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Quantitative measurement of the plasmonic field distribution is of great significance for optimizing highly efficient optical nanodevices. However, the quantitative and precise measurement of the plasmonic field distribution is still an enormous challenge. In this work, we design a unique nanoruler with a ∼7 Å spatial resolution, which is based on a two-dimensional atomic crystal where the intercalated monolayer WS 2 is a surface-enhanced Raman scattering (SERS) probe and four layers of MoS 2 are a reference layer in a nanoparticle-on-mirror (NPoM) structure to quantitatively and directionally probe the longitudinal plasmonic field distribution at high permittivity by the quantitative SERS intensity of WS 2 located in different layers. A subnanometer two-dimensional atomic crystal was used as a spacer layer to overcome the randomness of the molecular adsorption and Raman vibration direction. Combined with comprehensive theoretical derivation, numerical calculations, and spectroscopic measurements, it is shown that the longitudinal plasmonic field in an individual nanocavity is heterogeneously distributed with an unexpectedly large intensity gradient. We analyze the SERS enhancement factor on the horizontal component, which shows a great attenuation trend in the nanocavity and further provides precise insight into the horizontal component distribution of the longitudinal plasmonic field. We also provide a direct experimental verification that the longitudinal plasmonic field decays more slowly in high dielectric constant materials. These precise experimental insights into the plasmonic field using a two-dimensional atomic crystal itself as a Raman probe may propel understanding of the nanostructure optical response and applications based on the plasmonic field distribution.

For the first time, we used the electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) technique to in situ characterize the adsorption behaviour of four DNA bases (adenine, guanine, thymine, and cytosine) on atomically flat Au(111) electrode surfaces. The spectroscopic results of the various molecules reveal similar features, such as the adsorption-induced reconstruction of the Au(111) surface and the drastic Raman intensity reduction of the ring breathing modes after the lifting reconstruction. As a preliminary study of the photo-induced charge transfer (PICT) mechanism, the in situ spectroscopic results obtained on single crystal surfaces are excellently illustrated with electrochemical data.

Point-of-care testing (POCT) with the advantages of speed, simplicity, portability, and low cost is critical for the measurement of analytes in a variety of environments where access to laboratory infrastructure is lacking. While qualitative POCTs are widely available, quantitative POCTs present significant challenges. Here we describe a novel method that integrates an Au core/Pt shell nanoparticle (Au@PtNP) encapsulated target-responsive hydrogel with a volumetric bar-chart chip (V-Chip) for quantitative POCT. Upon target introduction, the hydrogel immediately dissolves and releases Au@PtNPs, which can efficiently catalyze the decomposition of H2 O2 to generate a large volume of O2 to move of an ink bar in the V-Chip. The concentration of the target introduced can be visually quantified by reading the traveling distance of the ink bar. This method has the potential to be used for portable and quantitative detection of a wide range of targets without any external instrument., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Herein, we employ Ag@TiO2 core-shell nanoparticles for surface-enhanced Raman scattering (SERS) investigations of TiO2-N719 dye interfaces. In situ electrochemical SERS investigations of the Ag@TiO2-N719 interaction are systematically carried out under a series of electrode-potential controls. By comparing the potential dependence of resonant and pre-resonant SERS spectra recorded with different laser excitations, bidentate carboxylate linkage is considered to be involved in N719 adsorption on TiO2. Meanwhile, SCN ligand shows obvious interactions with TiO2, and their role in the adsorption and orientation of N719 on TiO2 should not be underestimated. The in situ SERS spectra of Ag@TiO2 show a clear bell-shaped intensity-potential relation for the major bands of N719. A molecule-to-TiO2 charge-transfer resonance is tentatively attributed to account for such a phenomenon. Under the influence of such a charge-transfer resonance, valuable information about the N719-TiO2 interaction as well as the intramolecular deformation of N719 is obtained., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Deduced from thermodynamics and the Thomson-Gibbs equation that the surface energy of crystal face is in proportion to the supersaturation of crystal growth units during the crystal growth, we propose that the exposed crystal faces can be simply tuned by controlling the supersaturation, and higher supersaturation will result in the formation of crystallites with higher surface-energy faces. We have successfully applied it for the growth of ionic (NaCl), molecular (TBPe), and metallic (Au, Pd) micro/nanocrystals with high-surface-energy faces. The above proposed strategy can be rationally designed to synthesize micro/nanocrystals with specific crystal faces and functionality toward specific applications.

