Search

The progress of plasmon-based technologies relies on an understanding of the properties of the enhanced electromagnetic fields generated by the coupling nanostrucutres1–6. Plasmon-enhanced applications include advanced spectroscopies7–10, optomechanics11, optomagnetics12 and biosensing13–17. However, precise determination of plasmon field intensity distribution within a nanogap remains challenging. Here, we demonstrate a molecular ruler made from a set of viologen-based, self-assembly monolayers with which we precisely measures field distribution within a plasmon nanocavity with ~2-A spatial resolution. We observed an unusually large plasmon field intensity inhomogeneity that we attribute to the formation of a plasmonic comb in the nanocavity. As a consequence, we posit that the generally adopted continuous media approximation for molecular monolayers should be used carefully. The strength of the plasmonic field between a plasmonic particle and a Au surface can be measured at ~2-A resolution by following the Raman peaks of a suitably labelled self-assembly monolayer.

Shortly after a major renovation at the Royal Ontario Museum, it was noticed that the glass panels in many of the new display cases exhibited fogging or hazing on the surface, sometimes in ...

Surface-enhanced Raman scattering (SERS) is a powerful technique that provides fingerprint vibrational information with ultrahigh sensitivity. However, only a few metals (gold, silver and copper) yield a large SERS effect, and they must be rough at the nanoscale. Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was developed to overcome the long-standing materials and morphological limitations of SERS. It has already been applied in a variety of fields such as materials science, electrochemistry, surface science, catalysis, food safety and the life sciences. Here, the principles and applications of SHINERS are highlighted. To provide an understanding of the plasmonics involved, finite-difference time-domain (FDTD) calculations and single nanoparticle SHINERS experiments are reviewed. Next, various shell-isolated nanoparticle (SHIN) types are described. Then a number of applications are discussed. In the first application, SHINERS is used to characterize the adsorption processes of pyridine on Au(hkl) single-crystal electrode surfaces. Then, SHINERS' applicability to food inspection and cultural heritage science is demonstrated by the detection of parathion and fenthion pesticides, and Lauth's violet (thionine dye). Finally, graphene-isolated Au nanoparticles (GIANs) are shown to be effective for multimodal cell imaging, photothermal cancer therapy and photothermally-enhanced chemotherapy. SHINERS is a fast, simple and reliable method, suitable for application to many areas of science and technology. The concept of shell-isolation can also be applied to other surface-enhanced spectroscopies such as fluorescence, infrared absorption and sum frequency generation.

Electrochemical methods are combined with shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) for a comprehensive study of pyridine adsorption on Au(111), Au(100) and Au(110) single crystal electrode surfaces. The effects of crystallographic orientation, pyridine concentration, and applied potential are elucidated, and the formation of a second pyridine adlayer on Au(111) is observed spectroscopically for the first time. Electrochemical and SHINERS results correlate extremely well throughout this study, and we demonstrate the potential of EC-SHINERS for thorough characterization of processes occurring on single crystal surfaces. Our method is expected to open up many new possibilities in surface science, electrochemistry and catalysis. Analytical figures of merit are discussed.

Surface molecular information acquired in situ from a catalytic process can greatly promote the rational design of highly efficient catalysts by revealing structure-activity relationships and reaction mechanisms. Raman spectroscopy can provide this rich structural information, but normal Raman is not sensitive enough to detect trace active species adsorbed on the surface of catalysts. Here we develop a general method for in situ monitoring of heterogeneous catalytic processes through shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) satellite nanocomposites (Au-core silica-shell nanocatalyst-satellite structures), which are stable and have extremely high surface Raman sensitivity. By combining operando SHINERS with density functional theory calculations, we identify the working mechanisms for CO oxidation over PtFe and Pd nanocatalysts, which are typical low- and high-temperature catalysts, respectively. Active species, such as surface oxides, superoxide/peroxide species and Pd–C/Pt–C bonds are directly observed during the reactions. We demonstrate that in situ SHINERS can provide a deep understanding of the fundamental concepts of catalysis., Rational design of heterogeneous catalysts requires molecular understanding of catalytic processes. Here, the authors attach PtFe and Pd nanocatalysts to Raman signal-enhancing Au-silica nanoparticles, allowing them to spectroscopically observe the active species and bonds involved in CO oxidation in real time.