| Graphene quantum dot is zero-dimensional carbon material with a size of less than 10nm.It is widely used in optical sensing,electrochemiluminescence sensing,electrochemical sensing,biological imaging,catalysis,antibacterial and other fields with unique optical and electrical properties.At present,graphene quantum dot has some limitations such as single function,low catalytic activity,single wavelength emission and weak fluorescence intensity.Therefore,it is particularly important to design and prepare graphene quantum dots with good fluorescent properties and functions.In this paper,graphene quantum dots were functionalized by introducing functional groups or functional components.Serine-functionalized graphene quantum dot,Serine-and histidine-functionalized graphene quantum dot,Glutamic acid-and histidine-functionalized graphene quantum dot and Serine-functionalized graphene quantum dot/NaYF4:Yb,Er,Tm complex were prepared.The applied researches of functionalized graphene quantum dots in the fields of analysis,catalysis and cell imaging have been carried out.Citric acid as carbon source,serine,histidine and glutamic acid as functional reagents,serine-functionalized graphene quantum dot,serine-and histidine-functionalized graphene quantum dot,glutamic acid-and histidine-functionalized graphene quantum dot were prepared by pyrolysis.The diameter of the functionalized graphene quantum dots is about 3 to4 nm,the thickness is about 3 layers.There are rich functional groups on the surface.The fluorescence intensity of serine-functionalized graphene quantum dot prepared by introducing serine into the surface of graphene quantum dot is 3.15 times that of graphene quantum dot.On the basis of the introduction of serine molecules,histidine was introduced as a functional molecule to obtain serine-and histidine-functionalized graphene quantum dot with dual fluorescence emission.When the serine/citric acid molar ratio is 0.2,the serine and histidine functionalized graphene quantum dot has two obvious fluorescence emission peaks under excitation at 360 nm;the yellow fluorescence is strong under excitation at 485 nm.In order to enrich the functions of the graphene quantum dot,the introduction of glutamic acid and histidine on the surface of the graphene quantum dot not only increases the fluorescence intensity of the graphene quantum dot,but also enhances the peroxidase-like activity.Glutamic acid-and histidine-functionalized graphene quantum dot can catalyze H2O2 to produce?OH and oxidize 3,3',5,5'-tetramethylbenzidine.The Michaelis constant of glutamic acid-and histidine-functionalized graphene quantum dot with H2O2 is 1.11 mmol/L.The preparation of functionalized graphene quantum dots has laid a solid foundation for applied research.Serine-functionalized graphene quantum dot is used as fluorescent probe.Based on the inner filter effect between serine-functionalized graphene quantum dot and Cr(VI),a method was developed for determination of Cr(VI).When the p H of the medium is 7.4,the detection system has the largest fluorescence response value.The linear concentration range of this method is 0?mol/L?500?mol/L,the detection limit is 0.0033?mol/L.It has a wide linear range and high sensitivity.The addition of other ions will not affect the fluorescence of serine-functionalized graphene quantum dot.It has good selectivity.This method has been successfully used for the detection of Cr(?)in environmental water.Serine-and histidine-functionalized graphene quantum dot shows unique double fluorescence emission.The ultraviolet-light excitation at a wavelength of 360 nm produces strong blue emission,while visible-light excitation at a wavelength of 485 nm produces stronger yellow emission.The blue emission and yellow emission were used for fluorescence detection of carbendazim coupled with DNA recycling amplification and cell imaging,respectively.One carbendazim molecule leads to formation of many G-quadruplex/hemin DNAzyme by target-induced DNA recycling.With this DNAzyme as catalyst,o-phenylenediamine is oxidated into the fluorescent oxidation product 2,3-diaminophenazine and achieves suitable signal amplification.The 2,3-diaminophenazine molecule interacts with Serine-and histidine-functionalized graphene quantum dot probe and results in the obvious fluorescence quenching of Serine-and histidine-functionalized graphene quantum dot,which further improves the detection signal.The linear range of the sensing platform is 1.0×10-16mol/L?1.0×10-9 mol/L,and the detection limit is 6.1×10-17 mol/L.The analytical method was successfully used for the fluorescence detection of carbendazim in tomato samples.The rare-earth upconversion nanomaterial(NaYF4:Yb,Er,Tm)were used as functional component to functionalize serine-graphene quantum dot,and serine-functionalized graphene quantum dot/NaYF4:Yb,Er,Tm complex is prepared.The size of the complex is about 25 nm.And the surface is rich in functional groups.The up-conversion luminescence of NaYF4:Yb,Er,Tm can be enhanced with the ability of serine-functionalized graphene quantum dot.Serine-functionalized graphene quantum dot as an antenna to absorb more photons and transfer energy to NaYF4:Yb,Er,Tm.Since the surface of the complex contains a large number of carboxyl groups,it can coordinate with Fe(?),which causes the upconversion fluorescence of the complex be quenched.Based on this fluorescence quenching phenomenon,the complex is used as a fluorescent probe to establish a method for determination of Fe(?).The linear range of this method is 1×10-8 mol/L?3×10-4 mol/L.And the detection limit of the method is 6.7×10-9 mol/L.This method has good selectivity and sensitivity.The method has been successfully used for the detection of Fe(?)in human serum. |
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