Abstract: A photonic crystal fiber (PCF) based Mach-Zehnder interferometric (MZI) sensor using ion imprinted chitosan for the detection of Ni2+ ions is proposed and experimentally demonstrated. The sensor was fabricated by splicing a small section of photonic crystal fiber (PCF) between single mode fibers (SMFs). Nickel adsorbed chitosan was crosslinked with epichlorohydrin (ECH) to increase its mechanical strength and thereby to improve the sensor stability and was subsequently imprinted with Ni2+ ions. The sensor was coated with nickel ion imprinted chitosan and was examined with test solutions of various Ni2+ concentrations. The sensor exhibits a Ni2+ detection sensitivity of 0.0632 nm/μM (nanometer per micromolar) in the linear range and a limit of detection of 0.57 μM. The cross-sensitivity of the sensor was evaluated to other metal ions like Cu2+, Ca2+, and Na+ and also by comparing its performance to a sensor using non-imprinted chitosan. Results have shown better sensor response to Ni2+ ions over other metal ions and an improvement in performance over non-imprinted chitosan sensor. Investigation was also carried out to examine the effect of crosslinking on the sensor performance by varying the ECH to chitosan molar ratio (5:1, 10:1, and 15:1) and the sensor achieved its best performance when the molar ratio was 10:1
Author keywords: Ions, nickel, Refractive index, Optical fiber sensors, Sensitivity, Surface treatment, fiber-optic interferometric sensor, photonic crystal fiber, heavy metal ion sensor, Chitosan, ion imprinting