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Surface-Enhanced Raman Spectroscopy (SERS): General Introduction
Abstract
Surface-enhanced Raman scattering (SERS) was discovered in the mid-1970s, by which the intrinsically low detection sensitivity of Raman spectroscopy is no longer a fatal disadvantage for this analytical tool. As a general introduction of SERS, the almost 40-year history of SERS is first overviewed, showing that SERS has gone through a tortuous pathway to develop into a powerful diagnostic technique. We then describe the principle of SERS and enhancement mechanisms, illustrating that SERS is mainly surface plasmon resonance (SPR)- and nanostructure-enhancement phenomenon. The SERS measurement procedures, in particular the preparation of various SERS active substrates, are discussed. On the basis of four important criteria in analytical science, i.e. detection sensitivity, (energetic, spatial, and temporal) resolution, generality, and reliability, we highlight two different approaches to utilize the strength and offset the weakness of SERS. With the enormously high sensitivity and spectral resolution, SERS has been applied successfully to surface analysis and trace analysis by gaining meaningful information from an extremely small quantity of species even down to single molecules. To significantly improve the surface generality and spatial resolution, tip-enhanced Raman spectroscopy (TERS) was invented in 2000. To greatly improve the material generality and measurement reliability, shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) was introduced in 2010. Finally, prospective developments of SERS in substrates, methods, and theory are briefly discussed.Keywords: SERS ; TERS ; SHINERS ;surface plasmon; Raman Spectroscopy
... (2), where ε 0 and ε(ω) represents the permittivity of vacuum and metal, respectively. The resonant oscillation emerges when ε(ω) + 2ε m → 0, resulting in ˛ → ∞, thus termed as the localized surface plasmon resonance (LSPR) [32,33]. ...
... Besides, alkali metals (Li, Na, K, Rb, and Cs) and Al can also work as plasmonic materials in the UV region. Ga, In, Pt, Rh, their alloys, and some semiconductive materials such as TiN have also been explored as plasmonic materials [33]. ...
... Besides the EM enhancement based on the LSPR effect, there are other forms of enhancements in SERS, which are generally grouped as "chemical" enhancement [33]. Despite that the chemical enhancements (of the order of 10-10 3 ) are significantly smaller than the EM contributions, it significantly affects the pattern of the SERS spectra (in the frequency shift and relative intensity of the spectral bands). ...
Among photothermal, photovoltaic and photochemical techniques, photochemistry is superior in energy storage and transportation by converting photons into chemical fuels. Recently plasmonic photocatalysis, based on localized surface plasmon resonance (LSPR) generated from noble metal nanostructures, has attracted much attention. It promotes photochemical reaction efficiency by optimizing the solar spectrum absorption and the surface reaction kinetics. The deeper understanding is in urgent need for the development of novel plasmonic photocatalysts. Surface-enhanced Raman spectroscopy (SERS), which is also originated from the LSPR effect, provides an excellent opportunity to probe and monitor plasmonic photoreactions in situ and in real-time, with a very high surface sensitivity and energy resolution. Here, fundamentals of plasmonic photocatalysis and SERS are first presented based on their connections to the LSPR effect. Following by a validity analysis, latest studies of SERS applied for the plasmon mediated photochemical reaction are reviewed, focusing on the reaction kinetics and mechanism exploration. Finally, limitations of the present study, as well as the future research directions, are briefly analyzed and discussed.
... Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive technique capable of detecting trace amounts of substances for use in a variety of fields, including environmental monitoring, food safety, and life sciences [1,2]. Previous reports have shown that SERS originates from the inelastic light scattering of analyte molecules on the surface of metal nanostructures [3][4][5]. The enhancement of SERS involves two main mechanisms: electromagnetic enhancement (EM) and chemical enhancement (CM). ...
... The enhancement of SERS involves two main mechanisms: electromagnetic enhancement (EM) and chemical enhancement (CM). EM results from localized surface plasmon resonances (LSPR) which leads to significant SERS enhancement [3,[5][6][7]. CM is the result of charge transfer between metal nanoparticles and the molecules of the analyte [6,[8][9][10]. The two mechanisms can not be separated clearly but they work together to produce the overall SERS effect. ...
... Moreover, both the advantages and disadvantages of SERS are clear. The main disadvantages derive from its inherent lack of reliability and universality [150]. ...
... In life science, cell monitoring and optical physics. [148,150] 6 CET A higher efficiency in a wide wavelength range, a larger Stokes shift, the easier detection of the final acceptor, etc. ...
Over the past several years, resonance energy transfer involving noble metallic nanoparticles has received considerable attention. The aim of this review is to cover advances in resonance energy transfer, widely exploited in biological structures and dynamics. Due to the presence of surface plasmons, strong surface plasmon resonance absorption and local electric field enhancement are generated near noble metallic nanoparticles, and the resulting energy transfer shows potential applications in microlasers, quantum information storage devices and micro-/nanoprocessing. In this review, we present the basic principle of the characteristics of noble metallic nanoparticles, as well as the representative progress in resonance energy transfer involving noble metallic nanoparticles, such as fluorescence resonance energy transfer, nanometal surface energy transfer, plasmon-induced resonance energy transfer, metal-enhanced fluorescence, surface-enhanced Raman scattering and cascade energy transfer. We end this review with an outlook on the development and applications of the transfer process. This will offer theoretical guidance for further optical methods in distance distribution analysis and microscopic detection.
... The maximum enhancement of the incident field intensity at the nanoparticle surface can be obtained using it [8]. This can be understood as follows: As reported, electromagnetic field enhancement in SERS is a two-step process [46,47]. As shown in Fig. (8) in the first step, enhancement of local electromagnetic field takes place around the plasmonic nanoparticles (NPs), at ω 0 , the incident frequency (as also discussed in section 2.2.1.1). ...
... Zhu et al., 2021). But, the technology used in these researches has been severely limited as a quantitative analytical method due to its lack of reproducibility, generality, and reliability (Ding, Zhang, You, Ren, & Tian, 2020). It is important to point out that in the analysis by SERS, sample preparation is required that could not be suitable for in situ and fast monitoring of pesticide residues in tea plants. ...
