Institut Fresnel, Aix-Marseille Université, CNRS, Ecole Centrale Marseille, Campus de St Jérôme, 13397 Marseille, France.
Nano Lett. 2011 Jun 8;11(6):2400-6. doi: 10.1021/nl200772d. Epub 2011 May 18.
Spontaneous emission of fluorescent molecules or quantum dots is radiated along all directions when emitters are diluted in a liquid solution, which severely limits the amount of collected light. Besides, the emission direction does not carry any useful information and cannot be used to sort different molecules. To go beyond these limits, optical antennas have been recently introduced as conceptual tools to control the radiation properties for nanoemitters fixed on a substrate. Despite intense recent research, controlling the luminescence directivity remains a challenge for emitters with random positions and orientations, which is a key for several biomolecular screening applications. Here, we present full directional control of the fluorescence emission from molecules in water solution by an optical antenna made of a nanoaperture surrounded by a periodic set of shallow grooves in a gold film. For each emission wavelength, the fluorescence beam can be directed along a specific direction with a given angular width, hereby realizing a micrometer-size dispersive antenna. We demonstrate the fluorescence beaming results from an interference phenomenon and provide physical optics guidelines to control the fluorescence directivity by tuning the groove-nanoaperture distance. This photon-sorting capability provides a new approach for high-sensitivity screening of molecular species in solution.
当荧光分子或量子点在液体溶液中稀释时，自发发射的光会沿各个方向辐射，这严重限制了收集到的光的数量。此外，发射方向不携带任何有用信息，也不能用于对不同分子进行分类。为了克服这些限制，光学天线最近被引入作为控制固定在基底上的纳米发射器的辐射特性的概念工具。尽管最近进行了大量研究，但对于具有随机位置和取向的发射器来说，控制发光方向性仍然是一个挑战，这是许多生物分子筛选应用的关键。在这里，我们通过由金膜中的纳米孔周围周期性浅槽组成的光学天线，实现了水溶液中分子荧光发射的全方向控制。对于每个发射波长，可以将荧光束沿特定方向以给定的角度宽度引导，从而实现了具有微米尺寸的色散天线。我们从干涉现象证明了荧光定向结果，并提供了物理光学指南，通过调整槽-纳米孔距离来控制荧光方向性。这种光子分选能力为溶液中分子种类的高灵敏度筛选提供了一种新方法。
