A Fluorescence Turn On-off-on Method for Sensitive Detection of Sn2+ and Glycine Using Waste Eggshell Membrane Derived Carbon Nanodots as Probe

Changes in Sn2+ 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 Sn2+ 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 Sn2+ and glycine through the specific binding between Sn2+ 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 Sn2+, the fluorescence of CDs was quenched by Sn2+ via the primary inner filter effect (IFE). However, the binding between Sn2+ and glycine prevented the IFE between Sn2+ and CDs, resulting in fluorescence recovery of CDs. Under optimized conditions, the fluorescent response of CDs displayed good linear relationships with the concentrations of Sn2+ in the range of 10-200 mu M and 200-5000 mu M, and the limit of detection (LOD) was 2.4 mu M. For glycine detection, a good linear relationship was obtained in the concentration range of 5-1000 mu M with a low LOD down to 0.76 mu M. 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 Sn2+ and glycine.

Automated summary

In this study, a fluorescence turn on-off-on strategy was developed for the rapid and sensitive detection of Sn2+ and glycine. Carbon nanodots were synthesized and used as fluorescent probes. The fluorescence of carbon nanodots was quenched by Sn2+ but recovered in the presence of glycine. The method showed good linear relationships and low limits of detection for both Sn2+ and glycine. The assay was successfully applied for glycine detection in human serum samples.