Preparation Of Carbon Dots And Its Application In Food Detection

The most obvious advantages of fluorescent probe are simple equipment,simple operation,short response time and high sensitivity.At present,more and more scholars begin to research and design fluorescent nanoprobe and try to apply it to more fields,such as biosensor,environmental,biochemical analysis and food detection.Among them,carbon nanodots(CDs),as a new type of fluorescent nanomaterials,have become more and more popular in recent years.Compared with traditional quantum dots and organic dyes,CDs have the advantages of low toxicity,biocompatibility and photobleaching resistance.These advantages have greatly improved the possibility of using CDs in related fields,such as real-time bioimaging and food safety monitoring.In recent years,scholars have synthesized various kinds of CDs by different methods or different raw materials.The properties of these CDs are similar or different.Most of the properties of CDs are that the emission wavelength of CDs depends on the excitation wavelength.However,there is no clear conclusion about the specific mechanism of CDs.It is concluded that these properties of CDs may be related to the structure of raw materials,the synthesis conditions and the separation process.On the basis of many scholars research,this paper is based on these principles,trying different raw materials,different synthesis methods and functionalization to synthesize fluorescent probes,apply them to food detection and analysis.Specific research contents are as follows:(1)Facile synthesis of carbon nanodots with surface state-modulated fluorescence for highly sensitive and real-time detection of waterIn our study,the carbon nanodots(CDs)were synthesized by one-step solvothermal method using resorcinol as the only presusor.The obtained CDs contained abundant unsaturated oxygen-containing groups resulting from the surface oxidation.A novel,simple,and real-time fluorescent assay for the detection of water in various organic solvents was thus established by reducing the surface oxidation states.Excellent reversibility can be readily achieved by the external stimulus water and N,N0-dicyclohexylcarbodiimide(DCC).The water-induced sensitive(limit of detection ? 0.006%,v/v,in ethanol)and ultrafast(<1 s)response in emission properties was capable of water determination in spirit samples in both solution and solid-state paper test strips.(2)Aptamer induced assembly of fluorescent nitrogen-doped carbon nanodots on gold nanoclusters for high sensitive detection of OTAHere,we report a convenient and effective way to construct a ratiometric fluorescence sensor based on novel fluorescent nitrogen-doped carbon nanodots(CDs)and assembled on aptamer modified gold nanoclusters(Apta-AuNCs)for the super sensitive detection of Ochratoxin A(OTA).The prepared CDs were assembled on Apta-AuNCs by electrostatic interactions.Under the excitation wavelength of Apta-AuNCs(ex 336 nm),the fluorescence of the Apta-AuNCs(em 432 nm)was efficiently quenched while the emission of the CDs(em 533 nm)was appeared.When OTA was added to the assay solution,specific interactions between OTA and the aptamer caused release of the CDs.The fluorescence emission at 533 nm was quenched while the emission at 432 nm was recovered.the dual-emission intensity changes could be used to calculate the amount of OTA added.Thus,an obvious color change from green to blue under ultraviolet irradiation(ex 365 nm)can be observed by the naked eye.The assay exhibits super-high sensitivity with a detection limit of 8 pg/mL and a wide range of linear response of 0.01-3 ng/mL.A novel aptasensor is thus successfully constructed,it provides an efficient way for sensitive OTA sensing as well as a new technique for aptamer based novel sensor construction.(3)Carbon nanodots-assisted fluorescent detection for Melamine based on the Inner Filter Effect of Silver nanoparticlesUsing L-cysteine as carbon source material to prepare CDs has unique advantages.It not only provides carbon source,but also contains nitrogen and sulfur.The CDs emit strong fluorescence at 500 nm under 400 nm excitation,and the fluorescence quantum yield reaches 17.8%.A new assay for detection melamine(Mel)was presented based on inner filter effect(IFE)between carbon nanodots(CDs)and silver nanoparticles(AgNPs).The strategy involves two processes: the emission of CDs is quenched by AgNPs,and the addition of Mel induces AgNPs aggregation led its absorption band red shift resulting decrease IFE,thus the CDs fluorescence restored.Therefore,the enhancement of fluorescence intensity directly depends on the concentration of Mel and a fluorescent assay for Mel is developed.The strategy allows the quantitative analysis of Mel with a detection limit of 43 nM and the linear range is 0.5-30 ?M.The method based on CDs/AgNPs offers the following advantages: simplicity of design and facile preparation of nanomaterials,as well as low experimental cost,because chemical modification and separation procedures were not be needed.These results indicated that CDs have great potential for the determination in real samples.