Preparation And Application Of Alkaline Earth Sulfide Nanoparticles Based Electron Trapping-Near Infrared Stimulated Luminescence

Fluorescence is a common natural phenomenon and it is widely used in sensitive analysis and biolabeling due to its high sensitivity.This thesis focuses on the up-convered fluorescence of rare earth doped alkaline earth sulfide under near infrared light?NIR?excitation.After optimization of reaction conditions,alkaline earth sulfide nanomaterials?AES NPs?with excellent optical properties are successfully obtained,the AES NPs emit intense fluorescence under 980 nm near infrared light illumination,so as to break through the shortage of insufficient fluorescence brightness of traditional rare earth doped inorganic upconversion fluorescent materials.Correspondingly,applications have been carried out for fluorescence detection,chemical sensing,biolabeling and imaging.Electron-trapping materials?ETM?are a large class of metal ions doped inorganic crystalline that capture excited-state electrons,store energy and emit trapped electrons with a shorter wavelength when excited by a suitable wavelength of light.Notably,the rare-earth ions doped alkaline earth metal sulfides?AES?are representative,due to its excellent NIR-visible conversion capability.The bottlenecks of traditional uponcersion luminescence materials,like insufficient up-conversion fluorescence intensity,can be overcame by introduction of the highly fluorescent AES NPs.However,there are many defects in AES materials at present,such as poor chemical stability,large particle size,low dispersion,and fixed fluorescent emission peak,which seriously limit its further applications.Aiming at the defects,relevant research work was carries out to make it possible to become a new type of NIR stimulated fluorescent nanomaterials.Specific contents are as follows:Given the shortcoming of CaS or SrS-based electron-trapping materials,including large particle size,which were obtained by the existing preparation methods.We proposed a approach of AES nanomaterials preparation based on the inverse microemulsion method,and obtained AES NPs were uniform in size and less than 100nm.The fluorescence intensity of the prepared AES NPs was greatly enhanced by optimizing the preparation conditions?concentration of doping ions,reaction temperature,etc.?.In addition,we found that the emission peak of AES NPs could be shifted when different rare earth ions were doped,which acted as luminescent centers,thereby realizing the different wavelength fluorescence emission of AES NPs under the same 980 nm near infrared light irradiation.The as-prepared AES NPs were of low chemical stability in aqueous solution due to the sulfide matrix itself,so we modified the prepared AES NPs with the amphiphilic organic ligand dodecanethiol?DT?and mercaptoundecanoic acid?MUA?.The modified AES NPs were able to dispersed in water homogeneously,meanwhile it kept good chemical stability in aqueous solution.Most importantly,the fluorescence emission can be maintained strongly,and the surface of the nanoparticles were rich in carboxyl functional groups,which made it especially suitable for functional molecules modification.Thus the DT/MUA encapsulated AES NPs were adequate to used as a class of highly efficient water-soluble fluorescent nanomaterials.On the basis of obtained multicolor AES NPs with high brightness,strong stability and good water solubility,we applied the AES NPs to fluorescence detection,LED devices,information coding and other applications stimulated by 980 nm near infrared light,similar to traditional inorganic upconversion fluorescent nanomaterials,the AESNPs also showed very low background signal interference in corresponding applications,especially in the cell and animal imaging,intense fluorescence under 980nm near infrared light excitation enabled deeper imaging depth,it was very conducive to fluorescence imaging of deep tissue and organs.Compared with traditional rare earth doped NaYF₄ upconversion fluorescent nanomaterials,the AES NPs have much higher signal-to-noise ratio and better imaging effect.Up-converted fluorescence based strip sensing can effectively avoid the interference of background fluorescence resulted from sample matrix,but the traditional upconversion fluorescence nanomaterials are not sufficiently luminous under 980 nm laser irradiation,which is not adequate to high sensitivity detection.Therefore,bright CaS:Eu,Sm,Mn nanomaterials were used as fluorescent donors based on the principle of fluorescence resonance energy transfer?FRET?.We integrated a small power 980 nm laser and smart phone into a portable device to achieve visualized determination of sulfite in food sample.Benefited from advantages of up-converted fluorescence,the interference of matrix could be largely reduced,so the sample pre-treatment process was no longer necessary in the test paper detection,this really resulted in rapid and on-site food detection.Considering the merits of AES NPs in bioimaging,we modified different target recognition molecules with two different fluorescence emissive AES NPs to achieve specific binding for Gram-positive bacteria and Gram-negative bacteria,respectively.Bacteria could be fluorescently imaged and directly classified through different fluorescent color.The in vivo experiment also proved that AES NPs could specifically label the bacterial infections with good discrimination.Similarly,bacteria in the infectious sites could be classified based on the fluorescence wavelengths differentiation.Significantly the bacteria detection on the living tissue was of high sensitivity and deep depth because of the up-converted fluorescence imaging mode.This work opened a new perspective for early and deep tissue infection detection.In this thesis,we have prepared,developed and applied a battery of AES NPs which were excited by near-infrared light?980nm?,such the AES NPs had advantages of low background interference,high signal-to-noise ratio and high penetration depth.We have explored the nanoparticles in ultra-sensitive fingerprint detection,fluorescent information coding.At the same time,the sulfite test strip using AES NPs was studied,fast and in-field detection ability in complex matrix samples was proved.Sigificantly,the AES NPs showed extraordinary superiority in bio-imaging applications,like cell fluorescent labeling and in vivo organs fluorescent imaging.Highly fluorescent AES NPs enabled strong fluorescence signal thus realizing the sensitive bacteria detection and differentiation on the living level.These work provided a new kind of 980 nm near-infrared light irradiated fluorescent nano-materials,and proposed a new idea for up-converted fluorescence detection and in vivo imaging.