Situ Surface-enhanced Raman Scattering Research Articles

Voltage-Induced Inversion of Band Bending and Photovoltages at Semiconductor/Liquid Interfaces.

At semiconductor/liquid interfaces, the surface potential and photovoltages are produced by a combination of band bending and quasi-Fermi-level splitting at the semiconductor surface, which are usually treated in a qualitative fashion. As such, it is important to develop quantitative metrics for the band energies and photovoltaics at these interfaces. Here, we present a spectroscopic method for monitoring the photovoltages produced at semiconductor/liquid junctions. The surface reporter molecule mercaptobenzonitrile (MBN) is functionalized on the photoelectrode surface (p-type silicon) and is measured using in situ surface-enhanced Raman scattering (SERS) spectroscopy with a water immersion lens under electrochemical working conditions. In particular, the vibrational frequency of the C≡N stretch mode (ωCN) around 2225 cm-1 is sensitive to the local electric field in solution at the electrode/electrolyte interface via the vibrational Stark effect. Over the applied potential range from -0.8 to 0.6 V vs Ag/AgCl, we observe ωCN to increase from 2220 to 2229 cm-1 (at low laser power). As the incident laser power is increased from 83.5 μW to 13.3 mW, we observe additional shifts of ΔωCN = ±1 cm-1, corresponding to photovoltages produced at the semiconductor/liquid interface ΔV = ±0.2 V. Based on Mott-Schottky measurements, the flat band potential (FBP) occurs at -0.39 V vs Ag/AgCl. For applied potentials above the FBP, we observe ΔωCN > 0 (i.e., blue-shifts ∼1 cm-1) corresponding to positive photovoltages, whereas for applied potentials below the flat band potential, we observe ΔωCN < 0 (i.e., red-shifts ∼1 cm-1) corresponding to negative photovoltages. These spectroscopic observations reveal voltage-induced changes in the band bending at the semiconductor/liquid junction that, thus far, have been difficult to measure.

Surface-Enhanced Raman Spectroscopy for Boosting Electrochemical CO2 Reduction on Amorphous-Surfaced Tin Oxide Supported by MXene.

Amorphous materials disrupt the intrinsic linear scalar dependence seen in their crystalline counterparts, typically exhibiting enhanced catalytic characteristics. Nevertheless, substantial obstacles remain in terms of boosting their stability, enhancing their conductivity, and elucidating distinct catalytic mechanisms. Herein, a core-shell catalyst, comprising a crystalline SnO2 core and an amorphous SnOx shell supported on MXene (denoted as SnO2@SnOx/MXene), was prepared utilizing hydrothermal and solution reduction methods. The SnO2@SnOx/MXene catalyst excels in the electrocatalytic conversion of CO2 to formate, yielding a Faradaic efficiency (FE) as high as 93% for formate production at -1.17 V vs RHE and demonstrating exceptional durability. Both density functional theory (DFT) calculations and experimental results indicate that the SnOx shell bolsters formate formation by fine-tuning the adsorption energy of the *OCHO intermediate. In SnO2@SnOx/MXene, MXene plays a vital role in enhancing the conductivity and stability of the amorphous shell and especially amplifying Raman signals of catalyst components. The ex/in situ surface-enhanced Raman scattering (SERS) application further confirms the formation of amorphous SnOx and further enables the direct detection of the formation of the intermediate species. This work provides the basis for the application of amorphous materials in practical electrocatalytic reduction of CO2 reduction.

Strong plasmon resonance coupling in micro-extraction SERS membrane for in situ detection of molecular aqueous solutions

In situ surface-enhanced Raman scattering (SERS) detection of trace analytes with high sensitivity, especially in complex aqueous solution environments such as polluted water and biological fluids, remains an urgent task. Herein, a micro-extraction SERS membrane was developed by folding a plasmonic structure composing Au@Ag nanoparticles (NPs) and CuO nanospikes (NSs) via capillary action. In the numerical simulation using COMSOL software, we demonstrated that this structure with a parallel facing state can effectively trap and utilize incident photons to excite multiple plasmon resonance couplings. Moreover, it detected the molecular aqueous solution via capillary action in only 5 min. Benefitting from the dense volumetric hotspots and the simple trace extraction solution method, we utilized the proposed membrane for ultrasensitive in situ SERS detections of microcystin–LR (5 ×10–6 μg/L) toxins in drinking water, adenosine biological fluid (10–10 M), and carcinogenic malachite green (10–11 M) in seafood using a portable Raman instrument. The findings of this study provide promising insights for achieving in situ SERS detection of trace analytes in complex aqueous environments.

