Aqueous buffer protection system for biosensors

Usable life of a biosensor life is extended while keeping the sensing system enclosed and minimizing the introduction of flushing solutions into a measurement line (e.g., a blood vessel) of a fluid system, such as a human blood vessel, a nutritional fluid line in a tissue cultivation system, or a circulation system in an organ preservation system. A catheter, tube, or other lumen contains the active biosensor. One end of the lumen is introduced to the target fluid, and the other end is connected to a supply of a buffer solution (e.g., heparinized saline solution). By advancing the buffer solution along the lumen, the biological fluid (e.g., blood) can be purged from the area around the sensor material to halt any reactions. When a measurement is desired, then the buffer solution is withdrawn (e.g., suctioned) back into the supply so that the biological fluid enters and contacts the sensor material.