Pesticide residue in tea is always known as a major concern in the process of tea quality assessment, as it poses potential risks to health even at very low levels. To explore the best approach for quantitative detection of pesticide residue in tea, electronic nose (e-nose) and confocal Raman microspectroscopy (CRM) were applied to prove their capability in the determination of chlorpyrifos concentration. Partial least square (PLS) regression was developed based on the e-nose and spectral variables separately and the fusion of the variables into a single array, to analyze the performance of the variable selection algorithms and use the complementary data acquired by e-nose and CRM sensing technologies. Support vector machine (SVM) and artificial neural network (ANN) models were then developed to the individual datasets and the fused dataset, to correlate the signals obtained by both technologies, with the concentration of pesticide residues measured in samples by reference analytical method. The detection model developed based on the data fusion outperformed those based on e-nose and CRM separately, and the result showed that both technologies had a major role in predicting the contamination of pesticide residue. The best prediction performance was derived with 32 effective variables selected from the fusion dataset by the ANN model, with the optimum value of RMSEP (0.0135) and R2p value of 0.973. This research demonstrated the high potential to combine e-nose and CRM data as an alternative approach for determining pesticide residues in tea processing, especially coupled with efficient chemometric strategies.
... Silver and gold nanostructures are the most widely used materials in SERS substrates due to their surface plasmon resonance (LSPR) properties, which cover a wide wavelength range in the visible and near-infrared regions where most Raman measurements are made [1,11]. Several methods have been developed for the fabrication of these substrates, which follow one of two gen- [10,12]. The top-down strategy is based on micro-and nanofabrication techniques (electron beam lithography [13], atomic layer deposition [14], focused ion beam [15] nanosphere lithography [16]). ...
The optimization of the geometrical properties of gold/silver nanoparticle arrangements to maximize their surface-enhanced Raman scattering (SERS) efficiency is studied in this work. For this purpose, the metallic nanostructures were created by thermally annealing gold and silver thin film layers deposited onto glass substrates. The SERS capabilities of the samples were evaluated by measuring an analyte solution of benzophenone with three different excitation laser wavelengths. Systematic investigations were carried out on different gold and silver nanoisland samples to determine how the SERS enhancement depends on the geometrical (particle diameter, interparticle distance) and optical parameters (plasmon wavelength) of the nanostructures, as well as on the wavelength of laser excitation. The importance of matching the excitation wavelength with the resonant plasmon absorbance properties of the surface was proved. However, it was also shown that the optimization of the geometrical properties of the nanoisland arrangements dominates over the selection of the excitation wavelength. A generalized exponential relationship between the SERS enhancement and the non-dimensional interparticle distance/particle diameter ratio was established. Optimal technological parameters for the fabrication of gold/silver nanoisland SERS substrates were proposed.
... SERS is a rapid technique, and it only takes minutes and sometimes just seconds to make the measurements. The availability of portable, handheld Raman devices makes point-of-care (onsite) measurements possible and practical [5]. ...
In this study, a new technique was developed to create an eco-friendly and biodegradable SERS sensor platform using electrospun corn zein fibers. First, electrospinning was used in conjunction with glutaraldehyde, a crosslinker for proteins, to create crosslinked zein nanofibers. The surface of the nanofibers was then decorated with 20-nm-diameter gold nanoparticles, and the biosensor platform was tested with the Raman active Rhodamine 6G. The high surface area and the high surface roughness enabled a SERS signal enhancement of 1.06 × 10⁶, which only required 2.8 × 10⁻⁷ g of gold nanoparticle deposition on the fibers. This electrospun zein-based gold nanoparticle-decorated sensor platform is not only made with a quicker, simpler and an inexpensive method compared to the other techniques requiring etching procedures and has a very good shelf life stability, but also serves as a green alternative to the plastic-based SERS sensor platforms with an equivalent and sometimes lesser SERS signal enhancement.
... The plasmon polaritons can generate a giant electromagnetic field at the metal surface. SERS can exploit this physical phenomenon to detect the Raman scattering of molecules located on the AuNP surface even at concentrations as low as picomoles 32 . Over the past two decades, 4-MBA SAM on metal nanosubstrates have been intensely explored because this molecule can readily conjugate to gold substrates and its surface plasmon enhanced Raman scattering is strong and depends on the pH of the surrounding nanoenvironment. ...
Regulation of intracellular pH is critically important for many cellular functions. The quantification of proton extrusion in different types of cells and physiological conditions is pivotal to fully elucidate the mechanisms of pH homeostasis. Here we show the use of gold nanoparticles (AuNP) to create a high spatial resolution sensor for measuring extracellular pH in proximity of the cell membrane. We tested the sensor in HepG2 liver cancer cells and MKN28 gastric cancer cells before and after inhibition of Na+/H+ exchanger. The gold surface conjugation strategy is conceived with a twofold purpose: i) to attach the AuNP to the membrane proteins and ii) to quantify the local pH from AuNP using surface enhanced Raman spectroscopy (SERS). The nanometer size of the cell membrane anchored sensor and the use of SERS enable us to visualize highly localized variation of pH induced by H+ extrusion, which is particularly upregulated in cancer cells.
... In addition, the necessary addition of a fluorescently active label may alter the structure or functionality of the targeted biomolecule. Label-free techniques, such as Raman microscopy, (2) can be used, but their sensitivity is typically orders lower compared to fluorescence. The fluo- rescence super-resolution techniques (3) that have been developed in the past decade improve resolution with an order of magnitude, but this typically comes at the expense of capability to image dynamics. ...
Correlation between light, mostly fluorescence, and electron microscopy (EM) is needed to identify biological molecules within their ultrastructural context and/or to relate the ultrastructure to preceding dynamics of biological molecules. Recent development of labels, sample preparation techniques, and microscopy tools allow researchers to bridge the gap between these two modalities, while dedicated, integrated microscopes merge the two techniques into one. This not only allows broader possibilities for implementation of CLEM (correlative light and electron microscopy) in analytical sciences but also enables novel applications crossing boundaries between the traditional microscopes. We provide an overview of the different CLEM approaches, including common labels and sample preparation techniques, and focus attention specifically on the advanced instrumentation and the novel opportunities and challenges these bring for the chemical and biological sciences.
... This discovery was the starting point of the now well established and widely used SERS. (13)(14)(15)(16) As indicated in Equation (1), the Raman intensity is proportional to the square of both the molecular polarizability and the incident electromagnetic laser field (l ∝ E 2 0 ), thus revealing that the metal nanostructure can alter either parameter as the basis of the augmented spectroscopic signals. For molecules in direct contact with the metal substrate, adsorption-induced modification of the polarizability may arise as a result of metal/molecule charge transfer processes and surface chemistry in general. ...