In Situ Raman Monitoring of Trace Antibiotics in Different Harsh Water Environments

In situ surface‐enhanced Raman scattering (SERS) is a widely used operando analytical technique, while facing numerous complex factors in applications under aqueous environment, such as low detection sensitivity, poor anti‐interference capability, etc., resulting in unreliable detectability. To address these issues, herein a new hydrophobic SERS strategy has been attempted. By comprehensively designing and researching a SERS‐active structure of superhydrophobic ZnO/Ag nanowires, we demonstrate that hydrophobicity can not only draw analytes from water onto substrate, but also adjust “hottest spot” from the bottom of the nanowires to the top. As a result, the structure can simultaneously concentrate the dispersed molecules in water and the enhanced electric field in structure into a same zone, while perfecting its own anti‐interference ability. The underwater in situ analytical enhancement factor of this platform is as high as 1.67 × 1011, and the operando limited of detection for metronidazole (MNZ) reaches to 10−9 M. Most importantly, we also successfully generalized this structure to various real in situ detection scenarios, including on‐site detection of MNZ in corrosive urine, real‐time warning of wrong dose of MNZ during intravenous therapy, in situ monitoring of MNZ in flowing wastewater with particulate interference, etc., demonstrating the great application potential of this hydrophobic platform. This work realizes a synergistic promotion for in situ SERS performance under aqueous environment, and also provides a novel view for improving other in situ analytical techniques.

Electrodeposition of copper from triethanolamine as a complexing agent in alkaline solution

The use of triethanolamine (TEA) as a cyanide-free electrolyte for copper electrodeposition was studied. The effect of TEA concentration on electrodeposition rate and cathodic adsorption during 3D copper growth was investigated. Linear sweep voltammetry (LSV), electrochemical quartz crystal microbalance (EQCM), scanning electron microscope (SEM), chronoamperometry and in situ surface-enhanced Raman scattering (SERS) were used to achieve a kinetic, thermodynamic, and mechanistic understanding. TEA forms stable complexes with copper, the most stable being Cu(TEA)(OH)3¯. Also, it acts as a surface modifier, promoting instantaneous nucleation and lower reduction rates to metallic copper. Thus, three-dimensional growth is controlled and, consequently, a smooth and homogeneous copper deposit is achieved.

Accelerated intermediate conversion through nickel doping into mesoporous Co-N/C nanopolyhedron for efficient ORR

Engineering non-precious metals into nitrogen-doped carbon is employed to improve electrocatalyst activity towards oxygen reduction reaction (ORR). A nickel-doped Co-N/C mesoporous nanopolyhedron is successfully evoluted from a Ni-doped ZIF-67 precursor. The Ni & Co synergistic N/C catalyst exhibits a half-wave potential of 0.895 V (vs. reversible hydrogen electrode (RHE)) with a diffusion-limiting current density of 6.1 mA cm−2 for alkaline ORR at 1600 r min−1, which is competitive to commercial Pt/C in terms of cost, methanol tolerance, and long-term stability. In situ surface-enhanced Raman scattering (SERS) study reveals the formation and fast conversion of superoxide ion (O2-) intermediate on the catalyst surface. Density functional theory (DFT) calculations demonstrate the decrease of energy barrier for potential-determining step (O* protonation) by Co-Ni synergy as well as the reduction of adsorption energy on catalyst surface upon nickel doping. The joint results of in situ SERS study and DFT calculations suggest a favourable ORR process on nickel-doped Co-N/C.

In Situ Monitoring of Palladium-Catalyzed Chemical Reactions by Nanogap-Enhanced Raman Scattering using Single Pd Cube Dimers

