单个表面等离激元纳米结构调控分子光辐射的研究

Spontaneous emission of molecule or quantum dot modified by plasmonic metallic nanostructures is well known as an important and fundamental question in many interdisciplinary research fields, for instance, photovoltaic transduction, biological detection and imaging, modification of single photon source etc. In this proposal, we are planning to investigate the interaction between plasmonic nanostructure and fluorescent molecules, especially, to investigate the fluorescence behaviors near a single nanostructure, which will allow us to understand and reveal the physical origin deeply. At first, an advantaged multi-functional experimental platform will be constructed based on inverter optical microscope, single isolated nanostructure will be characterized by Atomic force microscope,scanning near-field optical microscope, confocal optical scanning image, and the surface plasmon resonance scattering spectrum can be obtained in situ. Then, fluorescence behavior in the vicinity of a single nanostructure will be investigated by single molecule fluorescence correlation spectroscopy and time-correlation single photon count technique,like as the fluorescence spectrum, intensity, lifetime, emission angular distribution and polarization properties. With the help of electromagnetic numerical simulation, single molecule behavior near single nanostructure can be obtained through statistical analysis of the experimental data. The project would lead to understand the interaction between plasmonic nanostructure and molecule deeply, and further modify or control the spontaneous emission process efficiently, then to explore the relative biological detection applications based on the understanding of the interaction.

金属纳米结构亦称光学纳米天线，其表面等离激元共振对分子自发光辐射过程的影响显著，其中的相互作用现象在许多前沿交叉领域是重要的科学问题。本项目将在实验上着重观测单个等离激元纳米结构附近的分子荧光行为，并在理论上模拟计算其相互作用过程，以深入研究和理解其物理内涵。我们将基于近场光学扫描显微镜的多功能复合测试平台，原位观测研究单个金属纳米结构附近的分子荧光光谱、荧光强度、激发态寿命、辐射远场角分布及偏振等特性。并且将把实验结果的数据统计分析和电磁数值理论模拟结果相结合，探索增强金属纳米结构与荧光分子相互作用的关键因素。期望通过选择纳米结构的材料性质，控制其几何尺寸、形状、间距等，以及设置激发和探测配置等，实现优化的纳米光学天线以调控分子荧光发射特性。使之既能够极大地增强荧光辐射强度，也能调控分子辐射方向即具有较好的单向性，实现高灵敏的单分子荧光探测，以用来探索在生物探测方面的应用研究。

对自发辐射过程的调控是许多前沿领域的重要基础科学问题，通过调节发射源附近的电磁场环境可实现对自发辐射的调制。金属纳米结构亦称光学纳米天线由于其表面等离激元共振特性，可以极大的局域增强电磁场从而可高效的调控电磁环境实现对自发辐射的调控。在项目支持下，我们首先基于近场光学扫描显微镜，建立了多功能复合测试平台，可是原位观测研究单个金属纳米结构附近的分子荧光光谱、荧光强度、激发态寿命、辐射远场角分布及偏振等特性。我们在理论上设计研究了多种光学纳米天线，如何高效增强局域激发场强，提高发射量子效率，控制发射方向，提高探测信号噪音比等多个方面。同时，在实验上我们研究了单个金属纳米结构的表面增强光谱，如表面增强石墨烯拉曼散射和金属表面增强荧光的研究。并在原位多功能探测系统上实现了单个金纳米颗粒与单个发光体的耦合，同时实现了光发射的增强和光发射方向的调控。