Evanescent wave sensor for potassium ion detection with special reference to agricultural application

We are introducing 4′-aminodibenzo-18-crown-6 ether (A2BC) modification of gold nanoparticles coated optical fiber as a new sensor for evanescent wave trapping on the polymer optical fiber to detect low-level potassium ions. We characterized these gold nanoparticles by X-ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Nanoparticle tracking analysis (NTA), Field Emission scanning electron microscopes (FE-SEM), and UV–Visible spectroscopy. In the present study, we modified the gold nanoparticles with A2BC for selective sensing of potassium (K+) ions. The interaction between A2BC and K+ ions leads to the temporary formation of a sandwich structure as crown ethers form steady complexes with metal ions. This sandwich structure leads to potassium detection. In our implementation, related operational parameters such as cladding length, roughness, and concentration of A2BC and gold nanoparticles, were optimized to achieve a detection threshold of 1 ppm. Additionally, we optimized the optical fiber sensor to increase its detection sensitivity from the μV range to the mV range. The sensor demonstrates a fast response time (10 s) and high sensitivity, selectivity, and stability, which cause a wide linear range (1–100 ppm) and a low limit of detection (LOD = 0.14 ppm). Lastly, we tested the sensor for a soil-sensing application.