Design And Synthesis Of Ratio Probe Based On Carbon Dots And Application In Detection

Carbon dots have attracted much attention as zero-dimensional carbon-based nanomaterials because of their unique properties.The carbon dot s has unique optical properties such as stable fluorescent signal,no light flicker,adjustable excitation and emission wavelengths,and physical and chemical properties such as small size effect,huge specific surface area,and extremely high reactivity.It is designed as a fluorescent probe for analysis and detection of metal ions,small molecular substances,biological macromolecules,etc.As a fluorescent probe,carbon dots have the advantages of simple and fast operation,high sensitivity,good selectivity,and have been widely developed and utilized.With the continuous development of carbon dots,the detection of a single fluorescent signal is not enough to meet the needs of scientific research,so ratio probes based on carbon dots came into being.Because the change of the characteristic emission peak at different wavelengths will cause the corresponding change of the color,it has attracted much attention in visual detection,cell imaging,biomedicine,etc.The ratio probe can effectively eliminate background interference and condition fluctuations,and is more reliable than single signal detection.Based on the carbon dots,three ratio probes were designed and applied to the analysis and detection of tryptophan,Fe（III）,folic acid and tetracycline.The main research contents are as follows:1.Design of fluorescence and second-order light scattering ratio probes for Cu-CDs and application to the detection of tryptophan and Fe（III）.In this study,copper-doped carbon dots（Cu-CDs）were synthesized by a simple calcination and pyrolysis method using copper disodium edetate and ascorbic acid as precursors.Under a single excitation at 308 nm,Cu-CDs will generate two response signals corresponding to the fluorescence characteristic peak at 396 nm and the second-order light scattering peak at 617 nm.The design of the ratio probe is realized.Tryptophan as the detection target of the fluorescence characteristic peak response,due to the synergistic effect of hydrogen bonding,the fluorescence characteristic peak of Cu-CDs will be enhanced while the second-order light scattering peak will not change.Fe（III）as the detection target for the response of the second-order light scattering peak,the second-order light scattering peak of Cu-CDs is enhanced and the fluorescence characteristic peak is unchanged due to the mechanism of"OFF"of photoinduced electron transfer.The linear response ranges are 0.5-250μmol/L and 0.1-50μmol/L,respectively.Compared with other analytes,the sensing system showed good selectivity and sensitivity for tryptophan and Fe（III）,with detection limits as low as 275 nmol/L and 46 nmol/L,respectively.In addition,the proposed sensing system shows good application prospects for the quantitative determination of tryptophan and Fe（III）in actual samples.2.Design of N,S,I-CDs as ratio probes and their application in the detection of folic acid.In this study,a one-step hydrothermal method using thiocyanate as the carbon and sulfur sources,potassium iodate as the iodine source,and ethylenediamine as the nitrogen source successfully synthesized nitrogen,sulfur,and iodine co-doped carbon spots（N,S,I-CDs）.N,S,I-CDs showed bright blue fluorescence under ultraviolet light irradiation,and the fluorescence quantum yield was as high as 32.4%.Under a single excitation,N,S,I-CDs will have a single fluorescence emission peak at 388nm.When folic acid is added,N,S,I-CDs and folic acid are tightly bound together under the action of hydrogen bonding,and it occurs.Fluorescence resonance energy transfer effect makes the characteristic emission peak at 388 nm quench obviously.At the same time,a new fluorescence emission peak appears at 458 nm and shows an increasing trend.Two fluorescence emission peaks appear at the same time.Therefore,a sensitive detection of folic acid was achieved with the ratio of I₄₅₈/I₃₈₈.The linear range of folic acid detection is 0.1-175μmol/L,the detection limit is 84 nmol/L,and the color change caused by the change in the peak fluorescence emission of the ratio probe is successfully applied to the imaging study of human osteosarcoma cells,which provided a new tool for the detection of folate in the cells.3.Design of SiCDs and RhB construction ratio probe and its application in detection of tetracycline.In this study,silicon-doped carbon dots（Si-CDs）were synthesized by one-step hydrothermal method using phenylboronic acid and 3-aminopropyltriethoxysilane as precursors.SiCDs have strong blue fluorescence with a fluorescence yield of 17.2%.SiCDs will have an emission peak at 414 nm when the excitation wavelength is 324 nm.In order to construct the ratio probe,Rhodamine B（Rh B）was introduced as another fluorescence signal.When the excitation wavelength is 324 nm,Rh B will have a characteristic emission peak at 578 nm,the characteristic emission peak of the position is different from the SiCDs to realize the construction of the ratio probe（SiCDs-Rh B）.As a detection target,tetracycline will have a fluorescence resonance energy transfer effect with SiCDs and quench the emission peak at 414 nm.In addition,the characteristic emission peak of Rh B at 578 nm will not change because Rh B does not interact with tetracycline.In this way,a ratio detection system was established.SiCDs-Rh B has good selectivity and sensitivity for the detection of tetracycline,with a linear range of 0.1-100μmol/L and a detection limit of 83 nmol/L.In addition,the application of this probe to the detection of tetracycline in meat has shown good development prospects.