In vivo characterisation of a catalase-based biosensor for real-time electrochemical monitoring of brain hydrogen peroxide in freely-moving animals

Abstract

A catalase-based microelectrochemical biosensor developed for real-time neurochemical monitoring of hydrogen peroxide (H₂O₂) was characterised in freely-moving rats. The in situ sensitivity of the sensor was assessed by the direct delivery of H₂O₂ to the local environment of the implanted sensor and by the chemical manipulation of the endogenous concentration of H₂O₂. Inhibitors of H₂O₂ enzymatic degradation were utilised including sodium azide (SA) and mercaptosuccinate (MCS). SA and MCS primarily inhibit catalase and glutathione peroxidase (GPx) respectively and the application of each resulted in a significant increase in the H₂O₂ signal. The selectivity of the sensor was verified by the absence of a change in the signal in response to the peripheral administration of ascorbic acid (AA) compared to controls. Evidence of a disparity between brain H₂O₂ signalling in the freely-moving animal with respect to the anaesthetised subject was also observed. The enzymatic component of the paired H₂O₂ sensor was found to be stable over a continuous monitoring period of 12 days, thereby demonstrating the suitability of this sensor for the long-term chronic detection of brain H₂O₂.