Detection of Ni2+ with optical fiber Mach-Zehnder interferometer coated with chitosan/MWCNT/PAA

An optical fiber Nickel ions (Ni
²⁺
) sensor based on a Mach-Zehnder interferometer (MZI) formed by cascading two coating-functionalized fiber tapers is proposed and experimentally demonstrated. The functional coating is a multi-layer film of chitosan/muli-walled carbon nanotubes (MWCNT)/poly acrylic acid (PAA) formed directly onto the fiber surface via a layer-by-layer assembly technique. As the heavy metal ions get absorbed by the coating, transmission spectra of the MZI sensor changes due to refractive index variation of the coating. A high sensitivity of 56.5 dB/mM is achieved for concentration of Ni
²⁺
ranging from 0.3 to 0.7 mM.