The central dilemma in label-free in situ surface-enhanced Raman scattering (SERS) for monitoring of heterogeneously catalyzed reactions is the need of plasmonically active nanostructures for signal enhancement. Here, we show that the assembly of catalytically active transition-metal nanoparticles into dimers boosts their intrinsically insufficient plasmonic activity at the monomer level by several orders of magnitude, thereby enabling the in situ SERS monitoring of various important heterogeneously catalyzed reactions at the single-dimer level. Specifically, we demonstrate that Pd nanocubes (NCs), which alone are not sufficiently plasmonically active as monomers, can act as a monometallic yet bifunctional platform with both catalytic and satisfactory plasmonic activity via controlled assembly into single dimers with an ∼1 nm gap. Computer simulations reveal that the highest enhancement factors (EFs) occur at the corners of the gap, which has important implications for the SERS-based detection of catalytic conversions: it is sufficient for molecules to come in contact with the "hot spot corners", and it is not required that they diffuse deeply into the gap. For the widely employed Pd-catalyzed Suzuki-Miyaura cross-coupling reaction, we demonstrate that such Pd NC dimers can be employed for in situ kinetic SERS monitoring, using a whole series of aryl halides as educts. Our generic approach based on the controlled assembly into dimers can easily be extended to other transition-metal nanostructures.

Investigating Lysosomal Autophagy via Surface-Enhanced Raman Scattering Spectroscopy.

Autophagy plays a critical role in many vitally important physiological and pathological processes, such as the removal of damaged and aged organelles and redundant proteins. Although autophagy is mainly a protective process for cells, it can also cause cell death. In this study, we employed in situ and ex situ surface-enhanced Raman scattering (SERS) spectroscopies to obtain chemical information of lysosomes of HepG2 cells. Results reveal that the SERS profiles of the isolated lysosomes are different from the in situ spectra, indicating that lysosomes lie in different microenvironments in these two cases. We further investigated the molecular changes of isolated lysosomes according to the autophagy induced by starvation via ex situ SERS. During autophagy, the conformation of proteins and the structures of lipids have been affected, and autophagy-related molecular evidence is given for the first time in the living lysosomes. We expect that this study will provide a reference for understanding the cell autophagy mechanism.

Monitoring Reaction Intermediates in Plasma-Driven SO2, NO, and NO2 Remediation Chemistry Using In Situ SERS Spectroscopy.

In situ surface-enhanced Raman scattering (SERS) spectroscopy is used to identify the key reaction intermediates during the plasma-based removal of NO and SO2 under dry and wet conditions on Ag nanoparticles. Density functional theory (DFT) calculations are used to confirm the experimental observations by calculating the vibrational modes of the surface-bound intermediate species. Here, we provide spectroscopic evidence that the wet plasma increases the SO2 and the NOx removal through the formation of highly reactive OH radicals, driving the reactions to H2SO4 and HNO3, respectively. We observed the formation of SO3 and SO4 species in the SO2 wet-plasma-driven remediation, while in the dry plasma, we only identified SO3 adsorbed on the Ag surface. During the removal of NO in the dry and wet plasma, both NO2 and NO3 species were observed on the Ag surface; however, the concentration of NO3 species was enhanced under wet-plasma conditions. By closing the loop between the experimental and DFT-calculated spectra, we identified not only the adsorbed species associated with each peak in the SERS spectra but also their orientation and adsorption site, providing a detailed atomistic picture of the chemical reaction pathway and surface interaction chemistry.

Roughened gold electrode for in situ SERS analysis of structural changes accompanying the doping process of polyaniline in acidic aqueous media

Electropolymerization of aniline on suitably roughened gold electrodes enabled us to record in situ surface-enhanced Raman scattering (SERS) spectra of polyaniline (PAni) during the doping-undoping process. Indeed, SERS-activation pretreatment of gold working electrode, using a specific electrochemical oxidation-reduction procedure, leads to the formation of countless surface asperities. The intergranular sites, known as “hot spots”, thus generated by the surface roughness are the seat of a strong electromagnetic coupling which leads to a huge SERS effect. Contrary to the case of platinum or mirror-polished gold electrodes, the use of roughened gold leads to high quality in situ SERS spectra of PAni, allowing the observation of important changes in the spectral features of its different oxidation states. In this study, we relied on spectral decomposition procedures to monitor and try to quantify these transformations accompanying the variation in the oxidation state of the polymer in different acidic aqueous solutions. In particular, the transition between the different forms of PAni (leucoemeraldine → emeraldine → pernigraniline), the drastic passage from benzenoid to quinoid structures of some aniline nuclei and the evolution of the charge-carrying structural defects are investigated despite the limitations imposed by the challenging conditions of the in situ analysis.

