Small-volume on-line sensor for continuous measurement of γ-aminobutyric acid

We report the first on-line electrochemical sensor for the continuous measurement of gamma-aminobutyric acid (GABA), which is a well-known inhibitory neurotransmitter in the nervous system. The sensor is composed of a glutamate oxidase (GluOx) and catalase immobilized small-volume enzymatic reactor and a glassy carbon (GC) electrode modified with a top layer film consisting of gabase and GluOx coimmobilized bovine serum albumin and an Os-poly(vinylpyrridine) bottom layer film containing horseradish peroxidase. The response of the sensor depends on the a-ketoglutarate concentration and is almost saturated when its concentration is 100 times higher than GABA, The sensor exhibits a sensitivity of 1.56 nA/mu M for GABA under optimized conditions and shows almost no response when 10 mu M glutamate is continuously injected. A detection limit of 0.1 mu M is obtained with a linear range of 0.1-10 mu M. GABA can be measured in the absence of alpha-ketoglutarate when there is L-glutamate in the sample solution, which is a typical condition for the extracellular measurement of cultured nerve cells.