Surface-enhanced Raman spectroscopy (SERS) is a very powerful vibrational method that can be applied to a variety of biological samples provided that drawbacks, such as poor reproducibility of the signal and biocompatibility of the substrates, can be satisfactorily overcome. SERS is characterized by very low limits of detection, mainly due to the electromagnetic enhancement of the Raman signals, capable of achieving the single-molecule level. Moreover, the spectra of small molecules represent authentic molecular fingerprints with very narrow linewidths that, along with the additional enhancement and inter-/intramolecular selectivity gained through resonant laser excitation (surface-enhanced resonance Raman spectroscopy, SERRS), make this technique particularly suited for multiplexing applications in complex biological samples. In this article, we introduce first the physical principles of SER(R)RS and describe the different types of substrates, as well as the basic modern instrumentation. We then provide an overview of recent biological applications, including biophysical mechanistic and structural studies on isolated biomolecules, their direct and indirect detection, chemical imaging of biological samples, and biomedical applications. Finally, we briefly discuss our outlook for the future research in this field.
... Surface-Enhanced Raman Scattering (SERS) spectroscopy is an attractive tool for the detection of organic contaminants with high specificity and sensitivity, simple pretreatment of samples and rapid analysis time [1][2][3][4][5] . It is essential to improve the performance of SERS-active substrate [6,7]. Till now, so many reports have been demonstrated the significance of enhanced Raman signal induced by various noble metals structures [8,9]. ...
... Raman signal can be significantly enhanced by virtue of the surface-enhance Raman scattering (SERS) effect [6][7][8][9][10]. This is primarily a phenomenon associated with the amplification of Raman signals of analytes adsorbed on or very close to the nanostructures with free-electron metal (i.e., gold, silver and copper) and dielectric interfaces by several orders of magnitude due to the enhanced local electromagnetic (EM) fields and the enhanced scattering efficiency generated by surface-plasmon resonance (SPR) [11,12]. ...
Surface-enhanced Raman spectroscopy (SERS) was discovered in the mid-1970s and the development of SERS is parallel with the nanoscience, and in particular, SERS benefited considerably from new techniques for the preparation and characterization of SERS-active nanoparticles or nanostructures. SERS activity is closely related to the optical resonance property of the coinage metal nanomaterials, which can greatly enhance the local electromagnetic field, largely due to the excitation of surface plasmon resonance. In this article, we first generally review the development of SERS, and then the principles of SERS, followed by the preparation methods of SERS-active substrates and the strategies to expand the generality in SERS. In the “borrowing” SERS activity strategies, from coating transition metal onto SERS-active nanostructures, to tip-enhanced Raman spectroscopy (TERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), enormous efforts have been dedicated to overcoming the long-standing limitations of material and surface generalities in traditional SERS in the past decades. In the final section, we present a perspective with emphasis on the exploration of new nanomaterials suitable for the applications of SERS in a wider spectral region, as well as the design of new nanostructures to probe weakly SERS-active or SERS-inactive substrates.
In the real world, analytes usually exist in complex systems, and this makes direct detection by surface-enhanced Raman spectroscopy (SERS) difficult. Thin layer chromatography tandem with SERS (TLC-SERS) has many advantages in analysis such as separation effect, instant speed, simple process, and low cost. Therefore, the TLC-SERS has great potential for detecting analytes in mixtures without sample pretreatment. The review demonstrates TLC-SERS applications in diverse analytical relevant topics such as environmental pollutants, illegal additives, pesticide residues, toxic ingredients, biological molecules, and chemical substances. Important properties such as stationary phase, separation efficiency, and sensitivity are discussed. In addition, future perspectives for improving the efficiency of TLC-SERS in real sample detecting are outlined.
In its complexity, light-matter interaction has a proven value for many scientific fields, such as quantum mechanics, material sciences and spectroscopy. In recent decades, bioanalytical tools have been developed, taking advantage of this knowledge. Sensing techniques such as the ones depending on (bio) catalytic reactions could be improved in terms of sensitivity and limits of detection and quantification with light stimuli. Others, such as surface plasmon resonance (SPR), could only thrive after the unraveling of some light-matter interaction particularities. In addition, the consolidation of nanoscience, including the capability to synthesize nanoparticles with enzyme-like activity and selectivity (nanozymes), led to a new perspective on the practical advantages of designed materials with optical attributes deriving from subwavelength-scaled particles. A set of techniques could benefit from this phenomenon. Examples are Surface-Enhanced Raman Spectroscopy (SERS), derived from the Raman effect, and Localized Surface Plasmon Resonance (LSPR), derived from SPR. This chapter is an overview of light-matter interaction from the perspective of bioanalytical tools, highlighting the state of the art of plasmonic-based electrochemical and electroanalytical methods, taking advantage of designed nanoparticles with controlled size, geometry and composition.KeywordsBioanalytical methodsElectroanalytical methodsLSPRNanozymesPlasmonicsSERSSPR
Surface-enhanced Raman spectroscopy using functionalised nanoparticles or nano-engineered surfaces provides a highly selective and sensitive technique for detecting and quantifying analyte binding. However, practical diagnostic and sensing applications are hindered by technical variability due to hot-spotting and analyte drift, as well as variability in sample preparation and substrate uniformity. In this work, we introduce a novel joint experimental design and computational analysis procedure to minimize and/or control for these sources of error. Sample variability is minimized by preparing functionalised nanoparticles with and without analyte under the same conditions, and then recording and analysing difference spectra. To account for technical variability, multiple spectra are recorded from each sample. The key novelty of our analysis procedure is that all information about sample and technical variability is retained through to the final comparative analysis step, and we apply principal component analysis twice - once to extract “variance-minimized” spectra as principal loading vectors and again to distinguish between samples with and without the target analyte. Proof of principle experiments using thiolated aptamers to detect CoV-SARS-2 spike protein reveal that analyte binding show that analyte binding primarily shows up as a depletion of free covalent stretching bands, coupled to appearance of corresponding hydrogen-bonded stretching bands. This is quite different from previous work which largely focusses on changes in the “fingerprint” region where we find that the signal may be obscured by greater technical variability. Our computational analysis code can be freely downloaded from https://github.com/dlc62/DeltaPCA.
The nanochemical routes introduced in recent years have delivered important tools for the preparation of multifunctional nanomaterials with the potential to be used in a variety of applications. With the knowledge currently available, it is possible to prepare a wide array of inorganic nanoparticles (NPs) with well-defined average size, shape, surface chemistry or functionality. In particular, the ability to tailor the physicochemical properties of materials at the nanoscale has provided breakthroughs in sensing applications, such as in the development of new analytical protocols based on plasmonics. Metal NPs and their hybrid structures with the capability to enhance the Raman signal of molecular adsorbates have proved to be useful in the analysis of chemical species at low concentrations. The current review provides a timely overview of the literature regarding the use of dendrimers for the preparation of metal-based nanostructures. Moreover, the review also approaches recent research on multifunctional hybrids that integrate magnetic NPs and emphasizes their importance to fabricate magneto plasmonic materials for surface-enhanced Raman scattering (SERS). These developments are relevant for the design of sensing systems with great importance for biomedicine, catalysis, and environmental monitoring.
