Reference Electrode‐Free Nitrate Sensing via Differential Temperature‐Modulated Potentiometry in Printed Symmetric SC‐ISEs

ABSTRACT

Nitrate sensors based on solid‐contact ion‐selective electrodes (SC‐ISEs) are a promising technology for low‐cost, continuous ion sensing. However, implementing stable, printable solid‐state reference electrodes that match the scalability of SC‐ISE remains a key challenge. In this work, we exploit the intrinsic thermo‐electrochemical response of SC‐ISEs to extract concentration from temperature‐induced potential modulations without a defined reference potential. Flexible symmetric, fully printed, nitrate‐selective devices are integrated with a printed heating element to enable controlled asymmetric temperature modulation. Using this approach, we measure nitrate concentration (10 ⁻¹ —10 ² m

) via differential temperature‐modulated potentiometry in fully printed symmetric cell configurations. Nitrate sensitivity characterization shows a log‐linear response (0.51 mV/decade, R ²  = 1.00) with good agreement between results obtained from the symmetric cell and those obtained versus a commercial Ag/AgCl reference electrode. Selectivity to key interfering ions is characterized and analyzed. The approach achieves low drift rates of 0.18 ± 0.39 µV/hour (0.081%/ ± 0.176% concentration /hour) in a symmetric cell configuration and demonstrates reversible sensor response under periodic concentration changes. Finally, the impact of temperature and fluid mixing was assessed to quantify the environmental robustness of the proposed approach.