New Fluorescent Sensors Based On Carbon Dots And Organic Small Molecules: Design,synthesis,and Application In Fluorescence Detection And Biological Imaging

Fluorescent sensors are widely used in many research fields because of their advantages such as simple use,fast response,high selectivity and sensitivity,and can provide qualitative and quantitative information.The critical topic of fluorescent sensors is fluorescent probes.With the rapid development of nanomaterials-based fluorescent probes and organic small-molecule fluorescent probes in recent years,fluorescent probes have become powerful tools in the detection of different types of analytes.However,during the development of fluorescent probes,many problems have not yet been resolved,such as:the formation process and fluorescence mechanism of carbon dots(CDs)are still controversial;the synthesis strategies of heteroatomic doping and solvent-regulated carbon dots;the application of carbon dots as a multi-purpose sensor is expanded;the development of small-molecule fluorescent probes suitable for stimulated emission depletion(STED)super-resolution imaging;the multi-mode application of STED super-resolution imaging technology,etc.Therefore,based on the design and synthesis of fluorescent sensor,this doctoral thesis studies the applications of carbon dots-based nanomaterials fluorescent probes and benzodithiophene-based organic small-molecule fluorescent probes in fluorescence sensing and biological imaging.The main research contents are as follows:1.The effects of nitrogen and sulfur doping on the performance of CDs and the multi-sensor applications of nitrogen and sulfur co-doped CDs were studied.In the first part,three CDs were synthesized using citric acid,urea and thiourea as reactants.Experimental results showed that the nitrogen doping can improve the fluorescence properties of CDs,and additional sulfur doping can improve the fluorescence stability.In addition,N-CDs showed good sensitivity and selectivity to Fe³⁺,with a detection limit of 10 n M;the N,S-CDs further expand the linear detection range of Fe³⁺.In the second part,Nitrogen and sulfur co-doped carbon dots were synthesized using methionine and ethylenediamine as precursors.N,S-CDs can be used as a very effective fluorescent sensing platform,while sensitively detecting temperature,p H and metal ions.2.Herein,we choose citric acid and melamine as the reactants,and the CDs were prepared with the same reactants by adjusting the reaction solvent to cover the entire spectral range.Both experimental and theoretical data confirm that the solvent controls the dehydration carbonization process,which affects the particle size,the graphite nitrogen content and the degree of oxidation,finally regulate the fluorescence properties of CDs.In addition,the CDs can be used as a fluorescence sensor for Fe³⁺ion detection,with a wide detection range and high sensitivity.Moreover,we used principal component analysis and Bayesian discriminant analysis to successfully design and build a food-grade sensor.The CDs fluorescence sensor can distinguish and accurately predict the varieties of jujube with good detection ability and classification accuracy.3.Herein,a sulfone-embedded distyrylbenzene derivative SO2-DSB has been reported as a novel LDs fluorescent probe suitable for STED nanoscopy imaging.This fluorescent probe exhibiting high photostability and large Stokes shift could be efficiently depleted while be not excited by the extremely strong STED lasers of 592nm or 660 nm.Consequently,STED nanoscopy imaging of LDs employed with this fluorescent probe has achieved high resolutions of 73 nm and 84 nm under 592 nm and 660 nm STED lasers,respectively.Notably,these resolutions are significantly higher than the common confocal images(resolutions of about 250 nm)and represent one of the leading results of the nanoscopy imaging of LDs so far,highlight the ability of this fluorescent probe in STED nanoscopy.In addition,the general ability of this fluorescent probe in confocal microscopy has also been demonstrated by 3D imaging and multicolor imaging.4.Herein,a benzodithiophene-tetraoxide-based molecule Lipi-BDTO has been developed that can easily undergoes the stimulated emission depletion process as well as displays high photostability.These two characters of fluorescent probe finely satisfy the requirements of STED nanoscopy imaging.Indeed,applying the probe for STED imaging achieves a high resolution of 65 nm,belonging to one of the leading results of LDs fluorescence imaging.Furthermore,the high photostability of this fluorescent probe enables to monitor the dynamics of LDs by time-lapse STED imaging as well as to visualize the three-dimensional(3D)spatial distribution of LDs by 3D STED imaging.Notably,the resolution of 3D STED image represents one of the best LDs fluorescence imaging results so far.Besides of STED nanoscopy imaging,the superior utility of this fluorescent probe has been also demonstrated in two-color 3D confocal imaging and four-color confocal imaging.