Fluorimetric readout of ion-selective electrode potential changes

A novel method of quantitative optical readout of potentiometric responses of ion-selective electrodes is proposed. This idea was realized in a simple self-powered bipolar electrode system, with an ion-selective pole directly connected with the second pole, where a fluorimetric signal is generated. In this way, space and time separated optical readout and sampling can be achieved. This concept was tested on a model example of a system containing potassium-selective electrode (ISE-K) with polypyrrole solid contact, connected to a zinc wire immersed in the solution. In this arrangement increase of potassium ions activity in the solution results in change of the membrane potential of ISE-K, inducing reduction of polypyrrole solid contact and corresponding oxidation of the other omponent - zinc. Increase of zinc ions concentration is read as increase of emission intensity. Thus, this simple system allows quantitative in situ potassium ions determination, with the fluorescence intensity being a linear function of logarithm of analyte activity in solution in turn-on mode. Moreover, due to simplicity of the system and presence of reactants in the solution phase, a quantitative correlation between electrochemical and optical behaviour was confirmed and indications for the system optimization could be proposed.