Recently, it was found that Pt clusters deposited on Pd shell over Au core nanoparticles (Au@Pd@Pt NPs) exhibit unusually high electrocatalytic activity for the electro-oxidation of formic acid (P. P. Fang, S. Duan, et al., Chem. Sci., 2011, 2, 531-539). In an attempt to offer an explanation, we used here carbon monoxide (CO) as probed molecules, and applied density functional theory (DFT) to simulate the surface Raman spectra of CO at this core-shell-cluster NPs with a two monolayer thickness of Pd shell and various Pt cluster coverage. Our DFT results show that the calculated Pt coverage dependent spectra fit the experimental ones well only if the Pt clusters adopt a mushroom-like structure, while currently the island-like structure is the widely accepted model, which follows the Volmer-Weber growth mode. This result infers that there should be a new growth mode, i.e., the mushroom growth mode as proposed in the present work, for Au@Pd@Pt NPs. We suggest that such a mushroom-like structure may offer novel active sites, which accounts for the observed high electrocatalytic activity of Au@Pd@Pt NPs.

The aim of this work is to further improve the molecular generality and substrate generality of SERS (i.e., to fully optimize the SERS activity of transition-metal electrodes). We utilized a strategy of borrowing high SERS activity from the Au core based on Au-core Pt-shell (Au@Pt) nanoparticle film electrodes, which can be simply and routinely prepared. The shell thickness from about one to five monolayers of Pt atoms can be well controlled by adjusting the ratio of the number of Au seeds to Pt(IV) ions in the solution. The SERS experimental results of carbon monoxide adsorption indicate that the enhancement factor for the Au@Pt nanoparticle film electrodes is more than 2 orders of magnitude larger than that of electrochemically roughened Pt electrodes. The practical virtues of the present film electrodes for obtaining rich and high-quality vibrational information for diverse adsorbates on transition metals are pointed out and briefly illustrated with systems of CO, hydrogen, and benzene adsorbed on Pt. We believe that the electrochemical applications of SERS will be broadened with this strategy, in particular, for extracting detailed vibrational information for adsorbates at transition-metal electrode interfaces.

Carbon-supported nanoparticles are indispensable to enabling new energy technologies such as metal-air batteries and catalytic water splitting. However, achieving ultrasmall and high-density nanoparticles (optimal catalysts) faces fundamental challenges of their strong tendency toward coarsening and agglomeration. Herein, we report a general and efficient synthesis of high-density and ultrasmall nanoparticles uniformly dispersed on two-dimensional porous carbon. This is achieved through direct carbothermal shock pyrolysis of metal-ligand precursors in just ~100 ms, the fastest among reported syntheses. Our results show that the in situ metal-ligand coordination (e.g., N → Co2+) and local ordering during millisecond-scale pyrolysis play a crucial role in kinetically dominated fabrication and stabilization of high-density nanoparticles on two-dimensional porous carbon films. The as-obtained samples exhibit excellent activity and stability as bifunctional catalysts in oxygen redox reactions. Considering the huge flexibility in coordinated precursors design, diversified single and multielement nanoparticles (M = Fe, Co, Ni, Cu, Cr, Mn, Ag, etc) were generally fabricated, even in systems well beyond traditional crystalline coordination chemistry. Our method allows for the transient and general synthesis of well-dispersed nanoparticles with great simplicity and versatility for various application schemes. Well-dispersed nanoparticles are critical for catalysis but face challenges of easy agglomeration. Here the authors report synthesis of ultrasmall nanoparticles anchored on two-dimensional porous carbon via coordinated carbothermal shock and the application of resulted nanoparticles as catalysts for oxygen electrocatalysis. [ABSTRACT FROM AUTHOR]

