Potentiometric Bipolar Batteries for Ion Sensing. 3D Printed Comb Sensors.

We propose a concept leading to pronounced sensitivity increase of potentiometric analysis based on application of potentiometric bipolar batteries. The system is composed of an array of individual cells; each of them is comprising an ion-selective electrode (ISE) and a reference silver/silver chloride electrode. The cells are connected in series in the absence of additional wiring but form closed bipolar electrode systems composed of ISE and the reference electrode of the neighboring cell. Advantageously, the cell arrays are produced by a 3D printing method using biodegradable polylactide filaments. Potentiometric studies were carried out on model examples of potassium ISEs, supplemented by results obtained also for calcium-ISES to compare the role of the analyte ion charge. It was found that the recorded slope of linear dependence of the voltage on logarithm of potassium and calcium ions activity corresponds to the Nernstian value multiplied by the number of cells. The selectivity of the proposed system with potassium-ISE is high and equal to that of a single electrode. This approach was found applicable for real samples within physiological range of potassium ions concentration; moreover, due to enhanced sensitivity, a linear dependence of the voltage directly on potassium ions concentration in physiological range was obtained, with concentration resolution error smaller than 1%.