Platinized Carbon Fibers as an Electrochemical Substrate to Obtain Minimally Invasive Microelectrode Biosensors for Brain Monitoring
Résumé
Local neurochemical disturbances occurring after brain injury provide important information about the ability of the nervous tissue to recover from the initial insult. Monitoring the chemical composition of the brain interstitial fluid is therefore an important challenge for both pre-clinical and clinical research on brain injury. Microelectrode biosensors are a promising technique to monitor the brain with a temporal resolution in the order of seconds. Here, ultramicroelectrodes based on platinized carbon fibers were fabricated to obtain biosensors with less than 15 µm external diameter. Platinization was achieved by sputtering a 10 nm Cr adhesion layer followed by 100 nm of platinum. Platinized carbon fibers were then encased in a glass micropipette and covered with electropolymerized poly-phenylenediamine for selectivity, and covalently immobilized oxidase enzymes (glucose oxidase, lactate oxidase, D-amino acid oxidase or glutamate oxidase). After implantation in the rat parietal cortex, such biosensors detected (1) a lower basal lactate concentration, (2) a slower diffusion of glucose and D-serine through the blood brain barrier, and (3) a smaller lactate response to cortical spreading depolarization. The concentrations estimated by the small biosensors based on platinized carbon fibers, and their dynamic changes across time, were significantly different from the estimates provided by more conventional biosensors with 100 µm external diameter. We conclude that such biosensors avoid major mechanical injury to blood vessels, preserve the blood brain barrier at the site of implantation, and therefore, provide more accurate measurements from the brain interstitial fluid