Developing advanced characterization techniques for single‐atom catalysts (SACs) is of great significance to identify their structural and catalytic properties. Raman spectroscopy can provide molecular structure information, and thus, the technique is a promising tool for catalysis. However, its application in SACs remains a great challenge because of its low sensitivity. We develop a highly sensitive strategy that achieves the characterization of the structure of SACs and in situ monitoring of the catalytic reaction processes on them by shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) for the first time. Using the strategy, Pd SACs on different supports were identified by Raman spectroscopy and the nucleation process of Pd species from single atoms to nanoparticles was revealed. Moreover, the catalytic reaction processes of the hydrogenation of nitro compounds on Pd SACs were monitored in situ, and molecular insights were obtained to uncover the unique catalytic properties of SACs. This work provides a new spectroscopic tool for the in situ study of SACs, especially at solid–liquid interfaces. [ABSTRACT FROM AUTHOR]

Abstract: Heterogeneous metal interfaces play a key role in determining the mechanism and performance of catalysts. However, in situ characterization of such interfaces at the molecular level is challenging. Herein, two model interfaces, Pd and Pt overlayers on Au single crystals, were constructed. The electronic structures of these interfaces as well as effects of crystallographic orientation on them were analyzed by shell‐isolated nanoparticle‐enhanced Raman spectroscopy (SHINERS) using phenyl isocyanide (PIC) as a probe molecule. A clear red shift in the frequency of the C≡N stretch (νNC) was observed, which is consistent with X‐ray photoelectron spectroscopy (XPS) data and indicates that the ultrathin Pt and Pd layers donate their free electrons to the Au substrates. Furthermore, in situ electrochemical SHINERS studies showed that the electronic effects weaken Pt−C/Pd−C bonds, leading to improved surface activity towards CO electrooxidation. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Surface plasmon resonances (SPRs) have been found to promote chemical reactions. In most oxidative chemical reactions oxygen molecules participate and understanding of the activation mechanism of oxygen molecules is highly important. For this purpose, we applied surface-enhanced Raman spectroscopy (SERS) to find out the mechanism of SPR-assisted activation of oxygen, by using p-aminothiophenol (PATP), which undergoes a SPR-assisted selective oxidation, as a probe molecule. In this way, SPR has the dual function of activating the chemical reaction and enhancing the Raman signal of surface species. Both experiments and DFT calculations reveal that oxygen molecules were activated by accepting an electron from a metal nanoparticle under the excitation of SPR to form a strongly adsorbed oxygen molecule anion. The anion was then transformed to Au or Ag oxides or hydroxides on the surface to oxidize the surface species, which was also supported by the heating effect of the SPR. This work points to a promising new era of SPR-assisted catalytic reactions. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) is a powerful spectroscopy technique that can provide non-destructive and ultra-sensitive characterization down to single molecular level, comparable to single-molecule fluorescence spectroscopy. However, generally substrates based on metals such as Ag, Au and Cu, either with roughened surfaces or in the form of nanoparticles, are required to realise a substantial SERS effect, and this has severely limited the breadth of practical applications of SERS. A number of approaches have extended the technique to non-traditional substrates, most notably tip-enhanced Raman spectroscopy (TERS) where the probed substance (molecule or material surface) can be on a generic substrate and where a nanoscale gold tip above the substrate acts as the Raman signal amplifier. The drawback is that the total Raman scattering signal from the tip area is rather weak, thus limiting TERS studies to molecules with large Raman cross-sections. Here, we report an approach, which we name shell-isolated nanoparticle-enhanced Raman spectroscopy, in which the Raman signal amplification is provided by gold nanoparticles with an ultrathin silica or alumina shell. A monolayer of such nanoparticles is spread as ‘smart dust’ over the surface that is to be probed. The ultrathin coating keeps the nanoparticles from agglomerating, separates them from direct contact with the probed material and allows the nanoparticles to conform to different contours of substrates. High-quality Raman spectra were obtained on various molecules adsorbed at Pt and Au single-crystal surfaces and from Si surfaces with hydrogen monolayers. These measurements and our studies on yeast cells and citrus fruits with pesticide residues illustrate that our method significantly expands the flexibility of SERS for useful applications in the materials and life sciences, as well as for the inspection of food safety, drugs, explosives and environment pollutants. [ABSTRACT FROM AUTHOR]

