Real-Time Amperometric Recording of Extracellular H(2)O(2) in the Brain of Immunocompromised Mice: An In Vitro, Ex Vivo and In Vivo Characterisation Study

We detail an extensive characterisation study on a previously described dual amperometric H(2)O(2) biosensor consisting of H(2)O(2) detection (blank) and degradation (catalase) electrodes. In vitro investigations demonstrated excellent H(2)O(2) sensitivity and selectivity against the interferent, ascorbic acid. Ex vivo studies were performed to mimic physiological conditions prior to in vivo deployment. Exposure to brain tissue homogenate identified reliable sensitivity and selectivity recordings up to seven days for both blank and catalase electrodes. Furthermore, there was no compromise in pre- and post-implanted catalase electrode sensitivity in ex vivo mouse brain. In vivo investigations performed in anaesthetised mice confirmed the ability of the H(2)O(2) biosensor to detect increases in amperometric current following locally perfused/infused H(2)O(2) and antioxidant inhibitors mercaptosuccinic acid and sodium azide. Subsequent recordings in freely moving mice identified negligible effects of control saline and sodium ascorbate interference injections on amperometric H(2)O(2) current. Furthermore, the stability of the amperometric current was confirmed over a five-day period and analysis of 24-h signal recordings identified the absence of diurnal variations in amperometric current. Collectively, these findings confirm the biosensor current responds in vivo to increasing exogenous and endogenous H(2)O(2) and tentatively supports measurement of H(2)O(2) dynamics in freely moving NOD SCID mice.