The book provides the readers of various discipline an easy understanding of the latest biophysical techniques pertaining to microbiology. Biofilm associated chronic infection is a major health problem and a serious concern to doctors, scientists and other health workers as it develops antibiotic and multi-drug resistance. This book describes various protocols utilized in the detection of the biofilm. The book has been divided into six sub sections which provides pertinent information about the various biophysical techniques and instruments that are used for detecting and analyzing the biofilm formation upon biotic and abiotic surfaces. The readers will be able to identify the techniques that can best cater information to solve the problem at hand. This book attempts to compile the latest information on the recent advances in the various functional aspects of microbial biofilms, their pathogenesis, present day treatments as well as detection strategies.
This book is meant for researchers in the field of microbiology and interested in understanding microbial pathogenesis, quorum sensing and biofilm formation.
Microbes tend to exist in polymicrobial communities embedded in a matrix of several compounds produced by themselves such as polysaccharides, proteins, extracellular nucleic acids, such as DNA or RNA, humic substances, signalling molecules, etc. These matrices are known as biofilms. Biofilm formations are triggered in hostile conditions to up-regulate nutrient sequestration and promote adherence and survival that makes them an interesting point of study over the years. Microbial biofilms play vital roles in quorum sensing, protection from antimicrobial agents, stress and even predators. Biofilm forming bacteria have been proven to be more efficient in plant growth promoting activities and survival in harsh environmental conditions that challenge colonization.
In the context of functional genomics, the field of metabolomics is becoming immensely important. At present day condition, “omics” data play a pivotal role in investigation of the metabolome that is actually the important part in systems biology. Apart from the investigations of biofluid from the cells and tissues from plants and animals, determination of microbial metabolomics has also been an area of high focus. The innovative development that has taken place in informatics and analytical technologies and the integration of various orthogonal approaches help in analysis of metabolites at the systems level biology. The microbial systems possess the inherent ability of converting from planktonic to sessile forms and remain attached to a solid surface encompasses by extracellular polymeric substances (EPS) and pilli. Theses EPS possess the framework with components like polysaccharides, proteins, nucleic acids, and various other minerals that not only provide nourishment to the developing sessile communities but also render antibiotic resistance among the organisms. The analysis of the various metabolic processes, inherent sensitivity of metabolomics and subtle change of the various biological pathways help in determining the growth and the expression of virulence that is crucial for the development of pathogenesis within the biofilm. The popularly used analytical technique in assessing the metabolomics includes liquid and gas chromatography associated with the mass spectrometry (LC-MS/HPLC/GC-MS) and spectroscopic approach like that of NMR. The representations of the metabolome data provide the information about the physiological status of the organisms. This chapter focuses on the concept of biofilm and the detection of the metabolomics associated with the formation of biofilm by HPLC/LC-MS and GC-MS taking reference of the biofilm formed by S. aureus.
It is known that biofilm acts as a defence mechanism for bacteria against an array of antimicrobials making it resistant causing antimicrobial resistance. Antimicrobial resistance is a global threat which needs to be tackled effectively. Since biofilm formation has an active role in this phenomenon it becomes pertinent to study its various aspects. This chapter deals with the various genes present in gram-positive and gram-negative bacteria responsible for biofilm formation. The relationship between biofilm, virulence and antimicrobial resistance has been dealt with extensively. Just knowing about the role of biofilm does not suffice our need, but the methods for its detection are very important. Therefore detection by Polymerase Chain Reaction (PCR) and Real-Time Polymerase Chain Reaction (RT-PCR) has been discussed in great length. There are various advantages as well as limitations to any technique, so is the case with the techniques mentioned above which is also mentioned in this chapter.
Bacterial adhesion on to the various biotic or abiotic surfaces and subsequent biofilm formation paves the path of microbial contamination in various clinical and industrial environments. The mode of biofilm formation and propagation depends on various factors such as availability of nutrient sources, ambient environmental conditions such as temperature, pH, salinity, and coping with the presence of various antimicrobials of the surroundings. Biofilm formation is a cell density dependent signaling mechanism under extreme stress conditions for survival of microorganisms. They consist of proteins, nucleic acids, polysaccharides, and lipids that are constantly being exchanged between the neighboring bacterial cells enclosed within a matrix of extracellular polymeric substances (EPS). The mechanism of bacteria–surface interaction can be best described by the advancements of microscopic techniques. This chapter will focus on the recent developments on the diverse and powerful tools such as atomic force microscopy (AFM) and surface probe microscopy (SPM) for understanding the nanoscale adhesive forces dominating the behavior and structure of biofilms and shedding light on the biofilm control strategies within clinical and industrial environments. These newer visualization techniques allow us with the opportunities of observing topographical landscape of bacterial cells through image heights, resolved structures of surface macromolecules, nanomechanical properties of microbial adhesion forces, and mode of receptor–ligand interaction (antibiofilm compounds) at the biofilm interface.
Bioimaging and biosensing have garnered interest in early cancer diagnosis due to the ability of gaining in-depth insights into cellular functions and providing a wide range of diagnostic parameters. Emerging 2D materials of multielement MXenes and monoelement black phosphorous nanosheets (BPNSs) with unique intrinsic physicochemical properties such as a tunable bandgap and layer-dependent fluorescence, high carrier mobility and transport anisotropy, efficient fluorescence quenching capability, desirable light absorption and thermoelastic properties, and excellent biocompatibility and biosafety properties provide promising nano-platforms for bioimaging and biosensing applications. In view of the growing attention on the rising stars of the post-graphene age in the progress of bioimaging and biosensing, and their common feature characteristics as well as complementarity for constructing complexes, the main objective of this review is to reveal the recent advances in the design of MXene or BPNS based nanoplatforms in the field of bioimaging and biosensing. The preparation and surface functionalization methods, biosafety, and other important aspects of bioimaging and biosensing applications of MXenes and BPNSs have been assessed systematically, along with highlighting the main challenges in further biomedical application. The review not only focuses on the advancements in 2D materials for use in bioimaging and biosensing but also assesses the possibility of their future potential in bioapplications.
