Preparation Of Fluorescent Carbon Nanodots And Its Application In Analytical Sensing

Carbon nanodots have been widely used in analysis detection,biological imaging,drug delivery,photocatalysis and environmental monitoring due to their unique photoluminescence properties,high photostability,low toxicity and good biocompatibility.Carbon nanodots have rich sources of precursors,diverse synthesis methods,and different physical and chemical properties.Although the emission wavelength of carbon nanodots can range from ultraviolet light to infrared light,long-wavelength carbon dots are difficult to prepare and are mostly limited to single-mode detection.In this paper,two kinds of carbon nanodots with photoluminescence properties were synthesized by hydrothermal method.Based on yellow fluorescent carbon nanodots,a multi-mode fluorescent sensing platform for detecting pH and acid-base amino acids was constructed;based on blue fluorescent carbon nanodots,a fluorescent sensing platform for detecting curcumin(Cur)was constructed.The main contents include:Chapter 1: The composition,structure and properties of carbon nanodots are briefly described.On this basis,the preparation methods,modification techniques and applications of carbon nanodots in pharmaceutical analysis were reviewed in detail.Chapter 2: Yellow fluorescent carbon nanodots(Y-CDs)were synthesized by one-pot hydrothermal method using o-phenylenediamine and paminobenzoic acid as precursors.The morphology and structure of Y-CDs were characterized by modern analytical instruments,and their properties were further analyzed.The study found that the fluorescence of Y-CDs was pHdependent.When the pH is between 2.0 and 10.0,the fluorescence intensity of Y-CDs increased with the increase of pH,and the fluorescence intensity of YCDs has an "S" relationship with pH,and the acidity coefficient p Ka is 5.14.In the range of pH 4.0 to 6.0,the fluorescence intensity of Y-CDs increases significantly with the increase of pH,and has a good linear relationship.The pH dependence of Y-CDs is mainly attributed to the protonation-deprotonation process of their surface functional groups.Based on this,a fluorescent sensor platform for detecting pH has been successfully constructed.Chapter 3: The fluorescence of Y-CDs is quenched under acidic conditions and enhanced under alkaline conditions.Amino acids are divided into acid and alkalinity.Based on this,a fluorescence sensor platform for the detection of amino acid categories has been successfully constructed.The sensing platform can qualitatively distinguish acid and basic amino acid,and quantitatively detect any of the two kinds of amino acids.Based on the low toxicity and good biocompatibility of Y-CDs,it was used for in vitro imaging of cervical cancer(He La)cells.This cell imaging experiment does not need to use nigericin to improve the permeability of cell membranes and regulate the pH balance in the cell environment.It can directly use acidic or basic amino acids to incubate cells to achieve this goal.Acid and basic amino acids directly incubate the cells,which can reduce the damage to the cells and successfully realize the detection of the amino acid types in the cells.Finally,based on YCDs,a fluorescent test strip was successfully prepared,which can qualitatively and quickly detect acid and basic amino acids.Based on the excellent physical and chemical properties of Y-CDs,the application range of Y-CDs Was further broadened.Chapter 4: Using the naturally-derived biomass(saffron)as a carbon source,blue fluorescence carbon nanodots(B-CDs)were synthesized by a onepot hydrothermal method.The morphology and structure of B-CDs were characterized by transmission electron microscope(TEM),Fourier transform infrared spectroscopy(FTIR),fluorescence spectroscopy,and ultravioletvisible absorption spectroscopy,and their performance was further analyzed.The results show that B-CDs have high water solubility,good light stability and low toxicity.Cur can significantly quench the fluorescence of B-CDs with a quenching degree of up to 84.5%.The detection of Cur by B-CDs has a wide linear range and a lower detection limit.The linear ranges are 6-20 ?M and20-50 ?M,and the corresponding minimum detection limits(LOD)are 0.184?M and 0.736 ?M,respectively.Further discussion of the mechanism found that Cur quenching of B-CDs fluorescence is attributed to the synergistic effect of internal filtration and static quenching.Based on this,a fluorescence sensor platform for Cur detection was successfully constructed.