| Carbon quantum dots,with strong photoluminescence,excellent water solubility,low toxic and anti-photobleaching,have been applied in various areas,such as fluorescence sensing,bio-imaging,optoelectronic devices.Compared to macroscopic carbon(low water solubility,black matter),there are abundant hydrophilic groups on the surface of carbon quantum dots so that they can be well dispersed in water.The photoluminescence of carbon quantum dots could be quenched by electron donor or acceptor,which lays the foundation for the detection of target substances based on the fluorescence regulation of carbon quantum dots,especially the most widely used in metal ion sensing.For further expanding the application of carbon quantum dots in analytical detection,nitrogen-doped carbon quantum dots and carbon dots with red fluorescence emission were prepared in this research.According to properties of analytes,an appropriate quencher was selected.Two types of fluorescence recovery sensors were conducted based on NCQDs/Hg2+complex system and R-CQDs/Ru(bpy)2(dppz)2+complex system.These sensors can be used for indirectly determination of non-fluorescent substances,including thiourea and DNA.The concrete content is as follows:1)Based on the recovery of the fluorescence of Hg2+ quenched carbon quantum dots by thiourea,a fluorescence analysis method for thiourea was established.Nitrogen-doped carbon quantum dots(NCQDs),with 17%of quantum yield and high selectivity for Hg2+,were synthesized by one-step hydrothermal method,using ammonium citrate and dextrin as carbon source and nitrogen source,respectively.Then,we characterized above NCQDs using UV,FL,IR,XPS and HR-TEM.The results indicated that NCQDs were spherical particles with good dispersion.Also,there were rich in functional groups on the surface of carbon quantum dots,such as-COOH,-OH,-CONH-,etc.Due to the fluorescence of NCQDs selectively quenched by Hg2+,the fluorescence of NCQDs can be restored based on the strong interaction between thiourea and Hg2+.There was a good linear relationship between the recovered fluorescence and the concentration of thiourea within range of 0.900×10-6 mol L-1～10.0×10-6 mol L-1 and the detection limit for thiourea detection was 0.150×10-6 mol L-1.This method can be applied for the determination of thiourea in tab water,lake water,and rice flour and the spike recoveries were between 91.6 and 108%.The quenched mechanism of Hg2+ towards the FL signal of carbon dots was discussed.The results demonstrated that the quenched mechanism was a static quenching process.2)Based on the recovery of the fluorescence of Ru(bpy)2(dppz)2+complex quenched carbon quantum dots by DNA,the fluorescence analysis method of DNA was proposed.Using glutathione and formamide as raw materials,carbon quantum dots were prepared by a solvothermal method.The carbon dots(R-CQDs)had dual emission characteristic,one of which was red fluorescence emission(683 nm).Then,the morphology and spectral properties of R-CQDs were characterized by UV-vis,FL,IR and HR-TEM.In addition to-OH and-COOH,R-CQDs might have sulfur-containing functional groups because of different raw materials used.The fluorescence of R-CQD can be quenched by the Ru(bpy)2(dppz)2+complex with"light switch" properties of nucleic acid molecules.Because Ru(bpy)2(dppz)2+had a strong specificity with DNA.When DNA was added to a mixed solution of R-CQDs and Ru(bpy)2(dppz)2+complex,the fluorescence(683 nm)of R-CQDs could be significantly restored.Thus,a quick,highly selective and sensitive method was established for DNA detection.Under the optimum conditions,there was a good linear relationship between the degree of fluorescence recovery of carbon quantum dots and DNA concentration in range of 0.0150～9.60 μg·mL-1.The detection limit was 0.00536 μg·mL-1.This sensor can be used for DNA detection in synthetic sample with recoveries in range of 97.4～106%.Compared to detecting DNA with Ru(bpy)2(dppz)2+directly,the fluorescence of R-CQDs was stronger and the sensor had higher sensitivity. |
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