In-situ Raman/SERS studies of molecular adsorption/reaction behaviors at well-defined electrochemical interfaces are important for understanding the fundamentals of electrochemical processes. However, it is still a great challenge to perform such studies on model single-crystal surfaces as the smooth surface cannot support surface plasmon resonance (SPR). In this work, shell-isolated nanoparticle-enhanced Raman spectroscopy was combined with an electrochemical method (EC-SHINERS) to study the adsorption and redox transformation of a resonant molecule viologen HS-8V8H at Au(hkl) single-crystal electrodes. Changes in the molecular structure with potential were identified on different single-crystal surfaces, which explained the transformation process of viologen from V 2 + state to V + and then V 0 . Facet-dependent SERS enhancement was also observed, which results from the different imaginary part of the dielectric function on Au(111), Au(100) and Au(110), and is supported by the FEM simulations. Furthermore, a nonlinear resonant Raman process has been directly observed in our experiments, which is consistent with the simulation results. These findings increase our understanding of the electrochemical behavior of molecules in model systems. [ABSTRACT FROM AUTHOR]

Recently we developed shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) as a new variant of surface-enhanced Raman spectroscopy (SERS). The most important feature of SHINERS is its capability to study electrochemical single-crystal electrode surfaces, e.g., gold, platinum, palladium, rhodium and silicon. The gold-core silica-shell nanoparticles can significantly boost the Raman intensity from adsorbates on atomically flat surfaces. Very surprisingly the average enhancement factor can reach 10 6 for Au(110) and 10 5 for Pt(110). To understand this extraordinary high enhancement, we explore the mechanism on why SHINERS works so well for single-crystal electrode of diverse materials by classical electromagnetic simulations. We then performed the periodic DFT calculations of the polarizability of clean and pyridine-modified surfaces and the Raman intensity of adsorbates to reveal the interesting phenomenon regarding surface-crystal-orientation dependence of SHINERS intensity. Finally, prospective developments of EC-SHINERS are discussed. [ABSTRACT FROM AUTHOR]

Locally probing chemical reactionsor catalytic processes on surfacesunder realistic reaction conditions has remained one of the main challengesin materials science and heterogeneous catalysis. Where conventionalsurface interrogation techniques usually require high-vacuum conditionsor ensemble average measurements, plasmonic nanoparticles excel inextreme light focusing and can produce highly confined electromagneticfields in subwavelength volumes without the need for complex near-fieldmicroscopes. Here, we demonstrate an all-optical probing techniquebased on plasmonic smart dust for monitoring local chemical reactionsin real time. The silica shell-isolated gold nanoparticles that formthe smart dust can work as strong light concentrators and opticallyreport subtle environmental changes at their pinning sites on theprobed surface during reaction processes. As a model system, we investigatethe hydrogen dissociation and subsequent uptake trajectory in palladiumwith both “dust-on-film” and “film-on-dust”platforms. Using time-resolved single particle measurements, we demonstratethat our technique can in situ encode chemical reaction informationas optical signals for a variety of surface morphologies. The presentedtechnique offers a unique scheme for real-time, label-free, and high-resolutionprobing of local reaction kinetics in a plethora of important chemicalreactions on surfaces, paving the way toward the development of inexpensiveand high-output reaction sensors for real-world applications. [ABSTRACT FROM AUTHOR]

