Showing papers by "Bin Ren published in 2010"

Shell-isolated nanoparticle-enhanced Raman spectroscopy

Abstract: 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.

When the signal is not from the original molecule to be detected: chemical transformation of para-aminothiophenol on Ag during the SERS measurement.

Abstract: Surface-enhanced Raman spectroscopy (SERS) has long been considered as a noninvasive technique that can obtain the fingerprint vibrational information of surface species. We demonstrated in this paper that a laser with a power level considered to be low in the traditional SERS measurement can already lead to a significant surface reaction. para-Aminothiophenol, an important probe molecule in SERS, was found to be oxidized to form 4,4'-dimercaptoazobenzene (DMAB) on a roughened silver surface during the SERS measurement. The assumption was confirmed experimentally by surface mass spectroscopy and SERS as well as electrochemistry of the synthesized DMAB, which agrees well with theoretical calculations. A defocusing method was used to avoid the laser induced surface reaction and perform reliable SERS characterization and identification, which can effectively avoid erroneous interpretation of the distorted experimental result.

In situ identification of intermediates of benzyl chloride reduction at a silver electrode by SERS coupled with DFT calculations.

Abstract: Aiming to deeply understand the electrocatalytic mechanism of silver on reduction of benzyl chloride, we carried out an in situ electrochemical surface-enhanced Raman spectroscopic study to characterize various surface species in different electrode potential regions. A further analysis with DFT calculation reveals that the benzyl radical and its anionic derivate bonded on a silver electrode are the key intermediates, implying that the pathway could drastically differ from the outer sphere concerted electron reduction at inert electrodes.

Bridging the gap between electrochemical and organometallic activation: benzyl chloride reduction at silver cathodes.

Abstract: Integration of voltammetry, surface-enhanced Raman spectroscopy (SERS), and density functional theory (DFT) has allowed unraveling the mechanistic origin of the exceptional electrocatalytic properties of silver cathodes during the reduction of benzyl chloride. At inert electrodes the initial reduction proceeds through a concerted direct electron transfer yielding a benzyl radical as the first intermediate. Conversely, at silver electrodes it involves an uphill preadsorption of benzyl chloride onto the silver cathode. Reduction of this adduct affords a species tentatively described as a distorted benzyl radical anion stabilized by the silver surface. This transient species rapidly evolves to yield ultimately a benzyl radical bound onto the silver surface, the latter being reduced into a benzyl-silver anionic adduct which eventually dissociates into a free benzyl anion at more negative potentials. Within this framework, the exceptional electrocatalytic properties of silver cathodes stem from the fact that they drastically modify the mechanism of the 2e-reduction pathway through a direct consequence of the electrophilicity of silver cathode surfaces toward organic halides. This mechanism contrasts drastically with any of those tentatively invoked previously, and bridges classical electroreduction mechanisms and oxidative additions similar to those occurring during organometallic homogeneous activation of organic halides by low-valent transition-metal complexes.

SERS and DFT study of water on metal cathodes of silver, gold and platinum nanoparticles.

Abstract: The observed surface-enhanced Raman scattering (SERS) spectra of water adsorbed on metal film electrodes of silver, gold, and platinum nanoparticles were used to infer interfacial water structures on the basis of the change of the electrochemical vibrational Stark tuning rates and the relative Raman intensity of the stretching and bending modes. To explain the increase of the relative Raman intensity ratio of the bending and stretching vibrations at the very negative potential region, density functional theory calculations provide the conceptual model. The specific enhancement effect for the bending mode was closely associated with the water adsorption structure in a hydrogen bonded configuration through its H-end binding to surface sites with large polarizability due to strong cathodic polarization. The present results allow us to propose that interfacial water molecules exist on these metal cathodes with different hydrogen bonding interactions, i.e., the HO–H⋯H–Pt dihydrogen bond for platinum and the HO–H⋯Ag(Au) for silver and gold. This dihydrogen bonding configuration on platinum is further supported from observation of the Pt–H stretching band. Furthermore, the influences of the pH effect on SERS intensity and vibrational Stark effect on the gold electrode indicate that the O–H stretching SERS signals are enhanced in the alkaline solutions because of the hydrated hydroxide surface species adsorbed on the gold cathode.

