Ion sensing in agricultural and food applications: a critical review of solid-contact ion-selective sensors.

Solid-contact ion-selective electrodes (SC-ISEs) have gained prominence as versatile tools for monitoring ionic species in complex agricultural and food matrices, offering low-cost, miniaturizable, and field-deployable alternatives to conventional laboratory assays. This review critically examines electrochemical transduction techniques for SC-ISEs, including potentiometry, coulometry, amperometry, voltammetry, and electrochemical impedance spectroscopy. By evaluating these techniques based on their detection mechanisms, sensitivity ranges, selectivity characteristics, and application potential, we highlight how dynamic electrochemical modes can overcome potentiometry limitations. Emphasis is placed on the role of solid-contact design, nanostructured materials (e.g., conducting polymers, carbon nanomaterials, and laser-induced graphene), and integrated readout strategies that enhance sensor performance in real-world applications. We also analyze state-of-the-art configurations for ion detection in soil, water, and food products. Finally, we discuss current challenges and offer perspectives on SC-ISEs integration into cyber-physical systems, where real-time, connected, and autonomous sensing will be central for sustainable agriculture and food systems, while also addressing regulatory considerations.