Ratiometric fluorescence sensor for Fe3+ ions detection based on quantum dot-doped hydrogel optical fiber

We develop a novel ratiometric fluorescence sensor based on CdTe quantum dots (QDs) doped hydrogel optical fiber for selective and on-site detection of Fe3+ ions in real time. The hydrogel fiber is made of a core-cladding structure with a step-index profile to confine light within the core. Two types of QDs, the green emissive thioglycolic acid capped quantum dots (gQDs) and red emissive N-Acetyl-l-cysteine capped QDs (rQDs), are synthesized and incorporated in the core of the hydrogel fiber. The rQDs can be selectively quenched by the Fe3+ ions that diffuse into the hydrogel matrix while the gQDs are immune to Fe3+ ions and exhibit stable fluorescence emission. By ratiometric detection of the fluorescence intensities of the two QDs, quantitative and selective detection of Fe3+ ions is achieved in a linear range of 0-3.5 μM with a detection limit of 14 nM. The cladded hydrogel fiber doped with QDs enables efficient laser excitation and fluorescence collection in water. Our results reveal that the ratiometric sensing based on multi-QDs doped fiber can be feasibly applied for real-time and on-site analysis of heavy metal ions in aqueous environments.