NOVEL TYPE OF ION-SELECTIVE FLUOROSENSOR BASED ON THE INNER FILTER EFFECT - AN OPTRODE FOR POTASSIUM

An optrode for potassium ion has been designed that exploits the inner filter effect (IFE) of fluorescence. The sensing scheme makes use of neutral ion carriers as described by Simon et al., but transduction is based on the use of two different dyes, viz. an absorber and a fluorescer. The absorber acts as the proton carrier, while the other is a stable and pH-independent fluorophore bound to minute particles contained in the sensor membrane. Fluorescence varies as a result of the varying absorption of the dye which in turn is modulated by the potassium concentration through the IFE. The sensor material is extremely sensitive to potassium to which it fully reversibly responds over the 1 muM to 10 mM concentration range with a useful dynamic range from 1 muM to 1 mM. The sensing approach presented here is generic in that it can be applied to almost any species for which respective carriers are known. Thus, by replacing valinomycin by carriers for ammonium and calcium ion, respective ion sensors are obtained without requiring any changes in the optical system.