Wearable and field deployable ion sensors for continuous environmental and health monitoring

Ion-selective sensors have progressed from laboratory instruments toward field-deployable and wearable devices through advances in flexible materials, scalable fabrication, low-power electronics, and wireless communication. This critical review examines field and wearable ion sensors for real-time environmental and health monitoring, with emphasis on soil nutrient monitoring, seawater-quality assessment, and sweat analysis. It discusses substrate materials (including PDMS, PET, and graphene-based materials), fabrication methods (direct ink writing, chemical vapor deposition, and three-dimensional printing), and multilayer device architectures comprising flexible substrates, electrodes, ion-selective membranes, microfluidics, signal conditioning, and wireless transmission. Environmental sensing approaches are grouped into electrochemical, dielectric/electromagnetic, optical/spectroscopic, and plant-wearable platforms. Marine platforms are compared with particular attention to biofouling, while sweat-sensing examples include optical watches, battery-free NFC patches, flexible carbon-based patches, and multivariate correction strategies. Wireless technologies are evaluated in terms of range, energy demand, and data rate. A critical laboratory-to-field comparison is presented across seven criteria, followed by six recent case studies (2023–2026). The available evidence indicates that field and wearable sensors remain limited by potential drift, reference-electrode instability, matrix effects, mechanical perturbation, and biofouling. No reported platform simultaneously demonstrates high analytical performance, effective antifouling, long-term stability, low power consumption, and robust wireless operation under realistic conditions. Priorities for translation include durable reference systems, validated antifouling and cleaning strategies, multivariate drift correction, interoperable IoT architectures, and safer, more sustainable materials.