FDTD for plasmonics: Applications in enhanced Raman spectroscopy

Abstract: The exact electromagnetic enhancement mechanism behind SERS, TERS, HERS and SHINERS is one of the issues focused on in the study of enhanced Raman spectroscopy. The three dimensional finite difference time domain method (3D-FDTD), which is widely used in nanoplasmonic simulations, not only provides us with a powerful numerical tool for theoretical studies of the ERS electromagnetic enhancement mechanism, but also serves as a useful tool for the design of ERS-active systems with higher sensitivities and spectral spatial resolution. In this paper, we first introduce the fundamental principles of FDTD algorithms, and then the size-dependent dielectric function of dispersive metallic material is discussed. A comparative study of FDTD and rigorous Mie evaluations of electromagnetic fields in the vicinity of a system of self-similar nanospheres shows an excellent correlation between the two computational methods, directly confirming the validity and accuracy of 3D-FDTD simulations in ERS calculations. Finally, we demonstrate, using a TERS calculation as an example, that the non-uniform mesh method can be more computationally efficient without loss of accuracy if it is applied correctly.

Charge-Transfer Enhancement Involved in the SERS of Adenine on Rh and Pd Demonstrated by Ultraviolet to Visible Laser Excitation

Abstract: Natural Science Foundation of China [20825313, 20827003, 20973143, 20903076]; MOST of China [2009CB930703]

Potential-Dependent Chemisorption of Carbon Monoxide at a Gold Core-Platinum Shell Nanoparticle Electrode: A Combined Study by Electrochemical in Situ Surface-Enhanced Raman Spectroscopy and Density Functional Theory

Abstract: National Natural Science Foundation of China (NSFC) [20773116]; Chinese Academy of Sciences; Ministry of Science and Technology of China [2010CB923302]; State Key Laboratory of Physical Chemistry of Solid Surfaces of Xiamen University [200706]; Education

Vibrational Signature of Double‐End‐Linked Molecules at Au Nanojunctions Probed by Surface‐Enhanced Raman Spectroscopy

Abstract: National Basic Research Program of China [2009CB930703, 2007CB935603, 2007DFC40440]; Natural Science Foundation of China [20673086, 20620130427, 20825313, 20827003]; NFFTBS [J0630429]; NCETFJ ; HPC of Xiamen University

Shelled-isolated nanoparticle-enhanced Raman spectroscopy

Abstract: S1. Supplementary Methods S1.1. Preparation of Au@SiO2 core-shell NPs We first synthesized Au NPs with a diameter of about 55 nm as cores by a standard sodium citrate reduction method. A freshly prepared aqueous solution of 1 mM (3-Aminopropyl) trimethoxysilane (APS) was added to the gold sol under vigorous magnetic stirring in 15 min, ensuring complete complexation of the amine groups with the gold surface. Then a 0.54 wt% sodium silicate solution was added to the sol, again under vigorous magnetic stirring. To accelerate the synthesis procedure and make the ultra-thin silica shell, we elevated the reaction temperature from room temperature to 90 C, so that the original coating time of 2-3 days for coating silica shells of 4-5 nm can be shortened to ca. one hour. More importantly, this method ensures to form the ultra-thin shell thickness of only 2-4 nm that is free of pinholes (see S8) by carefully controlling parameters such as reaction time, temperature, pH, and the concentration.

Facile electrochemical preparation of Ag nanothorns and their growth mechanism.

Abstract: National Science Foundation of China [20775015, 211735002, 20975022]; National Basic Research Program of China [2010CB732403]; MOE [20070386005]; NCETTFJ [XSRC2007-02]; State Key Laboratory of Physical Chemistry of Solid Surfaces of Xiamen University

On the Criteria of Instability for Electrochemical Systems

Abstract: Both cyclic-voltammetry-based and impedance-based experimental criteria that have been developed recently for the oscillatory electrochemical systems are critically appraised with two typical categories of oscillators. Consistent conclusions can be drawn by the two criteria for the category of oscillators that involve the coupling of charge transfer mainly with surface steps (e.g. ad- and desorption) such as in the electrooxidation of C1 organic molecules. Whereas, impedance-based criterion is not applicable to the category of oscillators that involve the coupling of charge transfer mainly with mass transfer (e.g. diffusion and convection) such as in the Fe(CN)63- reduction accompanying periodic hydrogen evolution. The reason is that the negative impedance cannot include the feedback information of convection mass transfer induced by the hydrogen evolution. However, both positive and negative nonlinear feedbacks, i. e., the diffusion-limited depletion and convection-enhanced replenishment of the Fe(CN)63- surface concentration, that coexist between the bistability, i.e., Fe(CN)63- reduction with and without hydrogen evolution at lower and higher potential sides respectively, are all reflected in the crossed cyclic voltammogram (CCV). It can be concluded that the voltammetry-based criterion (in time domain) is more intuitive, less time-consuming and has a wider range of applications than the impedance-based one (in frequency domain).

