Self-powered Cascade Bipolar Electrodes with Fluorimetric Readout.

Bipolar electrodes working in a self-powered mode are a basis for development of easy to use electrochemical-optical sensors, these systems are very promising due to their simplicity and no need of external polarization. However, the self-powered mode can be used only in cases when the redox potential difference of reactions occurring at opposite poles of the electrode is sufficiently high. To overcome this limitation we propose development of a system working spontaneously, but involving two bipolar electrodes, forming a cascade system. One of electrodes ('driving' electrode) works in self-powered mode and triggers charge transfer processes in the second ('sensing') bipolar electrode. For the sensing electrode an electrochemical process of an analyte occurs at one pole, accompanied by a complementary process at the second pole, inducing an optical (fluorimetric) analytical signal. This concept was successfully tested on a model system of a sensing bipolar electrode with a platinum electrode participating in oxidation of an analyte, L-ascorbic acid, connected with electrode coated by poly(3-octylthiophene), where reduction of the polymer results in formation of fluorimetrically active neutral form. As the driving system bipolar electrodes with zinc wire as one pole, characterized by a low redox potential, were used.