Agricultural soil health monitoring using photonic crystal fiber based on combined principles of surface plasmon resonance and interferometry for lead ion detection

Abstract. To monitor the health of agricultural soil, lead (Pb2  +  ) ion measurement is essential. The various sensors for lead ion detection reported in the literature earlier are either expensive or have complicated designs. This inspired us to propose a fiber optic sensor that is simple in design, less expensive, and more efficient. A photonic crystal fiber (PCF)-unclad single mode fiber (SMF)-PCF hybrid configuration makes up the suggested sensor, and the sensing mechanism is based on a synergistic application of surface plasmon resonance and interferometry. It is shown that the suggested structure is easy to use for Pb2  +   ion detection, in addition to other advantages in limit of detection (LOD) and sensitivity. The proposed structure is optimized to attain a LOD of 8.32  mg  /  kg, which is much less than the permissible limit of Pb2  +   ions permitted in healthy agricultural soil, i.e., 100 to 400  mg  /  kg. Additionally, a polymer that is attached atop the gold layer and to which only Pb2  +   ions can adhere ensures the sensor’s specificity. To the best of our knowledge, our proposed optical fiber-based sensor design and approach adopted to detect lead ions in agricultural soil are the first of their kind.