Chitosan/PAA based fiber-optic intermodal sensor for nickel cation
Long, Cassie Huiyi
Date of Issue2015
School of Chemical and Biomedical Engineering
A Fabry–Pérot and an in-fiber Mach-Zehnder fiber interferometer for heavy metal: nickel cation (Ni2+) detection are proposed and experimentally demonstrated. The Fabry–Pérot interferometer fabricated by tapering and micro-hole drilling shows the relationship between reflection signal of the sensor and environmental refractive index is dependent on the size of the micro-hole, such that the closer the micro-hole size is to the core of the sensor the better the sensitivity. In the experiment, a sensor with micro-hole size of 0.5 x7 x9 has obtained a good refractive index sensitivity of -34.55 2.2067nm/RIU. However, due to the poor repeatability the sensor is unable to be employed for the nickel ion detection. Hence, the intermodal Mach-Zehnder interferometer is proposed, the sensor was formed by a sensor length of 4 cm no-core fiber (NCF) sandwiched between two short sections of lead-in/lead-out single-mode fiber (SMF) i.e., SMF-NCF-SMF. A distinct interference pattern is obtained due to the fiber-core mismatch and core-cladding modes interference. The selected interference dip is extremely sensitive to the external refractive indexes, providing a stable refractive index response with sensitivity up to 550.90 nm/RIU. To facilitate the Ni2+ sensing, the NCF based Mach-Zehnder interferometer sensor was functionalized with chitosan (CS) and polyAcrylic Acid (PAA) multilayer film, denoted as [CS/PAA]n where n is number of bilayer, through electrostatic self-assembly. The self-assembly film provides ample Ni2+ adsorption sites which chelate Ni2+ forming a complex and densify the film, thus, refractive index of the film is increased resulting a phase shift of the interference spectrum of the sensor. By calibrating the relationship of Ni2+ concentration with wavelength shift of the sensor, the sensor exhibits a high sensitivity of 0.01434nm/µM with good repeatability and stability, proving itself to be an excellent candidate for the nickel ion detection in rivers, lakes or even drinking water.
Final Year Project (FYP)
Nanyang Technological University