In-situ surface-enhanced Raman scattering and FT-Raman spectroscopy of black prints

The black inkjet and laser prints were analysed with regard to application in forensic analysis of questioned documents. The purpose of this work was to study spectral properties and compare the suitability of surface-enhanced Raman scattering (SERS) with Fourier transform Raman spectra of prints. This work aimed to find optimal surface-enhanced Raman spectroscopic approach for the future analysis of documents using statistical methods. In this work, we analysed eight prints of four laser and four inkjet devices. The samples were measured using two dispersive Raman devices; (DXR Raman microscope with excitation line 532 nm, Foram 685-2 spectrometer − 685 nm) and FT-Raman device (Bruker Spectrometer MultiRAM with excitation line 1064 nm). The silver nanoparticles (AgNPs) colloid for SERS experiment were synthesised and checked by UV–vis spectroscopy and scanning electron microscopy (SEM). The remarkable differences caused by centrifugation of silver colloid were observed just in the SEM images. The main contribution of this paper is to propose the novel approach achieving sufficient SERS signal intensity of black prints using the both, laser and inkjet printers. Moreover, this method is based on just a single metal colloid, and the analysis can be performed in-situ, i.e. directly on the printed sample surface. We consider the SERS could by highly promising and universal for applications in the forensic analysis of printed documents with the combination of statistical method when conventional methods are not effective.     

In-situ monitoring of the curing of epoxy resins by Raman spectroscopy

Polymerization reactions are based on complex processes that are somewhat difficult to predict via mathematical models, especially without experimental data. A method to investigate the cure of epoxies via in-situ Raman spectroscopy has been developed.Differential Scanning Calorimetry (DSC) is the industry-standard method for determining the cure of a polymer, but it is a labor-intensive method that is also fairly slow. Raman spectroscopy was used to monitor the cure chemistry of DGEBA (Diglycidyl Ether of Bisphenol A) and to observe in-situ the evolution of the reticulation.     

Quantitative surface-enhanced Raman spectroscopy

The purpose of this tutorial review is to show how surface-enhanced Raman (SERS) and resonance Raman (SERRS) spectroscopy have evolved to the stage where they can be used as a quantitative analytical technique. SER(R)S has enormous potential for a range of applications where high sensitivity needs to be combined with good discrimination between molecular targets, particularly since low cost, compact spectrometers can read the high signal levels that SER(R)S typically provides. These advantages over conventional Raman measurements come at the cost of increased complexity and this review discusses the factors that need to be controlled to generate stable and reproducible SER(R)S calibrations.     

Detection of bacteria by surface-enhanced Raman spectroscopy

The detection and identification of dilute bacterial samples by surface-enhanced Raman spectroscopy has been explored by mixing aqueous suspensions of bacteria with a suspension of nanocolloidal silver particles. An estimate of the detection limit of E. coli was obtained by varying the concentration of bacteria. By correcting the Raman spectra for the broad librational OH band of water, reproducible spectra were obtained for E. coli concentrations as low as approximately 10³ cfu/mL. To aid in the assignment of Raman bands, spectra for E. coli in D₂O are also reported. Figure Light scattering apparatus used to detect bacteria     

Wavelength-scanned surface-enhanced Raman excitation spectroscopy

A detailed wavelength-scanned surface-enhanced Raman excitation spectroscopy (WS SERES) study of benzenethiol adsorbed on Ag nanoparticle arrays, fabricated by nanosphere lithography (NSL), is presented. These NSL-derived Ag nanoparticle array surfaces are both structurally well-characterized and extremely uniform in size. The WS SERES spectra are correlated, both spatially and spectrally, with the corresponding localized surface plasmon resonance (LSPR) spectra of the nanoparticle arrays. The surface-enhanced Raman scattering (SERS) spectra were measured in two excitation wavelength ranges: (1) 425-505 nm, and (2) 610-800 nm, as well as with the 532-nm line from a solid-state diode-pumped laser. The WS SERES spectra have line shapes similar to those of the LSPR spectra. The maximum SERS enhancement factor is shown to occur for excitation wavelengths that are blue-shifted with respect to the LSPR lambda(max) of adsorbate-covered nanoparticle arrays. Three vibrational modes of benzenethiol (1575, 1081, and 1009 cm(-1)) are studied simultaneously on one substrate, and it is demonstrated that the smaller Raman shifted peak shows a maximum enhancement closer to the LSPR lambda(max) than that of a larger Raman shifted peak. This is in agreement with the predictions of the electromagnetic (EM) enhancement mechanism of SERS. Enhancement factors of up to approximately 10(8) are achieved, which is also in good agreement with our previous SERES studies.     