In situ monitoring of silver adsorption on assembled gold nanorods by surface-enhanced Raman scattering

Self-assembly of metal nanocrystals is able to create a gap of sub-nanometer distance for concentrating incoming light by the strong coupling of surface plasmon resonance, known as a ‘hot spot’. Although the plasmonic property of silver is better than other metals in the visible range, the superior Raman enhancement of silver compared to gold is still under debate. To provide direct evidence, in this work, we studied the silver adsorption on assembled gold nanorods (AuNRs) using in situ surface-enhanced Raman scattering (SERS) measurements. The self-assembled AuNR multimers were used as the SERS substrate, where the 4-mercaptophenol (MPh) molecules in our experiment played dual roles as both probe molecules for the Raman scattering and linking molecules for the AuNR assembly in a basic environment. Silver atoms were adsorbed on the surface of gold nanorod assemblies by reduction of Ag+ anions. The stability of the adsorbed silver was guaranteed by the basic environment. We monitored the SERS signal during the silver adsorption with a home-built in situ Raman spectroscope, which was synchronized by recording the UV–vis absorption spectra of the reaction solution to instantly quantify the plasmonic effect of the silver adsorption. Although a minor change was found in the plasmonic resonance wavelength or intensity, the measured SERS signal at specific modes faced a sudden increase by 2.1 folds during the silver adsorption. The finite element method (FEM) simulation confirmed that the silver adsorption corresponding to the plasmonic resonance variation gave little change to the electric field enhancement. We attributed the mode-specific enhancement mechanism of the adsorption of silver to the chemical enhancement from charge transfer (CT) for targeting molecules with a specific orientation. Our findings provided new insights to construct SERS substrates with higher enhancement factor (EF), which hopefully would encourage new applications in the field of surface-enhanced optical spectroscopies.

Water/Oil Interfacial Self-Assembled Gold Nanoarrays Modified on Transparent Tape for In Situ Surface-Enhanced Raman Scattering

Herein, a novel in situ surface-enhanced Raman scattering (SERS) method was proposed based on the prepared SERS substrate with good flexibility, excellent optical transparency, and high SERS activity. The SERS substrate was fabricated through the Au colloids injected with an ethanol and hexane mixture to form Au monolayer film (Au MLF) on the water/oil interface and followed by transferred to the sticky side of transparent tape after hexane volatilization. Transmission electron microscopy and scanning electron microscopy revealed that Au NPs with particle sizes of 25 nm were densely assembled and evenly distributed on the flexible and transparent tape. This Au MLF/tape was directly covered on the irregular shape samples and the detection signal was collected by the laser transmitting into the tape and interacting with the analytes. The optimal SERS signal intensity was obtained by tuning the concentration of Au colloid and addition volume of the mixture of ethanol and hexane to regulate the numbers of Au NPs on water/oil interface. The SERS intensity of six sample points selected randomly show a good repeatability with RSD = 4.92% (n = 6 × 8) and satisfying uniformity with RSD of 8.6% within an area of 4.0 × 4.0 μm. Also, the obtained Au MLF/tape SERS substrate showed good detection accuracy and recovery when used to detect residual malachite green (MG) residue on the surfaces of real fish samples with detection limit of 0.04 μmol/L (S/N = 3). Therefore, the developed Au MLF/tape SERS substrate has potential applications in the in situ SERS detection.

Monitoring Potential‐Induced DNA Dehybridization Kinetics for Single Nucleotide Polymorphism Detection by using In Situ Surface Enhanced Raman Scattering

AbstractChanges in temperature, ionic strength or electrical field are generally employed to dehybridize double‐stranded DNA (dsDNA). In contrast, we propose potential‐induced dsDNA dehybridization to distinguish fully matched target DNA (tDNA) from tDNA with a single nucleotide polymorphism (SNP) by following their dehybridization kinetics through in situ surface enhanced Raman scattering (SERS). The determination of the potential that evokes notable dehybridization of dsDNA without causing any desorption of the immobilized probe DNA (pDNA) from the electrode surface was performed by investigating the desorption kinetics of labelled single‐stranded DNA (ssDNA) and dehybridization kinetics of dsDNA with labelled tDNA. This comparatively simple approach allows for SNP detection within minutes.

