Cadmium-ion detection: a comparative study for a SnO2, MoS2, SnO2/MoS2, SnO2-MoS2 sensing membrane combination with a fiber-optic Mach-Zehnder interferometer.

Abstract

A novel fiber-optic Mach-Zehnder interferometer based on SnO2, MoS2, SnO2/MoS2, and SnO2-MoS2 sensing film for cadmium-ion (Cd2+) detection is proposed and fabricated. The photonic-crystal fiber (PCF) is sandwiched between the no-core-fiber-1 (NCF1) and no-core-fiber-2 (NCF2), forming the Mach-Zehnder interferometer with the NCF1-PCF-NCF2 structure, which is regarded as the sensing unit. The SnO2, MoS2, SnO2/MoS2, and SnO2-MoS2 sensing films are, respectively, coated on the surface of two NCFs claddings. The comparative experiment results of the sensors with four membranes (SnO2, MoS2, SnO2/MoS2, SnO2-MoS2) show that the sensors have good sensing performance for Cd2+ in the concentration range of 0-100 µM. When these sensing films adsorbed Cd2+, the monitoring wavelength shows blueshift of 0.6931 nm, 1.0252 nm, 1.9505 nm, respectively, and redshift of 3.0258 nm, and the sensitivities are 6.931 pm/µM, 10.252 pm/µM, 19.505 pm/µM, and 30.258 pm/µM, respectively. The sensor with SnO2-MoS2 bilayer film exhibits the optimal response to Cd2+ with excellent selectivity and stability. The proposed sensor has the advantages of simple structure, easy fabrication, small size, etc., having potential application in the monitoring of Cd2+ in aqueous solution.