Minimally invasive microelectrode biosensors reveal different neurochemical signature of spreading depolarization in rat cortex.
Résumé
Monitoring the chemical composition of the brain interstitial fluid is an important challenge for both pre-clinical and clinical research on brain injury. Microelectrode biosensors are a promising technique with a temporal resolution in the order of seconds. Here, ultra-microelectrodes 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 a smaller basal lactate concentration and a slower diffusion of glucose and D-serine through the blood brain barrier compared to more conventional biosensors with 100 µm external diameter. Interestingly, spreading depolarization (SD) produced a smaller increase in lactate, a larger decrease in glucose, and a larger increase in D-serine at platinized carbon fibers microelectrode biosensors compared to larger sensors. Therefore, the neurochemical signature of SDs was significantly different when estimated with these new minimally invasive biosensors. Such small devices 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. Developing smaller, less invasive probes for brain monitoring is therefore an important challenge in order to obtain meaningful information about the cellular mechanisms at work during brain injury.