Microdialysis is an in vivo bioanalytical sampling technique for monitoring local chemistry in the extracellular fluid of an organ and in body fluids. The sampling principle is quite simple: Molecules diffuse from the body compartment through a semipermeable membrane of the sampling cannula into the perfusion medium flowing inside the probe (Delgado et al., 1972; Ungerstedt and Pycock, 1974). The driving force for this molecular movement is passive diffusion down the concentration gradient between the two compartments. Thus, the technique works in both directions: for recovering substances from a living body, and for delivering substances into this organism.
In practice, a microdialysis probe is implanted into the tissue with tubing connecting it to external components: a perfusion pump and a fraction collector. The probe is perfused continually at low flow rate (0.1-10 juL/min) with an artificial physiological solution. As the perfusate emerges from the probe, fractions are collected and samples of each fraction analyzed.
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