Trace detection of cadmium (II) ions based on an air-hole-assisted multicore microstructured optical fiber

Cadmium ion (Cd2+) is one of the most crucial industrial pollutants that cause serious harm to the human body. For rapidly and sensitively determining the concentration of Cd2+ in a solution in real time, a highly selective Cd2+ sensor with high sensitivity is proposed based on a multimode interference effect in an air-hole-assisted multicore microstructured optical fiber (AA-MCF). Seven large air holes in an AA-MCF isolate of six fiber cores; one of them is cut open to expose two adjacent cores and form a microfluidic channel. It can be used as the region where the analyte liquid interacts with light. When the refractive index in this region varies, the multimode interference effect is influenced, so that the refractive index of the analyte can be quickly observed. Quantification is achieved by calculating the Cd2+ concentration through the refractive index. Theoretical and experimental results show that the sensitivity of this sensor made of an AA-MCF can reach 7.443 × 109 nm/(mol/L) and the experimental limit of detection is 6.0 × 10–12 mol/L. The proposed sensor exhibits high stability, specificity, and a compact structure, offering promising potential for biochemical sensing applications, such as environmental monitoring and disease diagnosis.