In situ surface enhanced Raman spectroscopy detection in high pressure solution

In situ surface enhanced Raman scattering (SERS) in solution was tested in this study at ambient temperature and high pressure (up to 978MPa) in a diamond-anvil cell, with the intent of resolving trace detection in high pressure conditions. The 4-chlorothiophenol solution was used as the analyte in our experiments. A silver nanoparticle layer, formed by chemical reduction and assembled on a poly (allylamine hydrochloride)-modified silicon wafer, was used as the substrate. There was an obvious rise in SERS intensity when the sample chamber was pressurized for the first time in the diamond-anvil cell. But then the intensity drop occurred with increasing pressure and all peaks have pressure-induced blue shift below 700MPa. The SERS intensity and Raman shift displayed irregular changes in the pressure range from 700MPa to 978MPa. The discovery of the survival of in situ high-pressure SERS in solution in the present study may make it a prospecting tool for the high-precision detection of analyte in high pressure conditions. Moreover, it could provide more information on the SERS mechanisms that have been puzzling us for decades.

Effect of Water on the Product Distribution at the Cathode of Li-O2 Batteries

Li-O2 secondary batteries are attracting much researcher’s attentions as a candidate for the post lithium-ion secondary batteries due to the superior theoretical energy capacity. Oxygen reduction reaction forming Li2O2 deposition takes place at the cathode of Li-O2 secondary batteries during the discharge process. The theoretical capacity of the Li2O2 electrode (8 kWh L-1) is comparable to the energy density of diesel fuel (9.7 kWh L-1). However, the mechanisms of the cathode reactions are complicated and are not well understood. The trace amount of water in electrolyte solutions is known to affect the reaction mechanisms1,2 but how water affect the reactions are still under discussions. In this study, the effects of trace amount of water on the discharge product at gold electrode in the DMSO-based electrolyte solution are studied by using electrochemical quartz crystal microbalance (EQCM), rotating ring-disk electrode (RRDE) method, in situ surface enhanced Raman scattering (SERS) spectroscopy and other instrumental analysis. In situ SERS showed that ca.1000 ppm of water results in the decrease of crystal Li2O2 signal intensity and new peaks of LiHO2 and H2O2 at the initial stage of the discharge process. Application of negative potential, which causes surface mediated electrochemical reduction of LiO2 in the anhydrous electrolyte solution,3 results in the decomposition of DMSO forming Li2SO4 while amorphous phase of Li2O2 was formed in the anhydrous electrolyte solution. The series of decomposition reactions of DMSO induced by water clearly indicated by EQCM measurement as M/z = 55 g mol-1 corresponding to the formation of 1 mol of Li2SO4 by consumption of 2 mol of electron. These results show that effects of water should be considered when developing the better battery system utilizing water to change morphology of Li2O2 or converting Li2O2 to LiOH.1,2 References (1) D. G. Kwabi, T. P. Batcho, S. Feng, L. Giordano, C. V. Thompson and Y. Shao-Horn, Physical Chemistry Chemical Physics, 18, 24944 (2016). (2) F. Li, S. Wu, D. Li, T. Zhang, P. He, A. Yamada and H. Zhou, Nature Communications, 6, 7843 (2015). (3) D. G. Kwabi, M. Tułodziecki, N. Pour, D. M. Itkis, C. V. Thompson and Y. Shao-Horn, Journal of Physical Chemistry Letters, 7, 1204 (2016).

Silver Nanoprism-Loaded Eggshell Membrane: A Facile Platform for In Situ SERS Monitoring of Catalytic Reactions

We reported the fabrication of an in situ surface-enhanced Raman scattering (SERS) monitoring platform, comprised of a porous eggshell membrane (ESM) bioscaffold loaded with Ag nanoprism via an electrostatic self-assembly approach. The localized surface plasmon resonance (LSPR) property of silver nanoprism leads to the blue color of the treated ESMs. UV-vis diffuse reflectance spectroscopy, scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements were employed to observe the microstructure and surface property of Ag nanoprisms on the ESMs. The silver nanoprism-loaded eggshell membrane (AgNP@ESM) exhibited strong catalytic activity for the reduction of 4-nitrophenol by sodium borohydride (NaBH4) and it can be easily recovered and reused for more than six cycles. Significantly, the composites also display excellent SERS efficiency, allowing the in situ SERS monitoring of molecular transformation in heterogeneous catalysis. The results indicate that the AgNP@ESM biocomposite can achieve both SERS and catalytic functionalities simultaneously in a single entity with high performance, which promotes the potential applications of ESM modified with functional materials.

