On-line continuous monitoring of glucose or lactate by ultraslow microdialysis combined with a flow-through nanoliter biosensor based on poly(m-phenylenediamine) ultra-thin polymer membrane as enzyme electrode

A miniaturised flow-through biosensor with a cell volume of only a few nano liters was developed in our laboratory. The biosensor can be directly coupl ed to a microdialysis or ultrafiltration probe. Sampling and continuous on- line monitoring can thus be carried out at submicroliter levels and as a co nsequence quantitative recoveries of the analyte of interest are achieved. Via this method excessive calibration procedures, as are necessary with con ventional microdialysis, are avoided. Here, the construction and the perfor mance of such a biosensor for the continuous on-line monitoring of glucose and lactate will be presented. The biosensor is based on the amperometric d etection of hydrogen peroxide after conversion of the analyte of interest b y an immobilised oxidoreductase enzyme. Immobilisation of the enzyme is per formed through electropolymerisation of m-phenylenediamine. Strategies to i mprove the performance (e.g. linearity, selectivity and stability) of the m iniaturised biosensor are discussed and ex vivo and in vivo experiments car ried out thus far demonstrate the potential of this miniaturised flow-throu gh biosensor.