Simultaneous in vivo monitoring of glucose, ?-lactate, and pyruvate concentrations in rat brain by a flow-injection biosensor system with an on-line microdialysis sampling

A flow-injection biosensor system with an on-line microdialysis sampling is proposed for the simultaneous monitoring of glucose, l-lactate, and pyruvate in rat brain. In the first stage of the operation, the dialysate from the microdialysis probe is delivered to a sample loop of the six-way autoinjector by perfusing Ringer’s solution for 120s at 2μlmin−1. In the second stage, the dialysate collected in the sample loop is automatically injected for 10s into the flow-injection line with a triple enzyme electrode arranged in perpendicular for the flow direction. The triple enzyme electrode is constructed by hybridizing a poly(1,2-diaminobenzene) film to three sensing parts which respond selectively to glucose, l-lactate, and pyruvate, respectively, without any cross-reactivity. The three sensing parts of the triple enzyme electrode respond linearly to the concentrations of glucose, l-lactate, and pyruvate between 0.1 and 10mM, without any interference from oxidizable species present in the dialysate. The proposed flow-injection analysis method can be successfully applied to the simultaneous in vitro and in vivo assays of three analytes in serum and in rat brain, respectively. The system can be automatically processed at an analytical speed of 28dialysatesh−1.