| Rare earth co-doped upconversion nanoparticles (UCNPs), which can convert a radiation from a longer wavelength to a shorter wavelength, have great potential uses in bio-imaging and biomedical detection. Hexagonal sodium yttrium fluoride (NaYF4:Yb,Er) is one of the most efficient UCNPs. However, UCNPs with good properties are often obtained from oil-phase or from sintering at a high temperature after precipitation from aqueous solution. The as-prepared nanocrystals tend to precipitate in distilled water due to the lack of hydrophilic chemical groups on their surfaces, limiting their biomedical application. Therefore, it is necessary to carry out the surface modification of NaYF4. In this paper, NaYF4:Yb,Er/NaYF4 nanoparticles (NPs) were obtained in an oil phase at a low temperature firstly, and compared with NaYF4:Yb,Er NPs, the obtained NaYF4:Yb,Er/NaYF4NPs displayed a high luminescent intensity with favorable crystal phase. Then, water-soluble polymer polyacrylamide (PAM) was used to modify the NaYF4:Yb,Er/NaYF4 NPs by in-situ polymerization. After that, superparamagnetic magnetite oxide nanoparticles (Fe3O4 NPs) were synthesized through coprecipitation method; the as-prepared Fe3O>4 NPs were modified by polyacrylamide (PAM) to improve surface properties. At last, NaYF4:Yb,Er/NaYF4/PAM and FeO4/PAM NPs were conjugated with the AFP antibodies through covalent binding respectively, which were used in alpha-fetoprotein (AFP) detection of clinic blood. The details are showed in the following parts.Firstly, an oil-water interface method was used to prepared well-dispersed hexagonal NaYF4:Yb,Er and NaYF4:Yb,Er/NaYF4 NPs at a temperature of 40℃, in-situ polymerization was developed to coat PAM on the surface of the NPs afterwards. The resulting UCNPs and the PAM coated nanocomposites were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and upconversion photoluminescence spectroscopy (PL). The results indicated that the as-prepared NaYF4:Yb,Er/NaYF4 NPs exhibited a pure β-NaYF4 phase with a mean size of 12.0 nm. Compared with NaYF4:Yb,Er NPs, NaYF4:Yb,Er/NaYF4 NPs showed higher luminescence intensity and a bigger size. RAM coated NaYF4:Yb,Er/NaYF4 NPs displayed a size of 110 nm with good micro-morphology, and a slight decline luminescent intensity.Secondly, superparamagnetic magnetite oxide nanoparticles (Fe3O4 NPs) with a size of 11.1 nm were synthesized through coprecipitation method. Then the Fe3O4 NPs were coated with PAM by in-situ polymerization to obtain Fe3O4/PAM nanocomposites, which showed an obvious core-shell structure. XRD, TEM, FT-IR, TGA and Vibrating Sample Magnetometer (VSM) were used to characterize the as-obtained NPs. The results demonstrated the Fe3O4/PAM NPs having preferably micromorphology and a mean size of 70 nm with strong magnetism were obtained at 0℃ with the ratio of [Fe3O4 nanopowder]/[PAM] was 60 within 2.5 h.Finally, NaYF4:Yb,Er/NaYF4/PAM nanocomposites and IgG antibody, Fe3O4/PAM nanocomposites and IgG antibody were mixed and stirred overnight to conjugate by covalent binding respectively. For the detection of the AFP antigen in human serum, the calibration curve and the working equation are crucial. The processes were:(1) The Fe3O4/PAM nanocomposites were obtained and conjugated with mouse IgG antibody (the primary antibody). Then the complexes of primary antibody and magnetic nanoparticles were used to capture the AFP antigen. (2) The water-soluble fluorescent NaYF4 nanocomposites were synthesized and conjugated with mouse IgG antibody (the second antibody). (3) The sandwich immunoreaction occurred, and metered the solution volume to 1 mL with PL test. The relationship between PL intensity of the complex and the concentration of AFP was determined, and the calibration equation, y=0.2128x +14.5009 (x:AFP antigen, y:PL intensity) was obtained with a linear correlation coefficient of 0.99735. (4) The human serum samples of 20 people were tested. The result showed that the outcomes determined by this method were similar to those determined by Roche chemiluminescence method. The slight difference still existed and the reason may lie in that the specificity of the antigen is not strong enough. |
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