Ratiometric Fluorescence Optical Fiber Sensing for On-Site Ferric Ions Detection Using Single-Emission Carbon Quantum Dots

A carbon quantum dots (CQDs)-based ratiometric fluorescence fiber sensing method for Fe ³⁺ on-site detection is developed. In the proposed ratiometric sensing system, only one kind of single-emission fluorescent material is used. The method of ratiometric sensing provides correction for environmental interferences and eliminates the fluctuations caused by the light source. In this sensing system, the LED light source is not only used to supply the light for excitation, but also provide the internal standard for ratiometric sensing. The CQDs are synthesized by a simple hydrothermal method and can be immobilized on the fiber easily in seconds without molds. The designed annular fiber tip has the advantages of high-efficiency collection of fluorescence and long service life. It is found that concentration of ferric ions can be detected in the range of 0-40 μM by the sensing system. The limit of detection (LOD) is as low as 0.3 μM, which is close to the LOD obtained by dispersing the carbon quantum dots in the solution. The response time is only 6 seconds. The sensing probe with the rapid response is only 4 mm in length with the maximum diameter of 350 μm, showing great potential on real-time detection in narrow area. The practicability and reliability of the present system is verified by actual samples.