Progress on solution of two general problems regarding the use of in vivo planar microchemical sensors is reported. These are issues of short term and long term response stability. Reduction of preconditioning time (hydration period), i.e., the time needed by the planar microchemical sensors based on Kapton(R) substrate to achieve the optimal analytical performances, has been achieved. By storing the electrodes in containers with humid atmospheres (100% humidity) their short time responses, e.g. measured potential, when placed in samples to be analyzed, are practically constant after one minute of immersion. The electrode sensitivity, potential reproducibility and membrane resistance of both pH and K+ sensors were evaluated and compared before and after placing them in whole blood samples for specified periods of time. Blood serum samples were successfully assayed and the results compared with those obtained with a pH glass electrode and a blood gas analyzer, respectively. The long term stability of the membranes for in vivo use was investigated by determination of cell adhesion and membrane biostability (at 14 days of subcutaneous implantation in rats) using scanning electron microscopy.
