Microfabricated self-referencing pulstrodes

Screen printing and inkjet printing are attractive processes to produce low-cost and mass producible electroanalytical sensors. Despite important advances in the field, obtaining a printed electrochemical reference element that satisfies analytical requirements has not yet been realized satisfactorily. This paper investigates the use of screen printing and inkjet printing to produce a self-contained, all-solid state reference element that can be integrated with a wide range of electroanalytical sensing principles. The principle relies on a silver/silver iodide element that self-generates its potential by the application of a so-called pulstrode protocol. Specifically, a defined quantity of iodide is released by a short cathodic current pulse, and the reference potential defined by the released iodide is subsequently recorded at zero current. Both screen and inkjet-printed reference electrodes are fabricated and characterized, and the methodology optimized and assessed. As an application example, a single-point calibration method is used to quantify ions in undiluted filtered urine samples by potentiometry. The screen-printing approach was less successful owing to the low purity of the silver ink used. The inkjet printing approach allowed one to quantify chloride and sodium in urine. Using a conventional silver/silver chloride reference electrode as standard, relative errors of respectively 7.7 and 14.1% for chloride and sodium were obtained. While the approach would benefit from further optimization for long term applications, especially the use of high purity silver inks, it is a promising strategy for the realization of fully integrated all-solid-state microfabricated sensing systems.