Ultra-sensitive vibrational spectroscopy of protein monolayers with plasmonic nanoantenna arrays
Ultra-sensitive vibrational spectroscopy of protein monolayers with plasmonic nanoantenna arrays
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DOI：
10.1073/pnas.0907459106
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发表时间：
2009-11-17
影响因子：
11.1
通讯作者：
Altug, Hatice
中科院分区：
文献类型：
--
作者：
Adato, Ronen;Yanik, Ahmet A.;Altug, Hatice
红外吸收光谱能够直接获取分子结构的振动指纹，是生物分子功能研究的有力方法。尽管蛋白质红外活性模式的固有吸收截面比相应的拉曼截面大近 10 个数量级，但与基于荧光标记的方法相比，它们仍然很小。在这里，我们开发了一种基于等离子体纳米天线阵列集体激发的新工具，并演示了对单个蛋白质单层振动特征的直接检测。我们首先定制单个纳米天线的几何形状，以形成与分子振动模式匹配的共振结构。然后，定制的纳米天线的排列方式使得它们的同相偶极耦合导致具有强烈增强的近场的整体的集体激发。天线阵列的组合集体和个体等离子体响应在获得 10(4)-10(5) 的信号增强因子方面发挥着关键作用。我们实现了整个阵列 zeptomole 水平上蛋白质振动光谱的测量，相当于每个天线仅 145 个分子。通过逐渐加载具有不同蛋白质膜厚度的纳米天线，证明了吸收信号的等离子体增强的近场性质。最后，介绍了一种基于非平衡格林函数形式的高级模型，该模型解释了观察到的法诺型吸收线形状以及吸收强度随天线谐振的调整。
Infrared absorption spectroscopy enabling direct access to vibrational fingerprints of the molecular structure is a powerful method for functional studies of bio-molecules. Although the intrinsic absorption cross-sections of IR active modes of proteins are nearly 10 orders of magnitude larger than the corresponding Raman cross-sections, they are still small compared to that of fluorescence-label based methods. Here, we developed a new tool based on collective excitation of plasmonic nanoantenna arrays and demonstrated direct detection of vibrational signatures of single protein monolayers. We first tailored the geometry of individual nanoantennas to form resonant structures that match the molecular vibrational modes. The tailored nanoantennas are then arranged in such a way that their in-phase dipolar coupling leads to a collective excitation of the ensemble with strongly enhanced near fields. The combined collective and individual plasmonic responses of the antenna array play a critical role in attaining signal enhancement factors of 10(4)-10(5). We achieved measurement of the vibrational spectra of proteins at zeptomole levels for the entire array, corresponding to only 145 molecules per antenna. The near-field nature of the plasmonic enhancement of the absorption signals is demonstrated with progressive loading of the nanoantennas with varying protein film thicknesses. Finally, an advanced model based on nonequilibrium Green's function formalism is introduced, which explains the observed Fano-type absorption line-shapes and tuning of the absorption strengths with the antenna resonance.