Fiber optic biosensor for Co(II) and Cu(II) based on fluorescence energy transfer with an enzyme transducer

We have demonstrated that fluorescence energy transfer may be made the basis of a zinc biosensor employing carbonic anhydrase as the recognition element, or transducer. Herein we describe the use of carbonic anhydrase in a biosensor for Cu2+, and Co2+ using a different transduction scheme. In particular, we have exploited the well-known d-d absorbance bands exhibited by these ions when bound in the active site as energy transfer accepters for suitable fluorescent donors. Binding of the metal ion to the apoprotein results in fluorescence quenching and concomitant reduction of the lifetime, which can be related to fractional occupancy of the binding site and thus concentration of the metal ion.