Preparation Of Fluorescent Carbon Dots And Their Application In Analytical Detection And Anti-counterfeiting

In recent years,carbon dots(CDs)have aroused increasing concern as easily accessible,non-toxic and cheap fluorescent nanomaterials.The carbon dots prepared from different carbon source materials have different and abundant surface functional groups,which can provide multiple active sites and can selectively bind to various compounds,so as to construct sensitive optical sensors.In addition,the adjustability and optical stability of carbon spot photoluminescence make it an efficient anti-counterfeiting material.However,there are still some shortcomings in carbon dots,such as the relatively low fluorescence quantum yield of most carbon dots and environmental pollution caused by synthetic raw materials,which affect the practical application of carbon dots.In this paper,we try to improve the synthesis of carbon dots in green synthesis,functionalization modification and quantum yield by using biomass carbon source or functional carbon source and heteroatom doping strategy,and prepare three carbon dots with different fluorescence properties,and carry out research on their applications in fluorescence analysis detection and anti-counterfeiting.Specific contents are as follows:Chapter 1: The structure,properties,synthesis method and luminescence mechanism of CDs are briefly described,and the progress of CDs in analytical detection,fluorescence anti-counterfeiting,bioimaging and other applications are reviewed.Chapter 2: Cyan fluorescent carbon dots(N-CDs)were synthesized by a one-step hydrothermal "green" method using natural product pomegranate seeds as a carbon source mixed with ethylenediamine.The obtained N-CDs can selectively respond to p-nitrophenol(4-NP)and induce fluorescence quenching of N-CDs under the action of internal filtration effect.Based on this,a fluorescence sensing platform was constructed for the determination of 4-NP with good linearity in the concentration range of 3.0-40 μM and 70-110 μM and a detection limit of 0.413 μM,and was applied to the detection of4-NP in real water samples,showing good recovery and low relative standard deviation.N-CDs combined with filter paper/hydrogel to prepare solid sensors provide a convenient tool for detecting 4-NP in water samples.Chapter 3: Nitrogen and sulfur doped yellow-green fluorescent carbon dots(N,S-CDs)were prepared by a heteroatom doping strategy using melamine and 2-2,-dithiobenzoic acid as raw materials by a solvothermal method.N,S-CDs have a long fluorescence lifetime of 11.75 ns and excellent photostability.It was found that the interaction between curcumin and functional groups on the surface of N,S-CDs could effectively quench the fluorescence of N,S-CDs and make it have good selectivity and sensitivity for curcumin,with a detection limit of 74 n M,and the recovery of actual sample detection was 97.80 –110.30%,with a relative standard deviation(RSD,n = 6)of less than 3.In addition,the characteristics of fluorescence color change of N,S-CDs in strong acid environment were applied to information anti-counterfeiting.Chapter 4: Screening functional precursors that can rotate large conjugate structures and hydrophobic properties.Hydrophobic carbon dots(H-CDs)were synthesized by solvothermal method using 4-dianilinobenzaldehyde and urea as raw materials.It is found that carbon dots inherit the hydrophobic property of raw materials,aggregate in aqueous solution and increase fluorescence intensity,and also have photoluminescence properties in solid state.Based on this,the mechanism of luminescence may be that the protonated H-CDs aggregate under hydrophobic effect,resulting in a reduction in non-radiative leaps due to the inhibition of molecular rotation on their surface and a significant increase in fluorescence intensity.In addition,H-CDs were used for waterproof label and fingerprint detection.