Synthesis And Applications Of NIR-Stimulated Electron-Trapping Upconversion Luminescence Nanoparticles

Fluorescence technology has become an important tool for analyzing manyphysical,chemical and biological processes.Currently,fluorescent materials such as quantum dots,organic fluorescent proteins,and metal nanoclusters have been designed and developed to meet the needs of various applications.Among them,rare-earth doped alkaline earth sulfides have received mor e and more attention due to their special electron-trapping photostimulated luminescence mechanism.At present,the synthesized rare-earth doped alkaline earth sulfides are mostly bulk phosphors with relatively large particle size and easily hydrolyzed in an aqueous solution or even in a humid air to lose the original advantages.Therefore,it is still a difficult task to develop and design a more ideal preparation method and modification process to meet the applications of more fields.In this paper,a nov el reverse microemulsion strategy was used to synthesize nanometer-sized rare-earth doped alkaline earth sulfides,which were functionally modified and applied to NADH detection and latent fingerprint imaging.It mainly includes the following research cont ents:1.Preparation and modification of electron-trapping upconversion lumin-escence nanoparticles with CaS as matrixThe rare-earth doped alkaline earth sulfide has higher fluorescence quantum conversion efficiency than the existing upconversion luminescent materials due to its special electron-trapping photostimulated luminescence mechanism.In this paper,the upconversion nanoparticles doped with Eu²⁺/Sm³⁺/Mn³⁺were prepared by a reverse microemulsion method.It has a average particle size of about 30 nm a nd a relatively regular spherical structure,a narrow particle size distribution and a face-centered cubic crystal which is consistent with the pure phase CaS crystal.Under excitation of980 nm near-infrared light,the sample has a very strong red upconversion fluorescence emission near 645 nm.The luminescence intensity is significantly enhanced compared to the conventional NaYF₄ UCNPs.Finally,surface modification of CaS:Eu/Sm/Mn UCNPs with 1-Dodecanethiol?DT?and 11-mercaptoundecanoic acid?MUA?provides higher water solubility,single dispersibility and biocompatibility so that it can be better used in biological analysis.2.Quantitative detection of NADH by back-titration fluorescence analysis based on CaS:Eu/Sm/Mn@DT/MUA-NB_X UCNPsIn this chapter,an upconversion fluorescence sensing system for quantitative detection of NADH content was designed based on the back-titration strategy:CaS:Eu/Sm/Mn@DT/MUA UCNPs were mixed into NB-NADH reaction system to obtain CaS:Eu/Sm/Mn@DT/MUA-NBx UCNPs.Since there is an effective spectral overlap between the emission spectrum of UCNPs and the absorption spectrum of NB molecules,the FRET effect was generated under excitation of 980 nm near-infrared light.According to the remaining of unreacted NB molecules in the NB-NADH reaction solution,the different loading was induced,which caused different upconversion fluorescence responses of CaS:Eu/Sm/Mn@DT/MUA-NBx UCNPs at645 nm.Therefore,indirect quantitative analysis of NADH was achieved.The fluorescence sensing system exhibited a good linear relationship in the range of NADH concentration of 0-200?M,and the correlation coefficient R²=0.996,the detection limit LOD=1.125?M.In addition,the sensing system was applied to quantify the NADH weight in dietary supplements to examine its ability to analyze actual samples.The calculated results showed that the NADH weight in each tablet was close to 5 mg of the commercial marker.The recoveries were 98%¹02%and RSD below 5.0%.3.Application of CaS:Eu/Sm/Mn@DT/MUA-Arg UCNPs in latent fingerprint imagingIn this chapter,arginine was designed as a targeting ligand for residual amino acids in latent fingerprints,and arginine-modified upconversion luminescence nanoparticles CaS:Eu/Sm/Mn@DT/MUA-Arg UCNPs were synthesized.It was applied to the latent fingerprint imaging on different substrates including glass,foil,tile and plastic.Under the excitation of 980 nm near-infrared light,the fingerprint fluorescence image was captured by an ordinary smartphone which has the advantages of smooth and clear fingerprint ridges,high imaging contrast and low background fluorescence.