Annular micro-nano optic fiber sensor based on α-Fe2O3@SiO2@CS imprinting for Cu(II) ion detection

Sensors for the rapid and easy detection of copper ions (Cu²⁺) are crucial in drinking water and healthcare. However, this research is still challenging, such as more complicated sample pretreatment and longer detection time. In this paper, a highly sensitive optic fiber sensor for trace detection of Cu²⁺ in aqueous solution is proposed. Based on the principle of intermodal interference, the coating method of surface functionalization of functional groups is adopted, and the single-mode fiber (SMF) is bent to form an annular structure to enhance the interference, and the cone pulling machine is used to perform cone pulling treatment before coating a uniform layer of α-Fe₂O₃@SiO₂@CS nanocomposite imprinted material. The amino and hydroxyl groups have specific recognition functions for Cu²⁺ and can chelate with Cu²⁺, thus changing the refractive index of the material, which in turn makes the interference spectrum shifted. Furthermore, Cu²⁺ is chosen as the template ion to make ion-imprinted materials, and the trace detection of Cu²⁺. The results showed that the interference spectrum was red-shifted with the increase of Cu²⁺ concentration in the range of 0–1 μM with a concentration dependence coefficient of 3.35 nm/log·μM, and the maximum detection sensitivity of Cu²⁺ reached 1232.52 nm/μM with a good linearity of 0.994. The selectivity of Cu²⁺ was more than 70 times that of other ions. In addition, the sensor has the advantages of fast response time, high stability, good reproducibility, simple fabrication and low cost.