Virmani Divya, Maciel-Escudero Carlos, Hillenbrand Rainer, Schnell Martin
CIC nanoGUNE BRTA, 20018, Donostia-San Sebastián, Spain.
Materials Physics Center, CSIC-UPV/EHU, 20018, Donostia-San Sebastián, Spain.
Nat Commun. 2024 Aug 8;15(1):6760. doi: 10.1038/s41467-024-50869-x.
Surface-enhanced infrared absorption (SEIRA) spectroscopy exploits the field enhancement near nanophotonic structures for highly sensitive characterization of (bio)molecules. The vibrational signature observed in SEIRA spectra is typically interpreted as field-enhanced molecular absorption. Here, we study molecular vibrations in the near field of single antennas and show that the vibrational signature can be equally well explained by field-enhanced molecular scattering. Although the infrared scattering cross section of molecules is negligible compared to their absorption cross section, the interference between the molecular-scattered field and the incident field enhances the spectral signature caused by molecular vibrational scattering by 10 orders of magnitude, thus becoming as large as that of field-enhanced molecular absorption. We provide experimental evidence that field-enhanced molecular scattering can be measured, scales in intensity with the fourth power of the local field enhancement and fully explains the vibrational signature in SEIRA spectra in both magnitude and line shape. Our work may open new paths for developing highly sensitive SEIRA sensors that exploit the presented scattering concept.
表面增强红外吸收（SEIRA）光谱利用纳米光子结构附近的场增强来对（生物）分子进行高灵敏度表征。在SEIRA光谱中观察到的振动特征通常被解释为场增强分子吸收。在此，我们研究了单个天线近场中的分子振动，并表明该振动特征同样可以通过场增强分子散射得到很好的解释。尽管与分子的吸收截面相比，其红外散射截面可忽略不计，但分子散射场与入射场之间的干涉将分子振动散射引起的光谱特征增强了10个数量级，从而变得与场增强分子吸收的光谱特征一样大。我们提供了实验证据，表明场增强分子散射可以被测量，其强度与局部场增强的四次方成正比，并且在幅度和线形上都能完全解释SEIRA光谱中的振动特征。我们的工作可能为开发利用所提出的散射概念的高灵敏度SEIRA传感器开辟新途径。
