In developing fluorescence-based biosensors for rapidly determining metal ions such as zinc or copper in complex media such as sea water, serum, cerebrospinal fluid, or the interior of a cell, several issues must be considered. Among these are the selectivity, sensitivity, ease of calibration, speed of response, reversibility, stability, and the ease of immobilization onto a solid substrate. While the first three have been dealt with in the design of our transducer molecule, apocarbonic anhydrase II, the others remain to be considered. In this paper we examine the stability of the apoprotein to storage at various temperatures and pHs with a view to establishing storage conditions and lifetimes in operating environments for sensor transducers. Similarly, we immobilized a storage conditions and lifetimes in operating environments for sensor transducers. Similarly, we immobilized a fluorescent-labeled apo-CA variant on quartz to determine its sped, sensitivity, and kinetics of response.