Application Of New Fluorescent Silicon Quantum Dots In Detection Of Thiols,Tannic Acid And Cell Imaging

Silicon quantum dots refer to zero-dimensional silicon-based nanomaterials with the size closed to the exciton Bohr radius of silicon（～4.2 nm）.Silicon quantum dots usually have the advantages of wide Stokes shift,easy modification on surface,excellent biocompatibility and rich raw materials etc.Thus,silicon quantum dots exhibit great potential in the field of biochemical analysis.However,as an emerging fluorescent sensing material in recent years,the fluorescent probes based on silicon quantum dots have small number of applications in cell signal molecular detection,food additive detection and sub-organelle localization imaging.Besides,the synthesis method of long-wavelength fluorescent silicon quantum dots still needs to be improved.Herein,in order to develop the application of silicon quantum dots in the fields of disease diagnosis as well as food quality and safety controls,this thesis attempts to prepare different types of fluorescent silicon quantum dots by mild and rapid methods,and apply them to the detection of thiols,tannic acid and cell membrane localization imaging.The specific research contents are as follows:（1）Taking advantages of the good optical properties of silicon quantum dots and the redox reaction between 5,5′-dithiobis-（2-nitrobenzoic acid）（DTNB）and thiols,we developed a new detection method for thiols.The mixture of silicon quantum dots and DTNB exhibited strong blue-green emission which however was quenched within 30s of incubation with thiols.The quenching mechanism can be that DTNB was reduced to 5-thio-2-nitrobenzoic acid（TNBA）by thiols.The absorption spectrum of TNBA overlapped with the excitation and emission spectra of silicon quantum dots,so TNBA quenched the fluorescence of silicon quantum dots through inner filter effect.The method had the same linear response（3-100μM）towards three thiols including cysteine,homocysteine,and glutathione with the limits of detection between 0.80 and0.96μM.This rapid method had low cytotoxicity and excellent biocompatibility.It has been applied to the detection of thiols in serum samples and fluorescent imaging of thiols in living cells.It had great potential in thiols related biochemical analysis as well as physiological and pathological research.（2）By using dual reductants（Na HSO₃ and 4-aminophenol）and silane as reaction precursors,we synthesized a novel kind of water-soluble yellow-emitting florescent silicon quantum dots with high fluorescent quantum yields in an aqueous bath（60°C,2 h）.The effect of Na HSO₃ in reduction reagents was to avoid the over oxidation of4-aminophenol in synthesis and to improve the fluorescence quantum yield（QY=12%）of the obtained silicon quantum dots.The obtained silicon quantum dots had long emission wavelength（550 nm）,and can effectively avoid the interference of auto-absorption and spontaneous fluorescence from biomolecules.They also had strong p H tolerance（p H2-8）,great temperature stability（4-60°C）,good photostability and biocompatibility.In fluorescent imaging tests of MCF-7 cells,the yellow-emitting fluorescent silicon quantum dots were mainly distributed on the cell membrane in living cells.They had great potential in cell membrane-targeted imaging,and can be used as the cell membrane carrier of bioactive compounds.（3）Based on the yellow-emitting fluorescent silicon quantum dots prepared in previous chapter,we established a spectrofluorimetric determination method for tannic acid in water,wine and beer.In the presence of tannic acid,the amino groups on silicon quantum dots combined with the hydroxyl groups on tannic acid through electrostatic attraction.The absorbance of the formed complex was overlapped with the excitation spectrum of the silicon quantum dots,so the fluorescence of silicon quantum dots was quenched rapidly by tannic acid due to the synergistic effect of static quenching and inner filter effect.This method had a linear range from 0.2 to10.0μM with the detection limit of 50 n M.Compared with previous literatures,this method for tannic acid detection had longer emission wavelength（550 nm）,and can effectively avoid the interference of autofluorescence and background ultraviolet absorption of biological samples.This method was facile in operation,rapid in response（30 s）and highly sensitive.It has proved the good prospect of silicon quantum dots in the field of food quality and safety controls.