Surface bonding on silicon surfaces as probed by tip-enhanced Raman spectroscopy

Abstract: National Natural Science Foundation of China [20673086, 20827003, 20825313]; 973 Program [2009CB930703, 2007CB935603]; Fok Ying Tung Foundation [101015]

The Relationship Between Extraordinary Optical Transmission and Surface-Enhanced Raman Scattering in Subwavelength Metallic Nanohole Arrays

Abstract: Nanohole arrays in an Ag film were used as a substrate for surface-enhanced Raman scattering in the optical range. Extraordinary optical transmission and local field enhancement in Ag nanohole arrays were theoretically simulated using three-dimensional finite difference time domain method. The periodicity of the holes was adjusted to control the transmission intensity and electric field intensity. The calculation results show that the peak position of transmission red-shifts as the periodicity increases, while the peak intensity decreases linearly. The electric field is localized in a very small region at the edges of the holes, which means the surface-enhanced Raman scattering originates only from a small number of molecules located in the edge regions. The electric field intensity changes with the excitation wavelength in a similar trend to the transmission intensity. Both the electric field intensity and transmission intensity reach their maximum value at the frequency of surface plasmon resonance. The structure that gives resonant transmission provides the maximum surface-enhanced Raman scattering signal. Controllable and predictable surface-enhanced Raman scattering can be produced by using this novel nanostructure. The structure can be optimized to get the maximum surface-enhanced Raman scattering signal at a certain excitation wavelength through numerical simulations.

Near-field coupling and SERS effects of palladium nanoparticle dimers

Abstract: National Natural Science Foundation of China [20703032]; National Basic Research Program of China [2009CB930703]; Natural Science Foundation of Fujian Province of China [E0710028]

Electrocatalytic Oxidation of Formic Acid on Pt-Se Hollow Nanosphere Modified Glassy Carbon Electrodes

Abstract: National Natural Science Foundation of China [20663002]; Foundation of State Key Laboratory of Physical Chemistry of Solid Surfaces, Xiamen University, China [200511]

9 Electrochemical SERS and its Application in Analytical, Biophysical and Life Science

Abstract: Raman spectroscopy, as a vibrational spectroscopy, can record fingerprint spectra from electrodes and provide much insight into a variety of surface and interfacial processes at the molecular level: for example, qualitatively determining surface bonding, conformation and orientation. Raman spectroscopy invariably uses lasers from the ultraviolet (UV) to the near infrared (NIR). More importantly, the technique can be applied in situ to investigate solid–liquid, solid–gas and solid–solid interfaces of both fundamental and practical importance. The technique can be used flexibly to study porous electrode materials of high surface area, to which many surface techniques are not applicable. Therefore, Raman spectroscopy is among the most promising methods for use in electrochemistry. The major disadvantage of Raman spectroscopy is its very low detection sensitivity. However, surface-enhancedRaman scattering (SERS) can improve the sensitivity significantly by several orders of magnitude for roughened surfaces of many metals including noble and transition metals. This chapter will first introduce some fundamental background and features of electrochemical surface-enhanced Raman scattering (EC-SERS), followed by a detailed description of the experimental setup for electrochemical Raman spectroscopy and preparation of SERS substrates. The emphasis will be on how to obtain reliable information of very sensitive bio-related systems. Some examples, varying from amodelmolecule of benzene to real biomolecules, such as dopamine, NADH, DNA and cytochrome c (cyt c), will be shown to demonstrate how to apply EC-SERS for bio-related application. Finally, prospects and further developments of EC-SERS application in bio-related systems will be discussed.

