微纳光纤谐振腔耦合的单纳米棒表面等离激元共振传感器研究

Owing to their merits such as tight confinement, localized electromagnetic field enhancement, metal nanorods have shown promising applications in high-sensitive chemical or biological sensing, and the study of metal-nanorod-mediated surface plasmon resonance (SPR) sensors has been an attractive subject in the fields of nanophotonics and optical sensing. To date, the excitation of metal nanorods mainly relies on methods such as lens focusing or prism coupling, resulting in low photon-to-plasmon conversion efficiency and large background noise. Moreover, metal nanorods usually suffer from high losses due to metal's intrinsic absorption and nanoparticles' radiative scattering, which significantly broaden the plasmonic resonance linewidths of single nanorods, and severely deteriorate the sensing sensitivity and detection limit. With this regard, we propose to realize single molecule sensors based on the coupling of single metal nanorod and micro-/nanofiber resonator. The SPR in single metal nanorods, which are deposited on the surface of optical micro-/nanofibers, can be evanescently excited with high efficiency. Based on the near-field interaction between resonant modes of micro-/nanofiber ring resonators and SPR modes of single nanorods, we will study the reduction in plasmonic resonance linewidth of single nanorods and realize label-free optical sensors with single molecule sensitivity, low noise and low power consumption. We believe that the results may be of great importance to the investigation of new mechanism and technology of SPR sensors, as well as the development of high-sensitive biological or chemical sensors in future applications such as biomedicine, environment detection and food safety.

金属纳米棒因其超强光场约束能力和局域场增强等特性在高灵敏度生物化学传感中具有潜在的应用前景，基于金属纳米棒表面等离激元共振（SPR）的传感技术已经成为纳米光子学与传感领域的前沿研究热点之一。目前金属纳米棒SPR传感器主要依靠透镜聚焦、棱镜耦合等方式激发，激发效率低、背景噪声大，且金属材料本征吸收和颗粒散射损耗使得SPR共振峰线宽较宽，限制了传感器的灵敏度和探测极限。本项目提出利用单个金属纳米棒与微纳光纤谐振腔耦合实现单分子灵敏度传感的研究设想。通过微纳光纤导模高效率耦合激发光纤表面单纳米棒SPR，利用微纳光纤环形谐振腔与金属纳米棒SPR的耦合，显著压缩SPR共振线宽，提高光谱检测分辨率，实现单分子灵敏度、无需标记、低噪声、低功耗的光学传感。研究结果对于SPR传感新机理和新技术的研究以及高灵敏度生物化学传感器在生物医学、环境检测、食品安全等方面的应用将具有重要意义。

金属纳米颗粒得益于其独特的局域表面等离激元共振特性，具有强约束、场增强等优势，在生物化学传感、表面增强拉曼光谱、纳米光子学等领域有着广泛的应用前景。然而由于辐射与非辐射损耗，金属纳米颗粒表面等离激元共振的线宽通常较宽，寿命通常很短，限制了其在生化传感等诸多领域的应用。围绕如何实现表面等离激元共振线宽的显著压缩，本项目对以下主要内容进行了深入研究：理论分析金属纳米棒与微纳光纤谐振腔近场耦合作用的机制；实验制备单个金属纳米棒与微纳光纤谐振腔的耦合结构，测量并分析了金属纳米棒局域表面等离激元共振模式与微纳光纤谐振腔谐振模式的弱耦合作用、强耦合作用、以及表面等离激元共振线宽压缩等特性；基于金属纳米颗粒-微纳光纤复合结构研究了氢气传感、湿度传感等典型应用。. 取得的重要成果、关键数据及其科学意义包括：系统建立了单个金属纳米棒与微纳光纤谐振腔近场相互作用的理论模型，从实验上实现单个金纳米棒局域表面等离激元共振与微纳光纤回音壁模式的强耦合作用，产生明显的模式劈裂和光谱线宽压缩，当光纤直径减小至1.46μm时，模式劈裂达到42.9nm，并且获得了单模、线宽仅为2nm的表面等离激元共振峰，约为非耦合单个金纳米棒散射谱线宽（约50nm）的二十五分之一，而且强度增加了30余倍，该线宽（2nm）据我们所知是目前所有文献报道的单个金纳米棒光谱中所测到的最窄线宽。在此基础上，基于金属纳米颗粒与微纳光纤耦合的复合结构实现了对单根波导弯曲损耗的显著调控，实现了探测限可达万分之五以下的高灵敏度氢气传感以及具有微米级空间分辨率的快响应分布式湿度传感等应用，在生物医学、环境检测、食品安全等方面具有潜在的应用前景。