Abstract: The invention of shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) extends the study of Raman spectroscopy into surface electrochemistry on the SERS-inactive smooth electrodes. This work aims to investigate the electrochemical system perturbation brought about by spreading Au–core silica–shell nanoparticles (Au@SiO2 NPs) over the electrode surface for SHINERS. The differential capacitance measurements have shown SHINERS to cause the minimum of disturbance in the electrochemical system. The spectral features of SHINERS of pyridine adsorbed at smooth silver electrodes differs from that of SERS on the electrochemically roughened surface because pyridine interacts with silver much more strongly on the roughened electrode with many heterogeneous adsorption sites. Since most electrochemical data about surface adsorption are based on mechanically polished surface, the spectral information provided by the in situ SHINERS could be more reliable and better correlation. [Copyright &y& Elsevier]

We very recently reported a new spectroscopic application for expanding the versatility of surface Raman called “shell-isolated nanoparticle-enhanced Raman spectroscopy” or “SHINERS”. The most important and most difficult part of the SHINERS experiment is the effective transfer of the strong electromagnetic field from a gold core through the isolating silica or alumina shell to the probed surface. For this it is essential that the chemically inert dielectric shell be ultrathin (2–5 nm) yet pinhole-free. Herein we describe experimental and theoretical aspects of our SHINERS method in more detail. We provide a protocol for the synthesis and characterization of optimized shell-isolated nanoparticles (SHINs), and we examine the advantages of SHINERS nanoparticles over bare gold nanoparticles. We also present high-quality Raman spectra obtained from gold and platinum single-crystal surfaces in an electrochemical environment by our SHINERS technique. SHINERS is a simple and cost-effective approach that expands the flexibility of surface-enhanced Raman scattering (SERS) for an unprecedented diversity of applications in materials and surface sciences. [ABSTRACT FROM AUTHOR]

Abstract: Au core Pd shell (Au@Pd) nanoparticles with controllable size from 35 to 100nm were prepared by chemical deposition of Pd over pre-formed 12nm Au seeds. Both transmission electron microscopy and UV–visible spectroscopy studies confirmed the core–shell structure of the synthesized nanoparticles. The Au@Pd nanoparticles dispersed on a polished Pt electrode surface exhibit high surface-enhanced Raman scattering (SERS) effect for the adsorbed pyridine and SCN−. With the aid of the long-range effect of the electromagnetic (EM) enhancement created by the SERS-active Au core underneath the Pd shell, the good quality SERS spectra of adsorbates on the palladium metal overlayer can be obtained. Such kind of SERS-active substrate can be used as an alternative substrate to massive metals for investigating adsorption and reactions occurring on the Pd metal catalyst. [Copyright &y& Elsevier]

Reductive removal of the organochlorine herbicide alachlor on Ni-coated graphite felt modified with Ag nanoparticles (Ag/Ni@GF) was studied. Ag/Ni@GF was prepared by spontaneous deposition of silver onto Ni-coated graphite felt (Ni@GF), which was previously obtained by electrodeposition of Ni onto graphite felt (GF). Interestingly, Ag/Ni@GF exhibited a high specific surface area of 26 m2 g−1 determined by the Brunauer-Emmett-Teller (BET) method and a high Ag loading of 13.7 mg cm−3 as shown by electrochemical analyses. Alachlor (50 mg L−1 in 0.05 M NaOH) was successfully reduced at −0.9 V vs. mercury- mercurous sulfate electrode with 96% conversion efficiency and a current efficiency up to 33%. The main by-product was its dechlorinated derivative, deschloroalachlor, obtained with 76% yield. Surface-enhanced Raman scattering (SERS) showed that PVP, necessary to control Ag nanoparticles deposition, does not affect the catalytic activity of Ag. Ag/Ni@GF electrodes could be used several times, highlighting their good stability. Unlabelled Image • Spontaneous deposition of Ag nanoparticles on Ni-coated graphite felt was performed. • The modified electrode exhibits a high specific surface area and a high Ag loading. • The reductive dechlorination of alachlor was performed with good selectivity. • The modified electrode shows a remarkable stability after several electrolyses. [ABSTRACT FROM AUTHOR]