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Multiplexed solid‐contact ion‐selective electrodes (SCISEs) are fabricated using printed circuit board (PCB) and mesoporous carbon black (MCB) as ion‐to‐electron transducer (solid contact). Four sensor configurations were examined and showed that in addition to MCB, the sensor configuration plays crucial role in the stability of the potential response. The enhanced sensor stability was also linked with suppression of transmembrane flux of water. The sensors exhibited near‐Nernstian sensitivity (58.1 mV/dec for K+ ISEs and −55.1 mV/dec for NO3‐ ISEs), low detection limits (1.5–2.2 μM), and good short‐term stability (∼0.1 mV/min). Sensors can be stored dry and used without preconditioning. This work demonstrates a promising approach to combining PCB technology and carbon black for large‐scale production of low cost ISEs for point‐of‐care testing, wearables, or in situ field measurements. [ABSTRACT FROM AUTHOR]

We built an integrated solid-contact ion-selective electrode (SCISE) system with the functionality of self-calibration. A multiplexed SCISE sensor (K+ and NO3− vs. Ag/AgCl) was fabricated on printed-circuit board (PCB) substrates and was subsequently embedded into a microfluidic flow cell for self-calibration and flow-through analysis. A PCB circuit that includes modules for both sensor readout and fluid control was developed. The sensors showed a fast and near-Nernstian response (56.6 for the K+ electrode and −57.4 mV/dec for the NO3− electrode) and maintained their performance for at least three weeks. The sensors also showed a highly reproducible response in an automated two-point calibration, demonstrating the potential for in situ monitoring. Lastly, the sensor system was successfully applied to measure mineral nutrients in plant sap samples. [ABSTRACT FROM AUTHOR]

Herein, we demonstrated miniature solid‐contact ion‐selective electrodes (ISEs) using a commercial mesoporous carbon black (MCB) as ion‐to‐electron transducer. MCB is attractive in its high surface area, good conductivity, relative low cost and availability. ISEs for potassium (K+) and nitrate (NO3−) ions were prepared by subsequently coating the sealed glass capillaries (1.5 mm) with MCB and ion‐selective membranes. Addition of MCB substantially stabilized electrode response by providing adequate double‐layer capacitance and lowering resistance by more than 100× compared to the coated‐wire electrodes. The electrodes exhibited near‐Nernstian slopes of 59.6 (K+ ionophore), 57.8 (K+ ion‐exchanger) and −54.8 (NO3− ion‐exchanger) with standard solutions in the range of 10−5 to 10−1 M. Fast response (∼10 s) and reproducible sensitivities were also obtained in a mixed electrolyte containing interfering ions, although with a baseline drift of 2–10 mV/day in the long term. Importantly, the electrodes can be simply stored in air between measurements and used directly without conditioning in solutions. With simple fabrication and free maintenance, these sensors offer a low cost and convenient alternative to bulk ISEs, especially when sample volumes or space are limited. [ABSTRACT FROM AUTHOR]