Preparation Of Doped Graphene Quantum Dots And Its Application In Fluorescence Sensing

Graphene quantum dots?GQDs?are zero-dimensional fluorescent carbon nanomaterials with a lateral dimension of less than 100 nm and a thickness of less than 10 layers.GQDs have the advantages of good water dispersibility,good biocompatibility,low cytotoxicity and stable photoluminescence.Thus,GQDs exhibit potential applications in fluorescence sensing,biological imaging and other fields.Doping of GQDs with hetero atom can change the structure and electronic properties of GQDs.Consequently,it is an effective means to regulate the properties of GQDs for improving the fluorescence quantum yield and increasing the active sites.In this thesis,two kinds of heteroatom-doped graphene quantum dots were prepared by simple one-step hydrothermal synthesis methods.The properties of hetero atom doped GQDs were characterized and their applications in the detection of metal ions,small molecules and biomolecules were investigated.?1?A one-step hydrothermal preparation method for boron-doped graphene quantum dots?B-GQDs?was established,and the application of B-GQDs in the detection of Fe³⁺ions,Cyt C and Pi was also investigated.B-GQDs were prepared by one-step hydrothermal method using 1,3,6-trinitropyrene as carbon source,borax as boron source and NaOH solution as reaction medium.B-GQDs could be stably dispersed in water and emit bright yellow-green fluorescence under 365 nm UV light.The fluorescence spectra show that the maximum excitation wavelength of B-GQDs is480 nm and the maximum emission wavelength is 520 nm.The fluorescence emission is non-excitation dependent with absolute quantum yield of 16.8%.The morphology and structure of B-GQDs were characterized by transmission electron microscopy and atomic force microscopy.The results show that B-GQDs have a uniform lateral dimension with an average particle size of 2.0nm and a thickness of about 1.0-1.2 nm with single or double layer graphene-layered structure.X-ray photoelectron spectroscopy was used to investigate the elemental composition of B-GQDs.The results proved the successful doping of B.The selectivity of B-GQDs towards different metal ions was investigated and Fe³⁺could significantly quench the fluorescence of B-GQDs.Based on this principle,a method for detecting Fe³⁺with B-GQDs as a fluorescent probe was established?turn-off mode?.The linear range of B-GQDs for detecting Fe³⁺was 0.05-220?M and 220-420?M with a limit of detection?LOD?of 31.2 nM.Due to the presence of iron porphyrin structure,cytochrome C?Cyt C?could also quench the fluorescence of B-GQDs.Turn-off fluorescence detection of Cyt C method was established with linear range of 10-300?g/ml and 300-2000?g/ml.The LOD was 5.9?g/ml.In the B-GQDs-Fe³⁺system,the fluorescence of B-GQDs was quenched.After the addition of phosphate?Pi?,Fe³⁺is released from B-GQDs due to the stronger binding ability of Fe³⁺to the oxygen-containing functional groups on Pi.Thus the fluorescence of B-GQDs recovered.Indirect detection of Pi based on B-GQDs-Fe³⁺system?turn-off-on mode?was established.The linear range of detection Pi was 3-40?M with LOD of 0.34?M.In addition,the detection performance of Fe³⁺in the actual sample was evaluated by the spike recovery method.?2?A one-step hydrothermal preparation method of nitrogen-doped graphene quantum dots?N-GQDs?was established and their application in the detection of Hg²⁺ions and L-cysteine?L-Cys?was investigated.N-GQDs were prepared by one-step hydrothermal method using 1,3,6-trinitroguanidine as the carbon source,L-tryptophan as the nitrogen source and NaOH aqueous solution as the reaction medium.The as-prepared N-GQDs were stably dispersed in water and emitted bright blue fluorescence under 365 nm with the maximum excitation wavelength of 370nm and the maximum emission wavelength of 445 nm.N-GQDs had an average particle size of2.1 nm and a thickness of 1.0-1.3 nm with a single or double layered graphene structure.XPS characterization proved the successful doping of N elements.The selectivity of N-GQDs towards different metal ions was investigated.It was found that Fe³⁺,Cu²⁺and Hg²⁺could significantly quench the fluorescence of N-GQDs.With tartaric acid as a masking agent,the interaction of Fe³⁺and Cu²⁺with N-GQDs can be masked.Thus,fluorescent detection of Hg²⁺by N-GQDs was achieved with a linear range detection of 0.05-15?M and an LOD of 19.6 nM.It was found that addition of L-Cys can destroy the interaction between Hg²⁺and N-GQDs and recover the fluorescence.Indirect detection of L-Cys with a linear range of 0.1-30?M?LOD of 29.2 nM?was achieved.