44 nM (S/N=3). The cathodic current started to increase about 10 s after sample introduction at a flow rate of 2 μl/min due to its small inner volume. Using the sensor, we can monitor the extracellular L -glutamate increase caused by stimulating it with KCl and γ-aminobutyric acid (GABA) by locating the sampling capillary very close to the cell.