Cascaded nanooptics to probe microsecond atomic-scale phenomena

Abstract

<jats:p>Plasmonic nanostructures can focus light far below the diffraction limit, and the nearly thousandfold field enhancements obtained routinely enable few- and single-molecule detection. However, for processes happening on the molecular scale to be tracked with any relevant time resolution, the emission strengths need to be well beyond what current plasmonic devices provide. Here, we develop hybrid nanostructures incorporating both refractive and plasmonic optics, by creating SiO<jats:sub>2</jats:sub>nanospheres fused to plasmonic nanojunctions. Drastic improvements in Raman efficiencies are consistently achieved, with (single-wavelength) emissions reaching 10<jats:sup>7</jats:sup>counts⋅mW<jats:sup>−1</jats:sup>⋅s<jats:sup>−1</jats:sup>and 5 × 10<jats:sup>5</jats:sup>counts∙mW<jats:sup>−1</jats:sup>∙s<jats:sup>−1</jats:sup>∙molecule<jats:sup>−1</jats:sup>, for enhancement factors &gt;10<jats:sup>11</jats:sup>. We demonstrate that such high efficiencies indeed enable tracking of single gold atoms and molecules with 17-µs time resolution, more than a thousandfold improvement over conventional high-performance plasmonic devices. Moreover, the obtained (integrated) megahertz count rates rival (even exceed) those of luminescent sources such as single-dye molecules and quantum dots, without bleaching or blinking.</jats:p>

Dynamics of deterministically positioned single‐bond surface‐enhanced Raman scattering from DNA origami assembled in plasmonic nanogaps

“…Optimized collection geometries could further improve the photon yield to >10 5 mW/μm 2 /s, allowing us to observe the dynamics at millisecond resolution. [ 42 ]…”

“…Optimized collection geometries could further improve the photon yield to >10 5 mW/μm 2 /s, allowing us to observe the dynamics at millisecond resolution. [42] The C≡C bond vibrations show spectral wandering of Δν apprximately 5 to 10 cm −1 on timescales of 1 s (Figure 2b). These shifts are 2 × smaller than the smallest linewidth observed in the time series spectra.…”

Advances of surface-enhanced Raman and IR spectroscopies: from nano/microstructures to macro-optical design

“…For macro-optics, scanning microsphere microscopy, which has gained widespread attention in recent years, converges excitation light into a nanojet through a micro-scale dielectric sphere 109 . The combination of scanning microspheres with plasmon-enhanced substrates is expected to widen the application area of SERS 104 .…”

“…In 2020, Baumberg’s group developed cascaded nano optics structures incorporating both refractive and plasmonic optics, by creating SiO 2 microlens fused to Au nanoparticle 104 . They routinely achieved significant improvements in SERS efficiencies, with (single-wavelength) emissions reaching 10 7 counts mW −1 s −1 and 5 × 10 5 counts mW −1 s −1 molecule −1 , for enhancement factors >10 11 .…”

Editorial: Novel SERS-Active Materials and Substrates: Sensing and (Bio)applications

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Editorial on the Research TopicNovel SERS-active Materials and Substrates: Sensing and (Bio)ApplicationsNearly 50 years have passed since the encounter of the surface-enhanced Raman scattering (SERS) phenomenon, which had a bumpy ride from a misinterpreted discovery to well-planned applications. SERS enhancement factors-defined as the intensity ratio between SERS and conventional Raman scattering signal for a given analyte normalized by the number of molecules probed-can typically achieve 8-10 orders of magnitude for the plasmonic substrates with inter-/intra-particle nanogap, while these values can exceed 10 11 , in case of, to name one example, cascaded nanooptical structures combining refractive and plasmonic optics (Kamp et al, 2020). However, reliable estimation of SERS enhancement factor, as well as fabrication of SERS-active materials and substrates guaranteeing reproducibility of SERS signal, controlled optical properties and interactions with the examined molecules, and viable quantitative analysis employing SERS spectroscopy are still the most challenging issues to overcome the limitations of SERS in order to become a routine analytical technique.Recent years have been extremely advantageous to SERS spectroscopy, which, thanks to the development of nanotechnology and progress towards a higher level of the theory-in tandem with an improved detection sensitivity of Raman instruments and advances in computing power capacities-has grown to a role that goes beyond purely academic applications.All of these, together with an enormous enhancement of the intrinsically weak Raman scattering signal, supported by high selectivity and specificity of the SERS method, offer simple detection and identification of the analyte of interest and use for designed applications.Nowadays, a smart combination of computational approaches and vibrational spectroscopy aids the interpretation of SERS experimental results (Królikowska et al, 2020).

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