Ultra-sensitive optical fiber sensor based on intermodal interference and temperature calibration for trace detection of copper (II) ions

Abstract

An ultrahigh sensitive optical fiber sensor for trace detection of Cu²⁺ concentration in aqueous solution with temperature calibration has been developed in this article. Based on the intermodal interference, the sensor is coated with a hydrogel sensing membrane with specific binding to Cu²⁺ on the no-core fiber/single mode fiber/no-core fiber structure by using our new spray coating method. The imidazole group in the sensing film combines with Cu²⁺ to produce chelation, which changes the refractive index of the sensing film. The Cu²⁺ at trace concentration can be detected by monitoring the displacement of the interference trough. The experimental limit of detection of 3.0×10^-12 mol/L can be achieved with the spectral resolution of 0.02 nm. The sensor has also long-term stability of the concentration measurement with the average standard deviation of 1.610×10^-12 mol/L over 2 hours observation time and can be compensated the influence of ambient temperature on concentration detection by conducting the temperature calibration. In addition, the sensor has the advantages of strong specificity, simple fabrication and low cost.