Resonant Coupling between Molecular Vibrations and Localized Surface Plasmon Resonance of Faceted Metal Oxide Nanocrystals

Abstract

Doped metal oxides are plasmonic materials that boast both synthetic and postsynthetic spectral tunability. They have already enabled promising smart window and optoelectronic technologies and have been proposed for use in surface enhanced infrared absorption spectroscopy (SEIRA) and sensing applications. Herein, we report the first step toward realization of the former utilizing cubic F and Sn codoped InO nanocrystals (NCs) to couple to the C-H vibration of surface-bound oleate ligands. Electron energy loss spectroscopy is used to map the strong near-field enhancement around these NCs that enables localized surface plasmon resonance (LSPR) coupling between adjacent nanocrystals and LSPR-molecular vibration coupling. Fourier transform infrared spectroscopy measurements and finite element simulations are applied to observe and explain the nature of the coupling phenomena, specifically addressing coupling in mesoscale assembled films. The Fano line shape signatures of LSPR-coupled molecular vibrations are rationalized with two-port temporal coupled mode theory. With this combined theoretical and experimental approach, we describe the influence of coupling strength and relative detuning between the molecular vibration and LSPR on the enhancement factor and further explain the basis of the observed Fano line shape by deconvoluting the combined response of the LSPR and molecular vibration in transmission, absorption and reflection. This study therefore illustrates various factors involved in determining the LSPR-LSPR and LSPR-molecular vibration coupling for metal oxide materials and provides a fundamental basis for the design of sensing or SEIRA substrates.

Gelation of plasmonic metal oxide nanocrystals by polymer-induced depletion attractions

“…S9-S10). The modest red-shift of the gel LSPR, its reduced peak intensity, and significant broadening towards lower energies compared to the spectrum of isolated NCs are all characteristic of LSPR coupling between NCs, as previously studied in extended assemblies, such as films, of colloidal metal NPs (76)(77)(78) and metal oxide NCs (49,79,80) . Therefore, the perturbations in the gel LSPR suggest structure-dependent coupling interactions between ITO NC nearest neighbors.…”

“…Although an idealized structural representation was used to ensure computational tractability, the simulated network was designed to approximate the experimentally measured NC volume fraction in the gel and the structural hierarchy ascertained from analysis of the SAXS data described earlier. As shown in Altogether, these findings highlight that depletion-attraction gelation of discrete NCs leverages the LSPR sensitivity to the local NC arrangement to extend the NC's intrinsic IR plasmonic range and diversify the optical response without suppressing the LSPR, and it allows generation of localized "hot spots", thereby providing coupling opportunities to other optical transitions relevant to surface enhanced infrared absorption spectroscopy (SEIRA) and sensing applications (10,49,81) otherwise inaccessible in networks of fused NCs.…”

Infrared‐Responsive Colloidal Silver Nanorods for Surface‐Enhanced Infrared Absorption

“…Some nanoantennas have also been employed for SEIRA, such as split‐ring metamaterials, pan‐shaped Au nanoantennas, and cruciform aperture arrays . In addition, colloidal metal nanostructures have been demonstrated as SEIRA platforms in a few studies, such as hexagonal close‐packed silica@Au nanoshell arrays and cubic F and Sn‐codoped In 2 O 3 nanocrystal arrays . For SEIRA, molecular vibrations in resonance with LSPRs can be largely enhanced by 10 3 –10 6 ‐folds owing to the strong local field enhancements of plasmonic nanostructures, and probe molecules are able to be detected by SEIRA down to the amol or even zmol level accordingly .…”

Complex refractive index spectra of whole blood and aqueous solutions of anticoagulants, analgesics and buffers in the mid-infrared

“…We also present the change in complex refractive index for the aqueous solutions relative to water to illustrate how this method can be implemented for sensing applications and allow design of optimised sensing devices. The reference data presented here will enable the optimised design of specific ultrasensitive biodiagnostic modalities, such as waveguide evanescent spectroscopy 3 – 10 or resonant antennas 25 – 27 , for detection of low concentrations of solutes at the point of care.…”