Surface-enhanced Raman spectroscopy (SERS) and related spectroscopies are powered primarily by the concentration of the electromagnetic (EM) fields associated with light in or near appropriately nanostructured electrically-conducting materials, most prominently, but not exclusively high-conductivity metals such as silver and gold. This field concentration takes place on account of the excitation of surface-plasmon (SP) resonances in the nanostructured conductor. Optimizing nanostructures for SERS, therefore, implies optimizing the ability of plasmonic nanostructures to concentrate EM optical fields at locations where molecules of interest reside, and to enhance the radiation efficiency of the oscillating dipoles associated with these molecules and nanostructures. This review summarizes the development of theories over the past four decades pertinent to SERS, especially those contributing to our current understanding of SP-related SERS. Special emphasis is given to the salient strategies and theoretical approaches for optimizing nanostructures with hotspots as efficient EM near-field concentrating and far-field radiating substrates for SERS. A simple model is described in terms of which the upper limit of the SERS enhancement can be estimated. Several experimental strategies that may allow one to approach, or possibly exceed this limit, such as cascading the enhancement of the local and radiated EM field by the multiscale EM coupling of hierarchical structures, and generating hotspots by hybridizing an antenna mode with a plasmonic waveguide cavity mode, which would result in an increased local field enhancement, are discussed. Aiming to significantly broaden the application of SERS to other fields, and especially to material science, we consider hybrid structures of plasmonic nanostructures and other material phases and strategies for producing strong local EM fields at desired locations in such hybrid structures. In this vein, we consider some of the numerical strategies for simulating the optical properties and consequential SERS performance of particle-on-substrate systems that might guide the design of SERS-active systems. Finally, some current theoretical attempts are briefly discussed for unifying EM and non-EM contribution to SERS.
As a crucial structural parameter, shell thickness greatly influences the optical properties of metallic nanoshells. However, there still lacks a reliable approach to prepare ultrathin core-shell nanoparticles. To solve this problem, a two-step gold seeding process was pointed out to increase the packing density of gold seeds on the silica core. By using this method, the packing density of gold seeds reaches ~60%, enabling us to successfully reduce the shell thickness to sub-10 nm range. Afterwards, we investigated optical properties of the as-prepared ultrathin nanoshells. It is found that thinner nanoshells exhibit a wider optical tunability and a greater electromagnetic field enhancement than their thicker counterparts, which makes ultrathin nanoshells an ideal substrate for surface enhanced spectroscopes.
The Langmuir-Blodgett (LB) technique has been used to obtain spatially resolved surface-enhanced resonance Raman scattering (SERRS) spectra of single dye molecules dispersed in the matrix of a fatty acid. The experimental results presented here mimic the original electrochemical surface-enhanced Raman scattering (SERS) work where the background bulk water did not interfere with the detection of the SERS signal of molecules adsorbed onto the rough silver electrode. LB monolayers of the dye in fatty acid have been fabricated on silver island films with a concentration, in average, of one probe molecule per micrometer square. The properties of single-molecule spectroscopy were investigated using micro-Raman including mapping and global images. Blinking of the SERRS signal was also observed.
We present a theory to explain the anomalous enhancement of light scattering from molecules adsorbed at a metal-solution interface. It is found that tunneling of electrons between a surface molecule and the metal induces a resonance at a point in the vicinity of the Fermi surface. A dynamical equilibrium due to photoionization and recombination stabilizes the system near resonance.
A comprehensive development of the charge‐transfer theory of surface enhanced Raman scattering (SERS) is presented. We incorporate the Herzberg–Teller mixing of zero‐order Born–Oppenheimer electronic states by means of vibronic interaction terms in the Hamiltonian. This is similar to the theory of Tang and Albrecht12 except that we include metal states as part of a molecule–metal system. When this is done we may no longer discard a term involving mixing of ground‐state vibrations. The theory is comprehensive in that both molecule‐to‐metal and metal‐to‐molecule transfer is considered. Furthermore, both Franck–Condon and Herzberg–Teller contributions to the intensity are obtained. The former, however, contribute only to the intensity of totally symmetric vibrations, while the latter contribute to nontotally symmetric vibrations as well. Since overtones are observed in SERS only weakly if at all, the Herzberg–Teller terms are most consistent with experimental findings. The resulting formulas may be interpreted as a type of resonance Raman effect in which intensity for the charge transfer transitions is borrowed from an allowed molecular transition. We may also carry out the sum over metal states. This procedure predicts a logarithmic resonance at the Fermi level of the metal. We thus predict intensity vs voltage profiles such as I ∝ ‖ln(ωFI−ω+iΓ)‖2 which fits the experimental curves quite well.
Covering everything from the basic theoretical and practical knowledge to new exciting developments in the field with a focus on analytical and life science applications, this monograph shows how to apply surface-enhanced Raman scattering (SERS) for solving real world problems.
The optical properties of metallic nanostructures are particularly important for the field of nanoscience and technology. Excitation of the localized surface plasmon resonance (LSPR) of metallic surfaces having nanoscale features results in local electro magnetic (EM) field enhancement, which dramatically increases the signal observed from molecules adsorbed to the surface of plasmonic nanostructures. This chapter focuses on a technique that takes advantage of this effect, namely surface-enhanced Raman spectroscopy (SERS). We first introduce the physical basis of the LSPR, with particular attention to the dielectric function of plasmonic materials as it relates to nanoparticle extinction. Next, we focus on the relationships among LSPR, EM enhancement, and SERS - highlighting both fundamental and applied experiments. Finally, we turn our attention to the future of SERS, including studies involving new materials, nanostructures, and techniques.
Considered one of the major fields of photonics of the beginning 21st century, plasmonics offers the potential to confine and guide light below the diffraction limit and promises a new generation of highly miniaturized photonic devices. Offering both a comprehensive introduction to the field and an extensive overview of the current state of the art, "Plasmonics: Fundamentals and Applications" should be of great value to the newcomer and to the experienced researcher.
The first part of the book describes the fundamentals of this research area, starting with a review of Maxwell’s equations in a form suited to the description of metals. Subsequent chapters introduce the two major ingredients of plasmonics, surface plasmon polaritons at metallic interfaces and localized plasmons in nanostructures. The mathematics of their description, excitation and imaging of the modes are discussed. This part closes with a presentation of electromagnetic surface waves at lower frequencies in the THz and microwave regime, comprising both spoof or designer plasmons and surface phonon polaritons.
Building on the fundamentals, the second part discusses some of the most prominent applications of plasmons: Plasmon waveguides, extraordinary transmission through aperture arrays, sensing and surface enhanced Raman scattering, spectroscopy as well as metamaterials. Exemplary studies in each of these fields taken from the original literature are presented.