Intercalator-DNA interactions revealed by NIR surface-enhanced Raman spectroscopy

Using 1064 nm excited surface-enhanced Raman spectroscopy (SERS) a well known intercalator, ethidium bromide (EB), and a structurally related compound, 4-methyl-2,7-diamino-5,10-diphenyl-4,9-diazapyrenium hydrogensulfate (ADAP), have been studied. Concentration dependent SERS spectra of both aromatic species (1 × 10⁻⁷-5 × 10⁻⁵ M) indicated existence of dimeric associates at high concentration and an equilibrium shift towards monomers with a concentration decrease. Interactions of the intercalating molecules with DNA have been studied for various intercalator/DNA (base pair) molar ratios ranging from 10/1 to 1/10. In colloidal samples containing an intercalator in excess relative to DNA binding sites (from 10/1 to 2/1) enhancement of the Raman scattering gradually weakened, indicating a decrease in a number of free molecules adsorbed on the metal surface due to binding with DNA. At the drug/DNA ratios of 1/2 and 1/5 weaker but observable SERS bands indicated insertion of the drug molecules between the base pairs (intercalation strongly diminished interaction of the drug molecules with metal surface) as well as non-intercalative binding of the drug molecules able to stay in closer contact with a metal surface. A total intercalation of EB and ADAP molecules (intercalator/DNA of 1/7 and 1/10) resulted in almost complete loss of the SERS signal. Intensity of the SERS spectra of the intercalator/DNA complexes relative to the SERS intensity of the free intercalating molecules diminished to a lesser degree for ADAP/DNA than for EB/DNA. The obtained difference was attributed to a larger aromatic surface of the ADAP molecules which, although intercalated, could be positioned near the enhancing nanoparticles, unlike the smaller EB molecules which were deeply inserted within the DNA helix.     

Bioaerosol detection and characterization by surface-enhanced Raman spectroscopy

Instrumentation has been developed to detect and characterize airborne pollen and bacteria rapidly by injecting a bioaerosol into a nanocolloidal suspension of silver particles using a micropump. The biological particles were mixed with the silver colloid in order to deposit the metallic particles on the surface of the bioanalyte. The silver/bioanalyte suspension was pumped through a light scattering cuvette, and the enhanced Raman spectrum was recorded. Surface-enhanced Raman spectra are presented for tree pollen (cottonwood and redwood pollen) and a bacterium (Escherichia coli), and the E. coli spectra are compared with results obtained from the literature and with results obtained previously by mixing various concentrations of the bioanalyte with the silver colloid. Although the system has not been optimized to maximize the Raman spectra, it is shown spectra can be obtained rapidly. Some assignments of the chemical bonds associated with the spectra are based on previously published results for bacteria and pollen.     

Electrochemical surface-enhanced Raman spectroscopy of nanostructures

This tutorial review first describes the early history of SERS as the first SERS spectra were obtained from an electrochemical cell, which led to the discovery of the SERS effect in mid-1970s. Up to date, over 500 papers have been published on various aspects of SERS from electrochemical systems. We then highlight important features of electrochemical SERS (EC-SERS). There are two distinctively different properties of electric fields, the electromagnetic field and static electrochemical field, co-existing in electrochemical systems with various nanostructures. Both chemical and physical enhancements can be influenced to some extent by applying an electrode potential, which makes EC-SERS one of the most complicated systems in SERS. Great efforts have been made to comprehensively understand SERS and analyze EC-SERS spectra on the basis of the chemical and physical enhancement mechanisms in order to provide meaningful information for revealing the mechanisms of electrochemical adsorption and reaction. The EC-SERS experiments and applications are then discussed from preparation of nanostructured electrodes to investigation of SERS mechanisms and from characterization of adsorption configuration to elucidation of electrochemical reaction mechanisms. Finally, prospective developments of EC-SERS in substrates, methods and theory are discussed.     