Surface-Enhanced Raman Spectroscopic Study on the Co-adsorption of DNA Bases with Perchlorate

Abstract: National Natural Science Foundation of China [20673086, 20620130427, 20825313]; Natural Science Foundation of Fujian Province, China [2009J05032]

4,4'-dimercaprol azobenzene and preparation method thereof

Abstract: The invention discloses 4,4'-dimercaprol azobenzene and a preparation method thereof and relates to an azo sulfhydryl compound. The molecular formula of the 4,4'-dimercaprol azobenzene is HS(C6H4)N=N(C6H4)SH. The method comprises the following steps of: dissolving aniline into an aqueous sodium bicarbonate solution; adding I2 for reacting, then decompressing and pumping off the solvent to obtain 4-m-iodoaniline; dissolving the 4-m-iodoaniline into glacial acetic acid, adding NaBO3-4H2O and H3BOs for reacting, and then recrystallizing by using THF (Tetrahydrofuran) to obtain 4,4'-azobenzene diiodide; dissolving the 4,4'-azobenzene diiodide into the THF, adding an obtained mixed solution to magnesium chips in batches, and then cooling to obtain an azobenzene Grignard reagent; adding solid sulphur powder to the azobenzene Grignard reagent in batches and heating for reacting to obtain a vulcanized product; cooling and then adding an NH4Cl solution; acidizing by using hydrochloric acid andextracting through dichloromethane; combining organic phases, drying and filtering; decompressing to evaporate out the solvent to obtain a crude product; and extracting by using alcohol, and evaporating the solvent to dryness to obtain a product.

Electromagnetic Coupling Effect for Surface-enhanced Raman Spectroscopy and Tip-enhanced Raman Spectroscopy

Abstract: Electromagnetic Coupling between nanoparticles and that between tip and substrate are vitally important to surface-enhanced Raman spectroscopy and tip-enhanced Raman spectroscopy and their applications. We first demonstrate the coupling effects of the nanoparticles in the presence and absence of metallic substrates. The transfer of the hot spots from between the nanoparticles occurs when the substrate was changed from glass to Au thin film and with enhanced signal intensity. It gives indication for experimental design to achieve higher detection sensitivity. We used the model to investigate the molecules trapped in the nanoparticles and substrate to screen for the spectral properties of molecules in the molecular junction. When the nanoparticles were substituted by a tip, it becomes a very important system in tip-enhanced Raman spectroscopy. We systematically investigate the effect of tip and substrate distance on the enhancement both experimentally and theoretically. We found that when we compare the experimental result with the theoretical result, we have to consider very carefully the real distance between the tip and substrate and the height of molecule should not be neglected. When we further approach the tip to substrate by STM, it naturally forms the metal tip-molecule-metal substrate molecular junctions. We can use STM to probe the electronic properties of the molecules, and use TERS to investigate the structural properties of the molecular junction. We therefore construct a fishing-mode TERS method to simultaneously obtain chemical and conductance information for understanding the molecular junctions.

Fishing-Mode Tip-enhanced Raman Spectroscopy (FM-TERS) for Studying Single-Molecule Junctions

Abstract: State Key Laboratory of Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China bren@xmu.edu.cn Molecular electronics that uses molecules with unique functions as the basic units has attracted increasing interest in recent years. Various methods have been established to construct molecular transport junctions and characterise the various properties of the active region. Spectroscopic methods appear to be the most valuable techniques. Surface-enhanced Raman spectroscopy (SERS) with a single-molecule sensitivity has been used for characterizing the molecular junction. However, it was still suffered from the interference of molecules surrounding the molecular junction.

Structures and their influence factors of three-dimensional fractal cadmium layer formed by electrodeposition

Abstract: Three-dimensional fractal structure of the electrodeposited cadmium layer was investigated. The results suggested that the fractal growth begin with nanometer scale aggregate within which the atoms arrange in hexagonal close-packed lattice (the normal cadmium lattice). The fractal structure is correlated to the current density. The higher the current density is, the larger the size of fractal growth will be. Fractal structures can emerge in both the complete diffusion-limited process and the combination-limited process of the electrochemical reaction and diffusion. The fractal structure obtained from the simple hydrated ion electrolyte is different from that obtained from the complex ion electrolyte, which indicates they grow in different modes. The fractal dimensionality of deposit from the simple hydrated ion electrolyte is 2.592, smaller than that (2.608) from the complex ion electrolyte.

Scanning electrochemical microscopy - development of instrumentation utilizing piezo-bimorph x-y scanners

Abstract: The development of the instrumentation of a scanning electrochemical microscopy (SECM) is presented. The core of the SECM sensing system is constructed based on piezo-bimorph scanners, a mechanical micropositioner of multi-dimensional adjustment and ultramicroelectrodes. The control of the electrochemical cell and the SECM system is realized by a battery powered bipoteniostat and analog control circuits respectively with the control of a microcomputer work station. The demonstrations of SECM experiments are given on both a standard IDA sample and a silver electrode. Discussions on the resolution and quality of SECM image are made.