Ion-Imprinted Chitosan-Based Interferometric Sensor for Selective Detection of Heavy Metal Ions

A photonic crystal fiber (PCF)-based Mach-Zehnder interferometric 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 the PCF between single-mode fibers. 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 nonimprinted chitosan. Results have shown better sensor response to Ni2+ions over other metal ions and an improvement in performance over a nonimprinted chitosan sensor. Investigation was also carried out to examine the effect of crosslinking on the sensor performance by varying the ECH to the chitosan molar ratio (5:1, 10:1, and 15:1) and the sensor achieved its best performance when the molar ratio was 10:1.