A Fluorescence Turn On–off-on Method for Sensitive Detection of Sn 2+ and Glycine Using Waste Eggshell Membrane Derived Carbon Nanodots as Probe

Changes in Sn 2+ and glycine levels are relevant to many important physiological procedures in human health. However, investigation of their physiological functions is limited because few versatile methods towards Sn 2+ and glycine detection have been developed. In this work, a fluorescence turn on–off-on strategy was firstly constructed for rapid and sensitive detection of Sn 2+ and glycine through the specific binding between Sn 2+ and glycine. Carbon nanodots (CDs) with a quantum yield of 19.5% were synthesized by utilizing inner film of waste eggshell as carbon source and employed as fluorescent probe. In the presence of Sn 2+ , the fluorescence of CDs was quenched by Sn 2+ via the primary inner filter effect (IFE). However, the binding between Sn 2+ and glycine prevented the IFE between Sn 2+ and CDs, resulting in fluorescence recovery of CDs. Under optimized conditions, the fluorescent response of CDs displayed good linear relationships with the concentrations of Sn 2+ in the range of 10–200 µM and 200–5000 µM, and the limit of detection (LOD) was 2.4 µM. For glycine detection, a good linear relationship was obtained in the concentration range of 5–1000 µM with a low LOD down to 0.76 µM. Moreover, the practicability of the assay was also demonstrated by measuring glycine content in human serum samples. This work provides an economical, green and fast method for biological analysis of Sn 2+ and glycine.