Development of a Novel Micro Biosensor for Monitoring Glutamate Release in the Brain

L-glutamate is a prevalent excitatory neurotransmitter in the central nervous system with important roles in a variety of normal neuronal function and also neurological and neurodegenerative diseases (Meldrum, 2000; Hamdan and Zain, 2014; Salazar et al., 2016). While many methods have been employed to detect glutamate levels in the brain, amperometric measurement with a glutamate oxidase-based biosensor offers numerous advantages including high spatial resolution and real-time measurement (Lee et al., 2007; Batra et al., 2016). However, commercially available glutamate biosensor models are expensive and unnecessarily large (Pinnacle Technology, Inc.). In this study, we characterized the performance of a novel, amperometric, glutamate oxidase-based micro biosensor with a 50 μm platinum electrode and an o-phenylenediamine (o-PD) coating. An in vitro calibration curve was created, the linear range was found to reach 150 μM, and the sensitivity to glutamate within this range was 0.0966 nA/μM. The limit of detection was 0.044 μM. Selectivity testing with serotonin, adenosine, dopamine, glucose, uric acid, and ascorbic acid showed no biosensor response to these compounds. Shelf life stability was established but a 55% decrease in sensitivity was measured over a 7-day period. Stimulated glutamate was measured successfully in the subthalamic nucleus of rat brain slices and in vivo. Higher stimulation pulse rates elicited increased glutamate release. In vitro post-calibration of the biosensor after use in brain tissue showed a 47% decrease in sensitivity to glutamate. This miniaturized glutamate biosensor shows promise for further studies in vivo and in disease states such as cerebral ischemia.