Probing the electromagnetic field of a 15-nanometre hotspot by single molecule imaging
Probing the electromagnetic field of a 15-nanometre hotspot by single molecule imaging
复制标题
通过单分子成像探测 15 纳米热点的电磁场
DOI：
10.1038/nature09698
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发表时间：
2011-01-20
期刊：
影响因子：
64.8
通讯作者：
Zhang, Xiang
中科院分区：
文献类型：
--
作者：
Cang, Hu;Labno, Anna;Zhang, Xiang
当光线照射粗糙的金属表面时，会出现热点，光线集中在纳米尺度上，产生强烈的电磁场。这种现象被称为表面增强效应，具有广泛的潜在应用，例如微弱化学信号的检测。热点被认为与局部电磁模式有关，由表面纹理的随机性引起。探测热点的电磁场将为揭示产生增强的机制提供更多的见解;然而，它需要1-2 nm的空间分辨率，这一直是光学领域的一个长期挑战。光学显微镜的分辨率被限制在入射光波长的大约一半，大约200-300 nm。虽然目前最先进的技术，包括近场扫描光学显微镜，电子能量损失光谱，阴极发光成像和双光子光电发射成像具有亚波长分辨率，它们要么引入不可忽略的扰动量，使数据的解释复杂化，要么仅在真空中操作。因此，在发现表面增强效应30多年之后，局部场如何分布仍然是未知的。在这里，我们提出了一种技术，利用布朗运动的单分子探测本地字段。它能够对铝薄膜和银纳米颗粒簇表面上的单个热点的荧光增强分布进行二维成像，精度低至1.2 nm。在这两个系统中观察到强烈的荧光增强，分别高达54和136倍。这种强烈的增强表明，从热点的峰值指数衰减的局部场主导荧光增强曲线。
When light illuminates a rough metallic surface, hotspots can appear, where the light is concentrated on the nanometre scale, producing an intense electromagnetic field. This phenomenon, called the surface enhancement effect,, has a broad range of potential applications, such as the detection of weak chemical signals. Hotspots are believed to be associated with localized electromagnetic modes,, caused by the randomness of the surface texture. Probing the electromagnetic field of the hotspots would offer much insight towards uncovering the mechanism generating the enhancement; however, it requires a spatial resolution of 1–2 nm, which has been a long-standing challenge in optics. The resolution of an optical microscope is limited to about half the wavelength of the incident light, approximately 200–300 nm. Although current state-of-the-art techniques, including near-field scanning optical microscopy, electron energy-loss spectroscopy, cathode luminescence imaging and two-photon photoemission imaging have subwavelength resolution, they either introduce a non-negligible amount of perturbation, complicating interpretation of the data, or operate only in a vacuum. As a result, after more than 30 years since the discovery of the surface enhancement effect,,, how the local field is distributed remains unknown. Here we present a technique that uses Brownian motion of single molecules to probe the local field. It enables two-dimensional imaging of the fluorescence enhancement profile of single hotspots on the surfaces of aluminium thin films and silver nanoparticle clusters, with accuracy down to 1.2 nm. Strong fluorescence enhancements, up to 54 and 136 times respectively, are observed in those two systems. This strong enhancement indicates that the local field, which decays exponentially from the peak of a hotspot, dominates the fluorescence enhancement profile.