Preparation And Sensing Performance Of Nanocomposite Based On Rare Earth Upconversion Nanoparticles For Mercury Ion

Detection of metal ions is of considerable significance to environment andhuman health. Fluorescence analysis has been widely used to detection metal ions,because it offers many advantages such as high sensitivity and selectivity, specificityand versatile measurement parameters (excitation and emission spectra, intensities,intensity ratio, lifetimes). At the same time, fluorescence analysis could overcomethe large-scale analytical instruments‘shortcoming such as time consuming,expensive and complex sample pretreatment. The design and synthesis offluorescence probe is important to fluorescence analysis, a lot of organicfluorescence dyes as probes have been reported. Upconversion nanoparticles(UCNPs) that emit higher-energy visible light when excited by low-energy NIR light,offer new ideas of probe design. And UCNPs have many advantages including largeStokes shifts, good chemical and optical stability, low toxicity and noautofluorescence, it is a desired material for metal ions analysis in complex systemand biological samples. So we presented a hybrid material based on theupconversion nanoparticles and rhodamine derivatives to detect Hg2+ion. Under theexcitation of NIR light，the probe, which has near-zero autofluorescence interferenceand high penetration depth, is expected to be used for selective and sensitivequantification of Hg2+ion in environmental and biological monitoring. The major works are summaried as follows:(1) Upconversion nanoparticles NaYF4:Yb,Er were synthesized by thermaldecomposition method, and then characterized by XRD, SEM, FT-IR etc.Results showed that pure hexagonal phase nanoparticles are obtained, theparticles have uniform size and shape and the average diameter of is about40nm. FT-IR revealed that the particles bear a hydrophobic surface due tocapping of oleic acid on their surface. Under the excitation of980nm,NaYF4:Yb,Er nanoparticles demonstrated rather strong green fluorescence. Inorder to further improve the dispersibility and modificability of upconversionnanoparticles, the silica shell coating was conducted though the reversemicroemulsion method. Results demonstrated that the thickness of the silicalayer is about8nm, and after coating, the particles are water-dispersible,suitable for conjugation.(2) A novel nanocomposite sensing material was constructed by covalentlyconjugated the fluorescent probe sensitive to Hg2+ions, rhodamine Bderivative (RHO), to the modified NaYF4:Yb,Er nanoparticles. With theincrease of Hg2+concentration, the absorbance intensity of nanocomposite at550nm was enhanced gradually, and showed a good linear ship with theconcentration of Hg2+, the detection limit was3.2μΜ; while the greenupconversion fluorescence intensity was decreased, the value ofUCL540/UCL650also showed a linear ship with the concentration of Hg2+.Due to the use of near-infrared light (NIR) as excitation source, the sensor isexpected to detect Hg2+ion in complex biological or environmental samples.(3) Based on the spirolactam-ring opening system of rhodamine, we designedand synthesized rhodamine derivatives Rh1, Rh2. Absorbance andfluorescence spectrum showed that they all have certain of Hg2+sensingperformance.