Temperature Effect on the Electrooxidation of Gamma Hydroxybutyric Acid (GHB) on Platinum Catalyst through Cyclic Voltammetry, Chronoamperometry, Impedance Spectroscopy and SERS Spectroelectrochemistry

A study of the electro-oxidation of gamma hydroxybutyric acid (GHB) on platinum electrode in acidic media has been investigated by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy in the temperature range between 5 and 30oC. The variation of the j-E curves allows the determination of activation energy in a wide interval of potentials where three characteristic oxidation peaks appear. The j-t curves were registered at the more positive potentials corresponding with the A and B peaks. Stationary current intensity measurements allowed the determination of the activation energy in pure kinetic region conditions. Electrochemical impedance spectroscopy made also possible the study of the electrochemical behavior in the same potential region. Temperature dependence of the charge-transfer resistance (Rct) and the rate constant associated with the surface coverage by an adsorbed intermediate (-1=Ro/L) during the GHB electro-oxidation process were evaluated and discussed. In all cases, the values of activation energy, below 30 kJ/mol, suggest that a complex mechanism takes place for the GHB electro-oxidation free of strong interactions with the platinum surface. In situ Surface Enhanced Raman Scattering (SERS) spectroelectrochemistry spectra corresponding to coadsorbed species, including intermediates of reaction, have been analyzed at several potentials.

Study of the electro-oxidation of a recreational drug GHB (gamma hydroxybutyric acid) on a platinum catalyst-type electrode through chronoamperometry and spectro-electrochemistry

The electro-oxidation of gamma-hydroxybutyric acid (GHB) on a polycrystalline platinum electrode in acidic medium has been studied using chronoamperometry and spectroelectrochemistry. The study has been performed in a wide interval of potentials and at different concentrations.It was found that at longer times the density currents reached stationary values over 0.3V whereas it is zero to potentials below the above mentioned. These characteristics in the j–t curves suggest a different mechanism for the electro-oxidation of GHB, potential dependent, with a catalytic process and an adsorption process controlled by mass transport in the respective potential regions indicated.The change in the stationary current obtained at +0.9V with variable GHB concentrations also suggests an oxidation mechanism catalysed by the platinum surface with platinum hydroxides acting as reaction intermediates to make the final oxidation product for GHB. The results obtained using chronoamperometry are in good agreement with those obtained using cyclic voltammetry where the alcohol group is oxidized at different potentials.In situ surface enhanced Raman scattering (SERS) spectra corresponding to GHB intermediates and water adsorbed species being formed/consumed at the potential-dependent adsorption processes have been analysed using spectro-electrochemistry. A peak at 1590cm−1, corresponding to the asymmetric stretching of carboxylic group in a bridge configuration, increases with the potential. This supports the hypothesis of a mechanism of formation of the succinic acid on the platinum surface as reaction product under the experimental conditions studied.

In situ SERS and X-ray photoelectron spectroscopy studies on the pH-dependant adsorption of anthraquinone-2-carboxylic acid on silver electrode

In this study, in situ surface-enhanced Raman scattering (SERS) spectroelectrochemistry and angle-resolved X-ray photoelectron spectroscopy (AR-XPS) are used to investigate the redox reaction and adsorption behavior of anthraquinone-2-carboxylic acid (AQ-2-COOH) on an Ag electrode at different pH values. The obtained results indicate that AQ-2-COOH is adsorbed tilted on the Ag electrode through O-atom of ring carbonyl in a potential range from −0.3 to −0.5V vs. SCE, but the orientation turns to more tilted orientation with both O-atom of the ring carbonyl and carboxylate group in positive potential region for pH 6.0 and 7.4. However, at pH 10.0, the orientation adopts tilted conformation constantly on the Ag electrode with both O-atom of the anthraquinone ring and carboxylate group in the potential range from −0.3 to −0.5V vs. SCE or at positive potentials. Moreover, the adsorption behavior of AQ-2-COOH has been further confirmed by AR-XPS on the Ag surface. Proposed reasons for the observed changes in orientation are presented.

Fabrication of Au@Pt multibranched nanoparticles and their application to in situ SERS monitoring.

Here, we present an Au@Pt core-shell multibranched nanoparticle as a new substrate capable of in situ surface-enhanced Raman scattering (SERS), thereby enabling monitoring of the catalytic reaction on the active surface. By careful control of the amount of Pt deposited bimetallic Au@Pt, nanoparticles with moderate performance both for SERS and catalytic activity were obtained. The Pt-catalyzed reduction of 4-nitrothiophenol by borohydride was chosen as the model reaction. The intermediate during the reaction was captured and clearly identified via SERS spectroscopy. We established in situ SERS spectroscopy as a promising and powerful technique to investigate in situ reactions taking place in heterogeneous catalysis.