Chitosan/PAA based fiber-optic intermodal sensor for nickel cation

• Main Author: Long, Cassie Huiyi
• Other Authors: Chan Chi Chiu
• Format: Final Year Project
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Bioengineering
• Online Access: http://hdl.handle.net/10356/65188
• Institution: Nanyang Technological University

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.