Microdialysis coupled to online enzymatic assays

In vivo sampling of interstitial fluid by using microdialysis fibers has be come a standard and accepted procedure. This sampling method is generally c oupled to off line analysis of consecutive dialysate samples by high-perfor mance liquid chromatography or capillary electrophore sis, but this combina tion is not the best approach for some applications, especially those which require high temporal resolution and rapid data collection. The purpose of this review is to provide information on enzyme-based online assays, i.e., continuous analysis of the dialysate as it emerges from the outlet of the sampling device. We have focused on methods developed specifically for the analysis of solutions perfused at a very slow flow rate, i.e., a feature of microdialysis and ultrafiltration techniques. These methods include flow e nzyme-fluorescence assays, flow enzyme-amperometric assays, and sequential enzyme-amperometric detection. Each type of assay is discussed in terms of principle, applications. advantages, and limitations. We also comment on im plantable biosensors, an obvious next step forward for in vivo monitoring o f molecules in neuroscience. (C) 2001 Academic Press.