Quantitative fluorescence-based biosensing and imaging of zinc and copper in complex media

Summary form only given. In order to be to be useful in complex media such as serum, cerebrospinal fluid, sea water, and the like, the sensor transducer must be very selective for the analyte of interest, and insensitive to potential interferers. In our case we sought to determine Zn(II) and Cu(II) at trace (nanomolar to subpicomolar) levels in sea water and cerebrospinal fluid, which both contain potential interferers such as Ca(II) and Mg(II) at million-fold higher levels. Thus, we focused on developing a very selective transducer molecule based on a biological molecule, so that the resulting sensor could be termed a biosensor. The biological molecule chosen was a metalloenzyme found in the blood of humans called carbonic anhydrase II, which exhibits extraordinary specificity and avidity for which metal ions it will bind in its active site. In particular, Zn(II) binds with 4 pM affinity and Cu(II) with 0.1 pM affinity, whereas Ca(II) at 10 mM and Mg(II) at 50 mM show no measurable binding at all.