金纳米粒子单光子荧光在空间取向探测上的应用研究

Spatial orientation sensors at nanoscale are not only very important in material research, but also of great significance in understanding certain vital biological mechanisms. By exploring the origin of the single-photon luminescence from Au nanoparticles （AuNPs）via the defocused imaging of individual AuNPs, we are searching highly fluorescent AuNPs as nano-probes and developing a novel technique to detect their spatial orientations with an ordinary wide-field optical microscope. We are going to conduct research from the following three aspects: 1) Understanding the relationship between the efficiency of single-photon luminescence from AuNPs, its fluorescence spectrum and their geometric shape and size; Investigating the model to decipher defocused images of AuNPs with different shape and size; 2) Examining the polarization characteristics of the absorption dipole and emission dipole with different exciting wavelength and polarization; 3) Exploring the influence of local environment on the anisotropy of defocused images. The three main advantageous of this proposed spatial orientation sensing technique are: (1) The spatial orientation of many individual AuNPs will be able to be monitored in situ and real-time within a single frame, enabling its use as a technique for high throughput sensing. (2) The probe size will be as small as several nanometers, which is highly desirable for minimization of any potential interference from the probe itself. (3) The probe will exhibit special non-blinking and non-bleaching properties. These unique features make the orientation probes outstanding candidates for optical imaging and sensing in material science and biological applications. Moreover, the investigation on the origin of the single-photon luminescence of AuNPs will help us to understand the principle of enhancement in the emission yield of metallic nanoparticles, whereby the application fields of metallic nanoparticles in material science and biological sensing can be spread.

纳米尺度的空间取向探针不仅在材料研究中具有重要意义，在揭示某些关键的生物机理中也发挥了巨大作用。我们将以金纳米粒子作为取向探针，通过运用普通宽场显微镜对其单光子荧光进行散焦成像，从而探索其单光子荧光机理，进而提高探针的荧光强度并降低其尺寸，最终发展出一种新型的空间取向探测技术。我们将主要开展以下三个方面的研究：1）探索几何形状和尺寸对金纳米粒子荧光谱、荧光强度和散焦像模型的影响；2）研究不同激发波长和偏振下金纳米粒子吸收/辐射偶极子的偏振特性及散焦像；3）探索周围微环境对于散焦像各向异性的影响。我们这项研究所发展的空间取向探测技术将能在一帧图像中实时监测多个纳米取向探针，因此探测效率高；同时具有探针尺寸小、探针无光致闪烁和漂白现象的优势。此外,我们对于金纳米粒子单光子荧光机理的研究将有助于从物理上理解金属纳米粒子荧光加强的机制，进一步拓展其在材料研究和生物单分子传感中的应用。

纳米尺度的空间取向探针不仅在材料研究中具有重要意义，在揭示某些关键的生物机理中也发挥了巨大作用。金属纳米粒子无毒、制备简单可控，其单光子荧光稳定且量子产率高，而散焦成像技术给空间取向探测提供了平台。在本项目实施过程中我们以金纳米棒为起点，对金纳米双锥、金纳米球以及银纳米三角板的单光子荧光及其散焦像进行了系列研究，主要获得了以下研究成果：（1）基于原子力显微镜、荧光显微镜以及离散偶极近似模拟，我们提出和建立了一种测试金属纳米粒子荧光量子产率的新方法：此方法不需要使用复杂光路来探测金属纳米粒子的吸收，简单易行、高效。根据此方法我们发现，同样有效体积的金纳米双锥比金纳米棒荧光量子产率高了一倍。这项研究对于我们寻找具有高荧光强度金属纳米粒子方向探针具有重要意义；（2）通过对金纳米双锥荧光进行散焦成像以及研究不同激发偏振下散焦像和荧光光谱的变化规律，我们建立了其单光子荧光机理，探索了其在空间取向探针上应用的可能性；（3）通过对尺度介于金纳米棒和金纳米团簇的多晶金纳米球单光子荧光进行散焦成像及监测，我们提出其单光子荧光基于多偶极发射过程。作为连接纳米尺寸金纳米棒与原子尺寸金纳米团簇的纽带，金纳米球荧光机理的研究对于透彻理解金纳米粒子的荧光机理具有重要意义；（4）由于金属银虚部小，同有效体积银纳米粒子的荧光亮度比金纳米粒子高。我们研究了单个银三角板的荧光性质，发现其荧光不仅从频谱上被其所支持的表面等离子体所控制，更加重要的是，通过运用散焦成像技术以及数值模拟方法，我们发现单个银三角板的单光子荧光从空间上也由表面等离子体所控制。这项研究对于理解金属金以及银纳米粒子的单光子荧光性质具有重要意义。（5）基于数值模拟方法，我们设计了具有超高灵敏度的折射率传感器、平面手性探测器、基于磁等离子体传播的低损耗马赫-曾德干涉仪等表面等离子体器件，它们的实现对于推进集成光芯片化具有重要意义。