Highly sensitive fiber optic sensor based on chitosan/α-Fe2O3 for trace copper(II) ion detection.

• A new nanocomposite material (CS/α-Fe 2 O 3) is proposed for the specific identification and detection of copper ions. • The specificity of the CS/α-Fe 2 O 3 nano-composite and the response performance of the fabricated interference fiber sensor were explored and analysed. • High sensitivity measurement of Cu2+ concentration (0–1 μM) was achieved. Instrument methods are essential for simple and rapid detection of copper(II) (Cu2+) in drinking water and healthcare. However, these methods suffer from complex sample pretreatment and long detection time. This paper proposed a highly sensitive fiber optic sensor for trace Cu2+ detection in aqueous solutions. Based on the principle of modal interference, by surface functionalization, a uniform chitosan (CS)/α-Fe 2 O 3 nanocomposite material was coated on a structure of no-core fiber–multimode fiber–no-core fiber (NCF1-MMF-NCF2). The amino and hydroxyl groups in the material have a specific recognition function for Cu2+, which can chelate with Cu2+ and change the refractive index of the material, leading to the shift of interference spectrum. Trace Cu2+ detection can be achieved by monitoring the displacement of the interference spectrum. The results revealed that within the range of 0–1 μM Cu2+ concentrations, with increasing Cu2+ concentration, the interference spectrum underwent a red shift and the maximum detection sensitivity of Cu2+ ions reached 456.69 nm/μM, with a good linearity of 0.989. Also, the sensor has the advantages of high stability, good repeatability, simple fabrication, and low cost. [ABSTRACT FROM AUTHOR]