Various roughening procedures for the bare Zn electrode such as chemical etching, electrochemical deposition and the electrochemical oxidation-reduction method were tried to obtain surface-enhanced Raman spectroscopy (SERS) from it and electrochemical oxidation-reduction method was proved effectively. Two electrochemical oxidation-reduction methods were described. One is linear sweep oxidation-reduction cycles (ORC) and the other is a double-step ORC. By using confocal Raman microscopy, surface enhanced Raman spectra of pyridine adsorbed on the bare roughened Zn electrodes were observed for the first time, when reduction potential was controlled at -1.6 V and oxidation potential at -0.7 V.
In the Comment by Domke and Pettinger [Phys. Rev. B 75, 236401 (2007)] on our study on "Scanning-probe Raman spectroscopy with single-molecule sensitivity" the authors raise concerns whether our tip-enhanced Raman response is due to carbon clusters as molecular decomposition products of the malachite green molecules used. Their arguments are based on the different spectral characteristics we observe between the tip-enhanced and far-field Raman response. Here, we show the results of systematic control experiments to support the conclusions drawn by Neacsu that all spectral features can be related to malachite green molecules. Comparing Raman spectra for different degrees of near-field enhancement, the absence of spectral changes during bleaching, examining a broad spectral range, and the explicit comparison with Raman signals from carbon impurities validates our original assignment, including the single-molecule response.
Surface-Enhanced Raman Scattering (SERS) was discovered in the 1970s and has since grown enormously in breadth, depth, and understanding. One of the major characteristics of SERS is its interdisciplinary nature: it lies at the boundary between physics, chemistry, colloid science, plasmonics, nanotechnology, and biology. By their very nature, it is impossible to find a textbook that will summarize the principles needed for SERS of these rather dissimilar and disconnected topics. Although a basic understanding of these topics is necessary for research projects in SERS with all its many aspects and applications, they are seldom touched upon as a coherent unit during most undergraduate studies in physics or chemistry. This book intends to fill this existing gap in the literature. It provides an overview of the underlying principles of SERS, from the fundamental understanding of the effect to its potential applications. It is aimed primarily at newcomers to the field, graduate student, researcher or scientist, attracted by the many applications of SERS and plasmonics or its basic science. The emphasis is on concepts and background material for SERS, such as Raman spectroscopy, the physics of plasmons, or colloid science, all of them introduced within the context of SERS, and from where the more specialised literature can be followed. * Represents one of very few books fully dedicated to the topic of surface-enhanced Raman spectroscopy (SERS) * Gives a comprehensive summary of the underlying physical concepts around SERS * Provides a detailed analysis of plasmons and plasmonics. "Besides an overview of current promising research topics, this book is a self-contained introduction to Raman spectroscopy and fluorescence that summarises the main concepts and ideas needed for SERS. It is also a self-contained introduction to the physics of plasmon resonances within the broader scope of plasmonics. A detailed presentation of the SERS electromagnetic model and its extension to surface-enhanced fluorescence is included." "Aimed primarily at newcomers to the field, graduate students, and other researchers or scientists attracted by the many possible applications of SERS and plasmonics, or their basic science."--BOOK JACKET.
Surface Enhanced Vibrational Spectroscopy (SEVS) has reached maturity as an analytical technique, but until now there has been no single work that describes the theory and experiments of SEVS. This book combines the two important techniques of surface-enhanced Raman scattering (SERS) and surface-enhanced infrared (SEIR) into one text that serves as the definitive resource on SEVS. Discusses both the theory and the applications of SEVS and provides an up-to-date study of the state of the art. Offers interpretations of SEVS spectra for practicing analysts. Discusses interpretation of SEVS spectra, which can often be very different to the non-enhanced spectrum - aids the practicing analyst.
Fiber enhanced Raman sensing is presented for versatile and extremely sensitive analysis of pharmaceutical drugs and biogenic gases. Elaborated micro-structured optical fibers guide the light with very low losses within their hollow core and provide at the same time a miniaturized sample container for the analytes. Thus, fiber enhanced Raman spectroscopy (FERS) allows for chemically selective detection of minimal sample amounts with high sensitivity. Two examples are presented in this contribution: (i) the detection of picomolar concentrations of pharmaceutical drugs; and (ii) the analysis of biogenic gases within a complex mixture of gases with analytical sensitivities in the ppm range.
An accurate but simple method for determining electromagnetic fields near the surfaces of small metal spheroidal particles has been used to determine field and Raman enhancements for 10 metals in groups 1, 11, 12, and 13. This method corrects the simple small particle LaPlace electrostatic field for electrodynamic depolarization and damping effects to give a result which is equivalent to solving Maxwell's equations to order k3 (k = 2π/λ), and it also incorporates size-dependent plasmon broadening effects which arise from small particle surface scattering of the conduction electrons. With this method we have studied the dependence of both field and Raman enhancement factors on particle size and shape, and from this we have determined optimal sizes, shapes, excitation frequencies, and enhancement factors for each metal. Comparisons with experiment are given where possible. Our results for the noble metals are in accord with the observed frequency dependence of SERS for Ag, Au, and Cu, but the optimized peak enhancements are still well below (factor of 101-102) experimental enhancement estimates. Enhancements for the alkalis are comparable to those for the noble metals, but with a flatter dependence on frequency in the visible region, and with different optimum particle sizes and shapes. Al and In are found to give large enhancements over a broad region of the spectrum (IR → UV) but Ga only gives large enhancements in the IR. The size and shape dependences of the enhancements for the group 13 metals show great variation with metal and with frequency. Cd is found to exhibit relatively small electromagnetic enhancements in the visible and near-UV regions, while Zn has windows of significant enhancement at 2.5 and 3.5 eV.
In recent years, research in electrochemistry has turned increasingly to the combination of data obtained by conventional electrochemical techniques with results derived using a range of ex situ and in situ surface analytical methods(1) (see Table 1). The major reason for this development is that electrochemical techniques inevitably measure the sum of all the processes at the interfaces and, moreover, cannot characterize the molecular species present so that structural information can only be inferred indirectly. In situ methods have a special role to play in this search for molecular specificity, as they are able to characterize the nature and structure of both the electrode and solution sides of the interface; by contrast, ex situ methods can only give information about strongly adsorbed species. In turn, vibrational spectroscopy has a special role among these in situ methods, as vibrational spectra can be used to “finger print” the species present while changes in the spectra of the “telltale” species give information about changes in structure and of the molecular environment of these species.
