以NaYF4为代表的上转换纳米晶作为细胞及组织标记的研究越来越热。 但易团聚,水溶性、生物兼容性差,没有与生物偶联官能团等缺点限制了其应用,因而表面修饰显得尤为重要。 作者通过水热和共沉淀相结合方法,制备了NaYF4:Yb3+,Er3+上转换纳米晶,并对其包覆二氧化硅壳层。 SEM表征硅包覆前后分别为25和250 nm的单分散粒子,说明硅已成功地包覆于纳米晶表面。 980 nm激光照射下,样品的PBS胶体溶液呈可视上转换绿光。 上转换荧光光谱和寿命均表明二氧化硅壳层对其发光性质影响很小。 圆二色谱说明蛋白分子通过戊二醛与纳米晶偶联前后的二级结构基本不变。 基于硅片上的抗原抗体荧光免疫识别试验进一步验证了偶联蛋白分子的特异性,表明该上转换纳米晶适合于生物标记。

The authors synthesized a kind of upconversion nanocrystals NaYF4:Yb3+,Er3+ via the hydrothermal assisted homogeneous precipitation method,and then the nanocrystal was coated with silica. The SEM image demonstrated that the as-prepared samples were uniform in size distribution with ca. 25 nm before and ca. 250 nm after silica coating,respectively. The upconversion spectra and photoluminescence lifetime measurement showed that the silica shell had hardly effect on the properties of fluorescence of the NaYF4:Yb3+,Er3+ nanocrystals. At the same time,the naked eye-visible green upconversion fluorescence pattern was acquired from the as-prepared upconversion nanoparticles in the PBS buffer (2 wt%) excited by 980 nm laser at room temperature. These water-soluble nanoparticles were linked to the antibodies using the coupling reagents glutaraldehyde. The circular dichroism (CD) spectra of antibody and upconversion nanoparticles-antibody conjugates were very similar to each other,indicating that the secondary structure of antibody remained largely intact after the conjugation. Finally,antigen-antibody recognition reaction was performed on the surface of a silicon slide. The immunofluorescence in vitro indicated that the upconversion nanoparticles-antibody bioconjugates had excellent species-specific detection ability with hardly non-specific binding. Based on the present results,it is anticipated that the silica-coated upconversion nanoparticles are suitable for use as biolabeling materials.