Fe3+ Sensing Based on Hydrogel Optical Fiber Doped with Nitrogen Carbon Dots

In this paper, a nontoxic and biocompatible hydrogel optic fiber Fe3+ sensor is presented. Nitrogen carbon dots (NCDs) as fluorescence indicators are prepared by a one-step hydrothermal method using citric acid as the carbon source and urea as the nitrogen source. Transmission electron microscopy images and x-ray diffraction analysis show that the average size of the NCDs is 3.94 nm, and they have an amorphous structure. X-ray photoelectron spectroscopy shows that nitrogen is effectively doped into the framework of the NCDs. The hydrogel optical fiber with a core-cladding structure is fabricated using different concentrations of polyethylene glycol diacrylate as precursor. The NCDs were incorporated into the core of the hydrogel fiber for Fe3+ sensing. NCDs were selectively quenched by Fe3+ diffused into the hydrogel fiber. The sensitivity of the system was optimized by varying the concentration of doped NCDs. The fluorescence intensity decreased with the increase in temperature, with the greatest sensitivity at 24°C. By measuring the fluorescence intensity, the quantitative and selective detection of iron ions was realized in the range of 0–60 um, and the detection limit was 0.802 um. It has good application prospects in the detection of Fe3+ and can realize the detection of implanted biological Fe3+ in vivo.