Development and comparison of biosensors for in-vivo applications

Electrochemical biosensors have been of increasing interest, especially tho se developed to be directly applied in diagnostic areas, such as neuroscien ce. We have been interested in developing a range of biosensors for monitor ing glucose, lactate, pyruvate, and glutamate in order to study on-line bot h brain function in the laboratory and to monitor brain health in neurointe nsive care. For a biosensor to function effectively in these situations, it has to combine the following characteristics: quick response and high sens itivity, good reproducibility and adequate stability. In this study we comp ared the performance of a number of different amperometric biosensors strat egies. These included ferrocene mediation of immobilised enzymes (system A) , a redox hydrogel based system (system B), and a conducting polymer approa ch using polyaniline (system C). All assays were operated as flow-injection systems with upstream immobilised enzyme beds if necessary. When calibrate d for H2O2 systems A and B reacted quickly enough to give quantitative conv ersion up to 0.2 mM. Above this concentration the response was limited by h orseradish peroxidase enzyme kinetics and eventually enzyme loading. System C showed a restricted H2O2 response. When calibrated for glucose (by use o f immobilised glucose oxidase) system B exhibited the highest sensitivity b ut its analytical range was restricted because the system became limited by H2O2 response. System A had low sensitivity for analyte compared to H2O2 a nd system B, but a greater useful range. Problems of mediator cycling betwe en the immobilised enzymes are discussed. System C gave an excellent linear range but sensitivity was limited by background noise. Stability and repro ducibility of the systems are also described. In conclusion, from this stud y the ferrocene system proved to be overall most useful and has now been us ed in the first dual on-line monitoring of glucose and lactate in patients in neurointensive care.