Fabrication And Ph Sensing Application Of Sodium Yttrium Fluoride-based Fluorescent Probes

Near-infrared light-excited rare earth doped upconverting nanoparticles?UCNPs?have advantages of multi-color emission,long luminescence lifetime of hundreds of microseconds,avoiding interference to self-fluorescence interference of biomolecules,deep tissue penetration,and no photobleaching effects,showing important applications in biomedical fields such as biosensing,bioimaging and medical therapy.On the other hand,pH is one of the basic parameters for characterizing biological systems,and it is of great significance for accurate monitoring of pH values in the human body environment.In this dissertation,a novel fluorescent probe was constructed by combining Yb³⁺/Er³⁺co-doped Yttrium fluoride sodium upconversion nanomaterials?YEUNs?with rhodamine B?RHB?,and its pH sensing characteristics were studied.The main research contents of this thesis are as follows:?1?Synthesis of the YEUNs nanocrystals under high temperature pyrolysis was studied.X-ray diffractometry and transmission electron microscopy results confirmed that the YEUNs samples present hexagonal phase and spherical shape with average particle size of about 34 nm.The up-conversion luminescence properties of the YEUNs excited at 980 nm were investigated.A green emission centered at 541 nm and a red emission centered at 655 nm were identified.By adjusting the doping concentrations of rare earth ions,the 20%Yb³⁺/2%Er³⁺doped sample was revealed to present the highest emission intensity.?2?Water-soluble modification of the YEUNs was first performed using a PAA ligand exchange method,and then YEUNs@RHB fluorescent probe was fabricated.Fourier infrared spectrum confirmed that the YEUNs were coated with RHB.pH sensing properties of the was studied.It was found that the I_541/65541/655 fluorescence intensity ratio of YEUNs@RHB showed a good linear relationship with the pH values in the range of 3.0-7.0.The correlation coefficient was as high as 0.93 and the response sensitivity was 0.264/pH.In addition,the emission intensities of the YEUNs@RHB pH probe were confirmed to be constant after a long period of storage,.such pH probe was also demonstrated to have good sensing reversibility and selectivity as well as low cytotoxicity.?3?In order to further improve the sensitivity of the fluorescent probe,NaYF₄@YEUNs core-shell structures with different core/shell molar ratios were produced.The core/shell molar ratio is 1:1 resulted in formation of core-shell structured NaYF₄@YEUNs with uniform particle size and hexagonal phase.The prepared NaYF₄@YEUNs@RHB fluorescent probe not only has the advantages of good stability,low cytotoxicity,and high PH sensing reversibility and selectivity,but also has a high response sensitivity of 0.756/pH unit,which is nearly three times that of the YEUNs@RHB pH probe.This work may strongly contribute to intracellular pH detection.