Evaluation of permselective membranes for optimization of intracerebral amperometric glutamate biosensors

Monitoring of extracellular brain glutamate concentrations by intracerebral biosensors is a promising approach to further investigate the role of this important neurotransmitter. However, amperometric biosensors are typically hampered by Faradaic interference caused by the presence of other electroactive species in the brain, such as ascorbic acid, dopamine, and uric acid. Various permselective membranes are often used on biosensors to prevent this. In this study we evaluated the most commonly used membranes, i.e. nafion, polyphenylenediamine, polypyrrole, polyaniline, and polynaphthol using a novel silica-based platinum electrode. First we selected the membranes with the highest sensitivity for hydrogen peroxide in vitro and an optimal selectivity against electrochemical interferents. Then we evaluated the performances of these membranes in a short lasting (3-4h) in vivo experiment. We found that best in vitro performance was accomplished with biosensors that were protected by a poly(m-phenylenediamine) membrane deposited onto the platinum electrode by cyclic voltammetry. However, post-implantation evaluation of these membranes showed poor selectivity against dopamine. Combination with a previously applied nafion layer did not protect the sensors against acute biofouling; indeed it was even counter effective. Finally, we investigated the ability of our biosensors to monitor the effect of glutamate transport blocker DL-TBOA on modulating glutamate concentrations in the prefrontal cortex of anaesthetized rats. The optimized biosensors recorded a rapid 35-fold increase in extracellular glutamate, and are considered suitable for further exploration in vivo.