Chitosan-ion imprinted polymer-based Mach-Zehnder Interferometer sensors for Cd²⁺ detection using cross-linking polymerization

A Mach-Zehnder interferometer (MZI) based fiber optic sensor for the detection of cadmium ions (Cd²⁺) using chitosan-ion imprinted polymer (CS-Cd²⁺IP) coatings is presented here. The proposed sensor employs a multimode and no-core fiber (MMF and NCF) spliced between single-mode fibers (SMFs). The sensitivity of the MZI sensor is enhanced by crosslinking the chitosan polymer with epichlorohydrin (ECH) at different concentrations, forming a polymer network. The sensors exhibit varying sensitivity and selectivity ranges depending on the ECH concentration, with probe 1 achieving a range of 0 to 1 ppb (parts per billion), probe 2 from 0.01 ppb to 10 ppb, and probe 3 from 1000 ppb onwards.