Exploiting Anisotropy of Plasmonic Nanostructures with Polarization Modulation Infrared Linear Dichroism Microscopy (µPM‐IRLD)

Abstract Metallic nanostructures that exhibit plasmon resonances in the mid‐infrared range are of particular interest for a variety of optical processes where the infrared excitation and/or emission can be enhanced. This plasmon‐mediated enhancement can potentially be used toward highly sensitive detection of an analyte(s) by techniques such as surface‐enhanced infrared absorption (SEIRA). To maximize the SEIRA enhancement, it is necessary to prepare highly tuned plasmonic resonances over a defined spectral range that can span over several microns. Noteworthy, nanostructures with anisotropic shapes exhibit multiple resonances that can be exploited by controlling the polarization of the input light. This study demonstrates the role of polarization‐modulation infrared linear dichroism coupled to microscopy measurements (µPM‐IRLD) as a powerful means to explore the optical properties of anisotropic nanostructures. Quantitative µPM‐IRLD measurements are conducted on a series of dendritic fractals as model structures to explore the role of structural anisotropy on the resulting surface‐enhanced infrared absorption and sensing application. Once functionalized with an analyte, the µPM‐IRLD SEIRA results highlight that it is possible to selectively enhance further vibrational modes of analytes making use of the structural anisotropy of the metallic nanostructure.