Analysis And Application Based On The Fluorescence Energy Transfer Of Green Luminescent CePO₄:Tb³⁺ Nanoparticles

Fluorescence analysis method is based on certain substances to thecharacteristics of the emission fluorescence qualitative or quantitativeanalysis methods. Compared with widely applied colorimetric methodand spectrophotometric method, fluorescence analysis method has manyadvantages: good selectivity, more measurable characteristic parameters,high sensitivity, in general higher than spectrophotometric method andcolorimetry of2to3orders of magnitude. In addition, the fluorescenceanalysis method also has wide dynamic linear range, simple operation,less amount of sampling, the required equipment is simple, etc.Fluorescence analysis method as a modern analytical technology, haswidely applied in analytical chemistry and other fields. And to a certainextent, the performance of fluorescent reagent plays an important role tothe detection sensitivity and selectivity. Therefore, the preparation ofexcellent fluorescent reagent has become one focus of the fluorescenceanalysis research. Given the rare earth fluorescent nanomaterials havegood chemical stability, narrow and symmetric emission spectra, lowbiological toxicity, high resistance to photobleaching, large Stokes shifts,long fluorescence lifetime and other advantages, combined with fluorescence energy transfer principle, build some high sensitivity andgood selectivity analysis, new methods have important theoretical andapplicable value.In this paper, we used the simple and facile solvothermal method,the down-conversion green luminescent CePO4:Tb3+nanoparticles wereprepared. And based on the principle of fluorescent inner filter effect,fluorescence resonance energy transfer and energy transfer in molecules(particles), we developed some new methods for detection of biologicalsmall molecules, metal ions, etc. And applied to the analysis of syntheticsamples and actual samples. The work mainly has the following severalaspects:（1）By using facile solvothermal method, CePO4:Tb3+nanoparticleswith good luminescent performance were prepared. And characterized byTEM. Based on the inner filter effect, gold nanoparticles with highextinction coefficient as the energy receptor, we developed a turn-onfluorescent assay for the quantification determination of biologicalaminothiols. Under the optimum conditions, the linear concentrationranges were1.0×10-7-2.0×10-6M for cysteine,5.0×10-8-5.0×10-7M forglutathione and8.0×10-8-1.0×10-6M for homocysteine, respectively. Themethod is successfully applied to the quantification of biologicalaminothiols in synthetic samples.（2）Based on fluorescence resonance energy transfer (FRET) system between CePO4:Tb3+nanocrystals as donor and chromium(Ⅲ) asacceptor, we developed a rapid and easy method for quantificationaldetermination of Cr(Ⅲ). Under the optimum conditions, the linearcalibration graph was obtained (R2=0.996). The linear range and detectionlimit of chromium(Ⅲ) were0.01to2.2μmol·L-1, and9.1nmol·L-1,respectively. The proposed method had a wide linear range and wasproved to be very sensitive, rapid and simple. Moreover, the method wasapplied successfully to the determination of chromium(Ⅲ) in thesynthetic samples and tap water samples.（3）G-quadruplex-hemin complexes are DNAzyme peroxidases that canefficiently catalyze oxidation of CePO4:Tb3+nanocrystals by H2O2. In thiskind of nanoparticle, Ce3+as matrix, after absorbing the energytransferred to Tb3+, Tb3+absorbed energy then achieved5D4-7F6and5D4-7F5transition, fluorescence was achieved after returned to the groundstate. When the Ce3+oxidized to Ce4+, because of the Ce4+can not absorbthe excitation energy, the energy transfer between Ce3+and Tb3+wasdestroyed, then caused the fluorescent signal change. Since Ag+chelatesguanine bases at the binding sites are involved in G-quadruplex formation,the presence of Ag+may disrupt these structures and inhibit theperoxidase activity of G-quadruplex-hemin DNAzymes. Based on this,according to detect the fluorescent signal, we developed a turn-on methodfor quantificational determination of Ag+. The method allows a detection limit of2.05×10-7mol·L-1and a linear range of0.4~8μmol·L-1. Thecorrelation coefficient is0.995. The recovery of Ag+were measured byadding known amounts of Ag+in tap water samples, the results aresatisfying.（4） The Fenton reaction resulted in hydroxyl radicals which couldeffectively quench the fluorescence of the CePO4:Tb3+nanocrystals. Wedeveloped a new fluorescent method for determination of H2O2. At thesame time, uricase can catalyze uric acid exclusively, then producedH2O2，we can also determine the concentration of uric acid accordingly.Under the optimized conditions, we observed that the quenching of thefluorescence signal depended linearly on the H2O2concentration within arange of concentration from1×10-7mol·L-1to1×10-4mol·L-1and thedetection limit of this assay was9.3nmol·L-1. And a linear relationshipbetween uric acid concentration and CePO4:Tb3+fluorescence intensitywas obtained in the range of1×10-6mol·L-1~2.0×10-5mol·L-1uric acid(R=0.997) with the detection limit (3s/k) of0.89μM. The establishedmethod was successfully used for determination of uric acid levels inhuman plasma.