Portable multiplexed ion-selective sensor for long-term and continuous irrigation water quality monitoring

In agricultural contexts, the demand for continuous and precise measurement of multiple ions is crucial. While arrays of solid-contact ion-selective electrodes (SCEs) have been developed previously, there has been limited emphasis on their continuous and long-term monitoring of ions. Addressing this gap, our work introduces an innovative sensor array utilizing Ni-HAB MOF as an ion-to-electron transducer, enabling real-time detection of nitrate, potassium, and pH levels. The sensors exhibit exceptional stability, eliminating the need for frequent recalibration. For instance, the K⁺-selective sensor displays an unprecedentedly low potential drift of 0.05 µV/h, surpassing existing solid-contact sensors by two orders of magnitude. Similarly, the pH sensor demonstrates a drift of 0.3 µV/h, outperforming competitors by a factor of 100. The NO₃^--selective sensor shows minimal drift at 0.5 µV/h, surpassing comparable sensors by a factor of ten. Additionally, the K⁺-selective sensor features a sensitivity of 57.8 mV/dec and a LOD of 1.9 µM, while the NO₃^--selective sensor offers a sensitivity of 56.8 mV/dec and a LOD of 6.23 µM. Integrated into a portable array with wireless data transmission, this system enables real-time water quality monitoring in remote areas. Rigorous testing of the developed sensor array in a tailored complex agricultural solution confirms its selective response to target ions even in the presence of interfering ions. Importantly, pH fluctuations do not compromise the precision of the K⁺ and NO₃^-- selective sensors, highlighting the system's robustness in real-world agricultural settings.