Flexible MoS$_{2}$-Based Ion-Selective Sensor With Valinomycin Membrane for In Situ Detection of Soil Potassium (K$^+$) Ions

In this work, we report the flexible MoS$_{2}$/Valinomycin-based sensor for in-situ$\rm {K^+}$detection in the soil sample. The fabricated sensor, realized on a flexible PET substrate using scalable ink-dispensing techniques, exhibits a wide detection range of 1-100 mM with high linearity ($R^{2}$= 0.9975), and sensitivities of 5.6$\mu$A/mM in analyte solution and 2.1$\mu$A/mM in soil sample. More importantly, cyclic voltammetry analysis reveals stable and reversible oxidation-reduction behavior across repeated cycles, with excellent reproducibility in multiple sensor replicas. The fabricated sensor uniquely combines soil compatibility, flexibility, reproducibility, and cost-effective fabrication, which addresses the critical gap between laboratory sensing technologies and field-deployable soil nutrient monitoring. These results establish the MoS$_{2}$/Valinomycin sensor as a robust and scalable platform for precision agriculture, with the potential to advance real-time nutrient management and promote sustainable farming practices.