Construction And Application Of Fluorescent Sensors Based On GQDs

Graphene quantum dots（Graphene quantum dot, GQDs） is the newest member of the graphene family, and also a quasi-zero-dimensional nano fluorescent material developed the past three years. And compared to conventional semiconductor quantum dots, GQDs has good biocompatibility, low toxicity, stable performance and so on, also has broad applications in fluorescence sensing, cell labeling and biological imaging aspects. However, fluorescence sensor based on GQDs still in its infancy, there is a low fluorescence quantum yield reported in the literature, the fluorescent sensor low sensitivity and poor selectivity. Therefore, improve the synthetic conditions and design sensor system, and build high sensitivity and high selectivity of GQDs sensors is very important. The study synthesized GQDs and nitrogen-doped graphene quantum dots（N-GQDs）, Based on this, the use of graphene quantum dots as fluorescence sensors to detect tartrazine, ascorbic acid and glutathione. Results obtained from the GQDS fluorescent sensing system in application and analysis of three kinds of target provides a methodology reference and basis. Details are as follows:1 A fluorescent sensor for tartrazine based on GQDs Use Hummer method, by concentrated sulfuric acid and potassium permanganate of graphite under the condition of high temperature oxidation stripping to synthesis GO; Use the methods of TOP-down, the GO as carbon, concentrated aqueous ammonia is alkaline medium at high temperature and pressure conditions（200 ℃ 5 h）, to make the GO oxidized and broken into smaller sizes GQDs, by infrared spectroscopy（IR） and transmission electron microscopy（TEM） to characterized GQDs. The GQDs at 440 nm with a strong fluorescence, GQDs and tartrazine absorption spectrum has a large degree of overlap, we developed a new method to detect tartrazine based on the inner filter effect between them. Under optimum conditions, the linear range of tartrazine was 0.008 μmol/L⁴ μmol/L, the detection limit was 0.0035 μmol/L. compared to other quantum dots, this method has a lower detection limit and higher selectivity. Common metal ions and pigments do not interfere with the determination system, the method can be successfully used for the determination of tartrazine in drinks.2 Based on fluorescence off-on of N-GQDs-Mn O₂ system to detected AA Use the methods of Down-top, citric acid as a carbon source, ammonia as nitrogen source, hydrothermal reaction 200 ℃ 3 h to synthesis the N-GQDs, by IR, X-ray photoelectron spectroscopy（XPS）, TEM to characterized N-GQDs; Got Mn O₂ nanosheet by Na2SO₃ reduction KMn O₄, Mn O₂ nanosheet having a wide range of light absorption at N-GQDs emission peak, and have strong π-π stacking interactions between Mn O₂ and N-GQDs, N-GQDs fluorescence quenching by resonance energy transfer; AA has a strong reduction, Mn O₂ nanosheet can be reduced to Mn2+, so the fluorescence recovery. A new method for detecting AA is found. Under optimal conditions, the detection linear range for ascorbic acid was found to be from 0.02 μmol/L to 8 μmol/L, the detection limit（LOD） was calculated as 0.0056 μmol/L according to the 3σ IUPAC criteria. With respect to the reported methods, this method not only has higher sensitivity, and can eliminate common interferences in biological blood, such as uric acid（UA）, dopamine（DA）, glutathione（GSH）. the method has been successfully used to detect AA in blood sample, the recoveries is 96.5-102.7%.3 Based on fluorescence off-on of N-GQDs-Mn O₂ system to detected GSH On the basis of N-GQDs synthesis of the previous chapter, 2-（N- morphine Lin） ethyl sulfonic acid as reductant to got Mn O₂, have strong π-π stacking interactions between Mn O₂ and N-GQDs, N-GQDs fluorescence quenching by resonance energy transfer. GSH can be reduced Mn O₂ to Mn2+, fluorescence recovery. Based on this, we established a new sensor to detect GSH, compared to Na2SO₃ reduction KMn O₄, this methods has a higher selectivity for GSH. Under optimal conditions, the detection linear range for glutathione（GSH） was found to be from 0.02 μmol/L to 8 μmol/L, the detection limit（LOD） was calculated as 16 nmol/L according to the 3σ IUPAC criteria. Common metal ions, amino acids, UA and DA does not interfere with the determination of GSH, the method has been successfully used for the detection GSH in blood samples, the recoveries is 95.2-103.8%.