中空夹心结构上转换荧光材料的设计、合成及FRET应用

The NIR-excitation and anti-Stokes emission of upconversion phosphors (UCP) has endowed the material with promising prospect as the energy donor for fluorescence resonance energy transfer (FRET). Because of its strong ability to eliminate the direct excitation of energy acceptor, so as to enhance the signal-to-background ratio and to avoid false positive results, the upconversion (UC)-FRET technique has gained extensive and increasing attention recently. Nevertheless, the relatively low energy-transfer efficiency of UCP is the key limitation for the sensitivity of this analytical technique, which is due to the high dependence of FRET efficiency on the donor-to-acceptor distance and the fact that UCP normally possesses rather large size. Besides, the unsatisfying dispersibility of UCP in aqueous solutions is another concern that restricts its application. To meet these challenges, we hereby propose the idea of hollow sandwich-structure UCP in this project. The sandwich design is to locate the emitting ions near the surface of nanoparticles, so that they are within the effective FRET distance and the FRET efficiency can be thus enhanced. In another hand, the hollow structure is to decrease the density of UCP so as to reduce its sedimentation rate and improve the stability of UCP solution. The design is novel and original, through which the bottleneck of the methodology of UC-FRET is expected to be well resolved, and also, the analytical application of upconversion phosphors can be considerably facilitated.

摘要：近红外激发、反斯托克斯发射的上转换荧光纳米材料（UCP）是一类潜在的性能优异的荧光共振能量转移（FRET）供体。它可完全消除能量受体的直接激发，降低FRET分析的背景和假阳性结果的几率。然而，由于FRET效率对供、受体距离的高度依赖以及目前UCP尺寸偏大的现实，UCP的能量转移效率低已成为UC-FRET灵敏度提升的关键障碍；此外，UCP水溶液分散性欠佳是限制其分析应用的另一个重要因素。为克服上转换荧光分析的缺陷，本课题提出"中空夹心结构上转换荧光材料"的设计思想。通过夹心结构设计将发光中心离子定位于纳米材料表面，使其处在有效的能量转移距离从而提高FRET效率；中空结构的设计旨在大幅减小UCP材料密度及其重力沉降，增加其水溶液分散性和稳定性。本课题思想具有原始创新性，通过此项研究有望获得一类全新的UCP材料，突破上转换荧光共振能量转移的方法学瓶颈，促进上转换荧光的分析应用。

本项目旨在通过改造上转换荧光纳米材料自身结构，突破上转换荧光共振能量转移方法学瓶颈，促进上转换荧光的分析应用。围绕这一目标，本项目执行期间通过夹心结构的设计将发光中心离子定位于纳米材料表面附近，使其处在有效的能量转移距离从而提高FRET效率。以有机小分子染料、贵金属纳米簇及重金属离子等材料作为能量受体，构建了一系列上转换荧光纳米探针，用于细胞内活性物质的成像分析；发展了以MnO2、WS2等二维平面共价晶体为能量受体的上转换FRET分析平台；设计了一系列双光子激发的荧光探针用于体内成像分析。通过改进能量受体及改造上转换荧光纳米材料自身的结构，不断提高上转换FRET分析的能量转移效率及体系的生物相容性，从而提升方法的灵敏度。将所构建的探针应用于细胞及组织的生物成像，能够实现对体内多种活性物质的检测，并获得较高的灵敏度和稳定性，充分证实了上转换荧光分析方法在生物医学分析中的优良应用前景。与此同时，以双光子激发分子为荧光团，结合多种目标识别域，发展了一系列双光子荧光分子探针，实现细胞、组织样品中目标物监测。在JACS、Angew. Chem.等期刊发表论文23篇。本项目主要创新性成果包括：.1）以二维平面共价晶体（MnO2、WS2）等作为能量受体，提高了FRET效率。.2）提出以银纳米簇作为上转换荧光纳米材料的能量受体，在提高FRET效率的同时，兼顾体系的生物相容性及稳定性。.3）开创性地提出夹层结构上转换纳米材料，从源头突破上转换荧光共振能量转移方法的瓶颈。.4）以重金属离子作为上转换荧光纳米材料的猝灭剂，打破FRET方法中对光谱匹配的依赖性。.5）发展了双机理检测的双光子荧光探针，提高探针灵敏度。.6）构建了红光发射的双光子荧光探针，从而有效提高荧光成像的穿透深度。