The Fluorescent Quenching Mechanism of N and S Co-Doped Graphene Quantum Dots with Fe3+ and Hg2+ Ions and Their Application as a Novel Fluorescent Sensor.

Yue Yang,Zhezhe Wang,Tong Zou,Sijia Peng,Xinxin Xing,Yude Wang,Xu Zhang,Rongjun Zhao

doi:10.3390/nano9050738

Abstract

The fluorescence intensity of N, S co-doped graphene quantum dots (N, S-GQDs) can be quenched by Fe3+ and Hg2+. Density functional theory (DFT) simulation and experimental studies indicate that the fluorescence quenching mechanisms for Fe3+ and Hg2+ detection are mainly attributed to the inner filter effect (IFE) and dynamic quenching process, respectively. The electronegativity difference between C and doped atoms (N, S) in favor to introduce negative charge sites on the surface of N, S-GQDs leads to charge redistribution. Those negative charge sites facilitate the adsorption of cations on the N, S-GQDs’ surface. Atomic population analysis results show that some charge transfer from Fe3+ and Hg2+ to N, S-GQDs, which relate to the fluorescent quenching of N, S-GQDs. In addition, negative adsorption energy indicates the adsorption of Hg2+ and Fe2+ is energetically favorable, which also contributes to the adsorption of quencher ions. Blue fluorescent N, S-GQDs were synthesized by a facile one-pot hydrothermal treatment. Fluorescent lifetime and UV-vis measurements further validate the fluorescent quenching mechanism is related to the electron transfer dynamic quenching and IFE quenching. The as-synthesized N, S-GQDs were applied as a fluorescent probe for Fe3+ and Hg2+ detection. Results indicate that N, S-GQDs have good sensitivity and selectivity on Fe3+ and Hg2+ with a detection limit as low as 2.88 and 0.27 nM, respectively.

Highlights

Graphene quantum dots (GQDs) have drawn research interest by reasons of their excellent photoluminescence, low toxicity, and good biocompatibility [1]
Diffusive encounters collision contact can be attributed to the dynamic quenching process, while new complex forms can be assigned to the static quenching process [8]
Density functional theory (DFT) and experimental studies indicate that non-radiative electron transfer between Hg2+ cations and N, S-GQDs cause dynamic fluorescence quenching

Summary

Introduction

Graphene quantum dots (GQDs) have drawn research interest by reasons of their excellent photoluminescence, low toxicity, and good biocompatibility [1]. They have been applied in various fields, such as solar cells, light-emitting diodes, bioimaging, and fluorescent sensors [2]. According to the interaction between quantum dots and a quencher, the main quenching mechanism can be divided into Förster resonance energy transfer (FRET), the inner filter effect (IFE), and the dynamic and static quenching process [6,7]. The quenching process requires sufficient contact between quantum dots and a quencher. Diffusive encounters collision contact can be attributed to the dynamic quenching process, while new complex forms can be assigned to the static quenching process [8]

Methods

Results

Conclusion