IntroductionLab-on-a-chip TechnologyMicrofluidic Platforms and Application for SERSSummaryReferences
The field of nanoparticle research has drawn much attention in the past decade as a result of the search for new materials. Size confinement results in new electronic and optical properties, possibly suitable for many electronic and optoelectronic applications. A characteristic feature of noble metal nanoparticles is the strong color of their colloidal solutions, which is caused by the surface plasmon absorption. This article describes our studies of the properties of the surface plasmon absorption in metal nanoparticles that range in size between 10 and 100 nm. The effects of size, shape, and composition on the plasmon absorption maximum and its bandwidth are discussed. Furthermore, the optical response of the surface plasmon absorption due to excitation with femtosecond laser pulses allowed us to follow the electron dynamics (electron−electron and electron−phonon scattering) in these metal nanoparticles. It is found that the electron−phonon relaxation processes in nanoparticles, which are smaller than the electron mean free path, are independent of their size or shape. Intense laser heating of the electrons in these particles is also found to cause a shape transformation (photoisomerization of the rods into spheres or fragmentation), which depends on the laser pulse energy and pulse width.
We report for the first time the tip-enhancement of resonance Raman scattering using deep ultraviolet (DUV) excitation wavelength. The tip-enhancement was successfully demonstrated with an aluminum-coated silicon tip that acts as a plasmonic material in DUV wavelengths. Both the crystal violet and adenine molecules, which were used as test samples, show electronic resonance at the 266-nm excitation used in the experiments. With results demonstrated here, molecular analysis and imaging with nanoscale spatial resolution in DUV resonance Raman spectroscopy can be realized using the tip-enhancement effect. Copyright © 2009 John Wiley & Sons, Ltd.
Metamaterials (MMs) are artificial, engineered materials with rationally designed compositions and arrangements of nanostructured building blocks. These materials can be tailored for almost any application because of their extraordinary response to electromagnetic, acoustic, and thermal waves that transcends the properties of natural materials (1–3). The astonishing MM-based designs and demonstrations range from a negative index of refraction, focusing and imaging with sub-wavelength resolution, invisibility cloaks, and optical black holes to nanoscale optics, data processing, and quantum information applications (3). Metals have traditionally been the material of choice for the building blocks, but they suffer from high resistive losses—even metals with the highest conductivities, silver and gold, exhibit excessive losses at optical frequencies that restrict the development of devices in this frequency range. The development of new materials for low-loss MM components and telecommunication devices is therefore required.
Shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) based on Au@SiO2 or Au@Al2O3 nanoparticles (NPs) shows great potential to break the long-standing limitations of substrate and surface generality of surface-enhanced Raman scattering (SERS). However, the shell of SiO2 or Al2O3 can easily be dissolved in alkaline media, which limits the applications of SHINERS in alkaline systems. Besides that, the synthesis of Au@SiO2 NPs can be further simplified and Au@Al2O3 NPs be replaced by other NPs that are more amenable for mass production. In an attempt to make SHINERS NPs available in any systems practically, we report the synthesis of ultrathin and compact Au@MnO2 NPs. The shell thickness of MnO2 can be controlled down to about 1.2 nm without any pinhole. SHINERS based on such Au@MnO2 NPs exhibits much higher Raman enhancement effect than Au@SiO2 NPs and can be applied in alkaline systems in which Au@SiO2 or Au@Al2O3 NPs cannot be applied. Copyright © 2011 John Wiley & Sons, Ltd.
Benzotriazole (BTAH) is well known as an effective corrosion inhibitor for Cu because of its ability to make a coordination polymer film on the surface that provides a barrier to Cu oxidation. BTA− film formation was investigated on single-crystal and polycrystalline Cu surfaces with shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) using silica-encapsulated Au nanoparticles. Potential-dependent spectra display reversible film formation on polycrystalline Cu and irreversible film formation on single-crystal Cu. Grain boundaries leading to smaller BTA−-Cu oligomers are proposed to be the reason for cathodic degradation of the BTA− polymeric films on polycrystalline Cu. Copyright © 2011 John Wiley & Sons, Ltd.
In 1978 it was discovered, largely through the work of Fleischmann, Van Duyne, Creighton, and their coworkers that molecules adsorbed on specially prepared silver surfaces produce a Raman spectrum that is at times a millionfold more intense than expected. This effect was dubbed surface-enhanced Raman scattering (SERS). Since then the effect has been demonstrated with many molecules and with a number of metals, including Cu, Ag, Au, Li, Na, K, In, Pt, and Rh. In addition, related phenomena such as surface-enhanced second-harmonic generation, four-wave mixing, absorption, and fluorescence have been observed. Although not all fine points of the enhancement mechanism have been clarified, the majority view is that the largest contributor to the intensity amplification results from the electric field enhancement that occurs in the vicinity of small, interacting metal particles that are illuminated with light resonant or near resonant with the localized surface-plasmon frequency of the metal structure. Small in this context is gauged in relation to the wavelength of light. The special preparations required to produce the effect, which include among other techniques electrochemical oxidation-reduction cycling, deposition of metal on very cold substrates, and the generation of metal-island films and colloids, is now understood to be necessary as a means of producing surfaces with appropriate electromagnetic resonances that may couple to electromagnetic fields either by generating rough films (as in the case of the former two examples) or by placing small metal particles in close proximity to one another (as in the case of the latter two). For molecules chemisorbed on SERS-active surface there exists a "chemical enhancement" in addition to the electromagnetic effect. Although difficult to measure accurately, the magnitude of this effect rarely exceeds a factor of 10 and is best thought to arise from the modification of the Raman polarizability tensor of the adsorbate resulting from the formation of a complex between the adsorbate and the metal. Rather than an enhancement mechanism, the chemical effect is more logically to be regarded as a change in the nature and identity of the adsorbate.
Using a general formulation we show that by using surface electromagnetic waves in an attenuated-total-reflection prism configuration it should be possible to enhance the intensity of Raman scattering by a thin overlayer on a Ag surface by two orders of magnitude and that the use of surface electromagnetic waves may in fact make it possible to observe coherent anti-Stokes Raman scattering by the overlayer.
Surface enhanced Raman spectroscopy (SERS) leverages the specificity of Raman scattering and the sensitivity provided by localized plasmonic effects for applications in chemical and biomolecular detection. However, nearly four decades after the first report of SERS, practical uses of the technique remain limited. Optofluidic SERS—the synergistic use of microfluidics to improve the performance of SERS—may finally lead to practical devices for chemical and biomolecular detection. In this review, we describe recent advances in optofluidic SERS microsystems that have been developed to improve the performance and applicability of SERS. These techniques include designs that improve the light–analyte interaction, that perform active or passive concentration of metal nanoparticles and/or analyte molecules, and that utilize microfluidic techniques to improve functionality. In addition, we present optofluidic SERS techniques that enable new applications that have not been possible before the advent of optofluidics. Finally, we project future advances in optofluidic SERS and present a vision for the disruptive technologies that will enable the translation of SERS from the research lab to practical uses.
