SMNS structure based fiber optic interferometer for cadmium detection

A cost-effective, easy-to-manufacture, compact, and reliable single-mode fiber/ multimode fiber/ no-core fiber/ single-mode fiber (SMNS) structure based interferometer is proposed for the detection of cadmium ions (Cd²⁺). This setup involves splicing a segment of multimode fiber (MMF) and no-core fiber (NCF) between a single-mode fiber (SMF), followed by a functionalization procedure with a composite of graphene oxide (GO)-cysteamine (MEA) and chitosan (CS)-Cd²⁺ imprinted polymer (Cd²⁺IP). The sensitivity of the sensors has been calculated by monitoring the interference minima. Three identical probes have been fabricated to ensure the duplicability and the highest sensing sensitivity is measured at -0.1211 nm/ parts per billion (ppb) in the cadmium detection range of 0 ppb to 10 ppb with a response time of 90 s. The probe demonstrates a high selectivity for Cd²⁺ compared to other heavy metal ions. The response of the probe in various pH solutions has been investigated to minimize the sensing error. Further, the temperature crosstalk is eliminated by assessing the response of a fiber Bragg grating (FBG).