Fabrication of screen-printed electrodes with long-term stability for voltammetric and potentiometric applications

Ensuring the long-term stability of screen-printed (SP) reference electrodes (REs) is increasingly essential because a major technical challenge in fabricating electrochemical sensors using screen printing is preparing an RE with a stable potential as it scales down in size. In this study, we fabricated SP electrodes that exhibit long-term stability in voltammetric and potentiometric experiments. The SP electrodes consisted of carbon working electrodes, a carbon counter electrode, an Ag/AgCl RE, and an ion-selective electrode (ISE) for detecting nitrate ions. The Ag/AgCl RE featured an electrolyte layer, a hydrophobic junction layer, and a small hole, collectively contributing to its long-term stability. This design achieved potential stability with minimal drift over extended periods in both 0.01 M PBS (pH 7.4) and 0.1 M Bis-tris (pH 6.5) buffer solutions. Additionally, the SP Ag/AgCl RE exhibited relatively low potential drift in the presence of various chemicals and different pH solutions. We analyzed the electrochemical behavior of two redox species, Fe(CN)₆^3-/4− and Ru(NH₃)₆^2+/3+, using cyclic voltammetry and electrochemical impedance spectroscopy techniques at the SP electrodes. Potentiometric experiments confirmed the sensitivity, long-term stability, and selectivity of the SP ISE for nitrate ion detection, even in the presence of interfering ions.