The SER spectra of 4-, 3- and 2-cyanopyridines adsorbed on a silver electrode are presented. The results show that cyanopyridines may adsorb in two different orientations, end-on (with the N atom of the Py ring bound to the surface) and flat, and that for potentials more negative than −1.1 V (SCE), the cyanopyridine radical anions can also be detected. The SERS intensity vs. potential curves show more than one potential of maximum SERS intensity which are assigned to the existence of more than one species on the electrode surface. The analytical potentially of SERS on electrodes has also been investigated. It is shown that the relative SERS intensity (νCN of the 4-CNPy (2120 cm−)/breathing mode of Py (1008 cm−1)), at a fixed Py bulk concentration and at a fixed potential and exciting radiation, depends linearly on the 4-CNPy bulk concentration in the range 10−7-10−5M. The selectivity of the technique has also been investigated by studying the SER spectrum and the SERS intensity vs. potential curves for a mixture of 10−3M 4-CNPy, pyridine (Py) and 4-methylpyridine(4-MePy) in 0.1 M KCl aqueous solution.
The interaction of light with clusters and random distributions of metal hemispheroids on a perfect conducting flat surface is studied. Significant SERS enhancements are found to arise from multiple plasmon contributions to the surface electromagnetic fields.
We present an introduction to surface-enhanced Raman scattering (SERS) which reviews the basic experimental facts and the essential features of the mechanisms which have been proposed to account for the observations. We then review very recent fundamental developments which include: SERS from single particles and single molecules; SERS from fractal clusters and surfaces; and new insights into the chemical enhancement mechanism of SERS.
We use a theory, previously developed by us, to investigate numerically the properties of the light scattered by a molecule adsorbed near a solid surface. We illustrate how the angular dependence and the polarization of the scattered light can be used to infer, in certain limiting cases, the position of the molecule with respect to the surface. The frequency dependence of the scattered radiation is investigated and possible causes for the observed enhancement of scattering by a metallic surface are discussed.
Studies of surface-enhanced Raman scattering from pyridine adsorbed on Ag surfaces in ultrahigh vacuum show a strong dependence on both surface roughness and pyridine coverage. The observation of enhancement (104) for physisorbed pyridine multilayers in addition to the first molecular layer implies that the enhanced effect is electromagnetic rather than chemical in origin.
Electrodynamic calculations of the electric field on the surface of large Ag prolate spheroids indicate that the field enhancement decreases rapidly, the resonance shifts to longer wavelengths and broadens, and a new set of higher-order resonances appears at shorter wavelengths. These results form the basis for comparison with surface-enhanced Raman scattering measurements from lithographically produced Ag microstructures.
Measurements of the characteristic electron energy loss spectra of aluminum and magnesium were made (in a reflection experiment) during oxidation of a fresh evaporated layer of either metal. It was found that surface oxidation results in the rapid disappearance of the low-lying energy losses (10.3 ev in aluminum and 7.1 ev in magnesium) and the appearance of modified low-lying losses of 7.1 ev in aluminum and 4.9 ev in magnesium. The general changes in the loss spectra and the particular changes in the spectrum of aluminum were in good agreement with the predictions of Ferrell and Stern.
An indicator molecule, para-nitrosodimethylanaline (p-NDMA), has been used to study the chemical nature of surface complexes involving the active site for SERS in the electrochemical environment. We present evidence for positively charged Ag atoms stabilized by coadsorbed Cl− ions as the primary sites which are produced during the oxidation reduction cycle treatment of an Ag electrode. Depending on the relative number of Cl− ions which influence the Ag site the active site demonstrates a greater or lesser electron accepting character toward p-NDMA. This character is influenced by the applied voltage and by the presence of Tl+ ions in the bulk of the solution near the surface. As in previously studied systems p-NDMA/Cl−/Ag complexes demonstrate charge transfer excitation which in this case is from the p-NDMA to the Ag site. These results further solidify the importance of complex formation in electrochemical SERS and suggest that caution should be applied when using SERS as a quantitative measure of surface coverage.
Cross sections for Rayleigh and Mie scattering on a roughned conducting surface are given. The Rayleigh scattering is strongly enhanced by roughness. Rayleigh and Mie scattering are found to interfere with each other. The experimental consequences for surface enhanced Raman Scattering (SERS) are discussed. (AIP)
A model for Raman scattering from molecules chemisorbed on surfaces is proposed. We suggest that part of the enhancement is due to modulation of the metal-surface reflectivity by the motion of the atom binding the molecule to the surface. The parameters entering the model are easily estimated from a jellium model of the solid. One quantitative comparison with existing experimental data is made.
On increasing the wavelength of excitation over the range 350–700 nm, Raman bands of pyridine adsorbed at a roughened silver electrode are found to increase in intensity, relative to bands of the bulk medium (aqueous perchlorate or liquid pyridine) in contact with the electrode. The increase is observed in the bands at 1000–1050 cm−1 and 1600 cm−1 due to ring stretching, and similar increases are observed in other bands of the surface species, notably those due to CH stretching (3076 cm−1), b2 ring deformation (669 cm−1, and AgN stretching (239 cm−1, which have not been reported previously.
The excitation energy dependence of the surface enhanced Raman scattering of adsorbed molecules is calculated based on the effective resonance model for a molecule–metal system. As a consequence of the effective resonant Raman process of the adsorbed molecule, a remarkable departure from an ω4 law is obtained near the excitation energies which satisfy the resonant condition. The significance of the substrate metal on the degree of the enhancement is discussed with the use of a result that the position of the effective resonant level is closely connected with that of the Fermi level. A comparison with the recent experimental results on the excitation profiles is also made.
Intense Raman scattering by pyridine molecules adsorbed on silver or gold aqueous sol particles of dimensions comparable to the wavelength is reported. The degree of intensity enhancement is strongly dependent on the excitation wavelength, with a sharp resonance Raman maximum for excitation at the wavelength of the Mie extinction maximum of the metal particles, and for the silver sols the Raman maximum is shown to follow the extinction maximum to longer wavelengths with increase in particle size. A new resonance Raman phenomenon is thus proposed which is the Raman component of resonant Mie scattering, and in which the polarizability of the metal particles is modulated by the vibrations of the adsorbed molecules. These observations confirm that surface plasma oscillations are involved in the intense Raman scattering already reported for molecules adsorbed at roughened silver surfaces. The metal dielectric function requirements for resonant Mie scattering enable the optimum excitation wavelength for plasma resonance-enhanced Raman studies at the surface of other metals to be estimated.
The Raman spectra of electrochemically deposited Hg2Cl2, Hg2Br2 and HgO on Hg/Pt substrates have been observed.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.