Ion-Selective Organic Electrochemical Junction Transistors Based on Poly(3,4-ethylenedioxythiophene) Doped with Poly(styrene sulfonate)

摘要

Ion-selective organic electrochemical junction transistors (IS-OEJTs) were prepared and their performance was studied for the detection of potassium, calcium, and silver ions. In this kind of sensors the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrene sulfonate) (PSS), PEDOT:PSS, is utilized for transduction of chemical information to electronic information in the solid state. In order to achieve selectivity, the channel region of the transistors was coated with ionophore-based polymeric membranes. The organic electrochemical junction transistors (OEJTs) studied in this work differ from the field-effect transistors in the fact that the change in drain/source current is not induced by an electric field but rather by electrochemical reduction/oxidation (undoping/doping) of the conducting polymer in the channel region between the drain and source. Therefore the transistors studied in this work are called electrochemical junction transistors and not field-effect transistors. They are rather regarded as bipolar junction transistors where the source, drain, and gate terms are replaced with emitter, collector, and base, respectively. K+-, Ca2+-, and Ag+-selective OEJTs were characterized by measuring the collector/emitter current (l(c)) as a function of time at constant collector/emitter voltage (V-c) both in absence and presence of applied base voltage (V-B). K+-selective OEJT responds to K+ in the concentration range 10(-1) M-10(-4) M with 0.1. M NaCl as the background electrolyte. Prolonged conditioning of the K+-selective OEJTs in KCl solution caused deterioration in the selectivity of the transistors. The selectivity, however, was regained after keeping the transistors dry for a certain time. In the case of Ca2+-selective OEJTs, various membrane compositions and measuring parameters were studied and compared. Factors such as the base voltage and the concentration of the ionophore and the lipophilic salt in the ion-selective membrane (ISM) influenced the performance of the Ca2+-selective OEJTs. The best selectivity for Ca2+ in the concentration range 10(-1) M-10(-4) M (with 0.1 M K+ as the interfering ion) was achieved by using ca.10 wt% ionophore and 5 wt% lipophilic salt. Ag+-selective OEJTs, both in presence and absence of ISM, gave more complicated response than Ca2+- or K+- selective OEJTs. One reason is that Ag+ is an electroactive ion that may oxidize the PEDOT: PSS transducer layer even in the absence of the base voltage.