Rapid detection of an anthrax biomarker by surface-enhanced Raman spectroscopy

A rapid detection protocol suitable for use by first-responders to detect anthrax spores using a low-cost, battery-powered, portable Raman spectrometer has been developed. Bacillus subtilis spores, harmless simulants for Bacillus anthracis, were studied using surface-enhanced Raman spectroscopy (SERS) on silver film over nanosphere (AgFON) substrates. Calcium dipicolinate (CaDPA), a biomarker for bacillus spores, was efficiently extracted by sonication in nitric acid and rapidly detected by SERS. AgFON surfaces optimized for 750 nm laser excitation have been fabricated and characterized by UV-vis diffuse reflectance spectroscopy and SERS. The SERS signal from extracted CaDPA was measured over the spore concentration range of 10(-14)-10(-12) M to determine the saturation binding capacity of the AgFON surface and to calculate the adsorption constant (Kspore=1.7 x 10(13) M(-1)). At present, an 11 min procedure is capable of achieving a limit of detection (LOD) of approximately 2.6 x 10(3) spores, below the anthrax infectious dose of 10(4) spores. The data presented herein also demonstrate that the shelf life of prefabricated AgFON substrates can be as long as 40 days prior to use. Finally, these sensing capabilities have been successfully transitioned from a laboratory spectrometer to a field-portable instrument. Using this technology, 10(4) bacillus spores were detected with a 5 s data acquisition period on a 1 month old AgFON substrate. The speed and sensitivity of this SERS sensor indicate that this technology can be used as a viable option for the field analysis of potentially harmful environmental samples.     

Chemical analysis of polycyclic aromatic hydrocarbons by surface-enhanced Raman spectroscopy

The use of surface-enhanced Raman spectroscopy (SERS) for trace determination of polycyclic aromatic hydrocarbons (PAHs) is described. This paper focuses on the development of SERS-active substrates that are specific for the characterization and spectroscopic study of PAHs. The SERS-active substrates are based on thin gold films evaporated on a glass surface previously treated with a mercaptoalkylsilane. SERS of PAHs was investigated over uncoated gold island films and over such films coated with a self-assembled monolayer (SAM) of 1-propanethiol. Adsorption of PAHs on a plain SERS-active Au-film led to a surface-induced decomposition of PAHs, due to catalytic properties of nanostructured gold. Thus, the functionalization of the SERS-active substrates by means of SAM was done aiming at a specific chemical interaction toward PAHs. Thus, in addition to preventing decomposition of the PAHs, the coating also concentrates the hydrophobic PAHs close enough to the SERS-active interface. Results show that high sensitivity, SERS-active nanostructured gold substrates that show selectivity towards PAHs were obtained, with the following properties: strong intensification of the Raman signal, reproducibility, and stability over time. The employed methodology enables the observation of excellent Raman spectra of PAHs in aqueous environment at ppm levels.     

Monitoring the electrochemistry of single molecules by surface-enhanced Raman spectroscopy

Coherent control of chemical species in complex systems is always subject to intrinsic inhomogeneities from the environment. For example, slight chemical modifications can decisively affect transport properties of molecules on surfaces. Hence, single-molecule (SM) studies are the best solution to avoid these problems and to study diverse phenomena in biology, physics, and chemistry. Along these lines, monitoring SM redox processes has always been a "holy grail" in electrochemistry. To date, claims of SM electrochemistry by spectroscopy have come only from fluorescence quenching of polymers and redox-fluorescent molecules. In unconnected developments, the potential of the bianalyte surface-enhanced Raman scattering (SERS) method as a technique with SM sensitivity has been demonstrated. Raman spectroscopy has the potential to explore SM detection of any molecule, independent of its chemical nature. We provide definitive proof of SM events following redox cycles using SERS. The superior sensitivity and spectral richness of SERS makes it general enough to study, in principle, SM electron transfer of any (label-free) molecule.     

Differentiation of selected blue writing inks by surface-enhanced Raman spectroscopy

Raman spectroscopy and surface enhanced Raman spectroscopy were used to examine 14 blue inks obtained from commercially available stationery. Standard colouring agents in the inks: β-phase of phtalocyanine blue PB15 and some homologues of the methyl violet class, were identified. Surface enhanced Raman spectra were recorded on a firm heterostructure of silver/nanocrystalline diamond/silicon constituting an active substrate providing the possibility to write directly on the surface. Based on the differences in traditional and surface enhanced Raman spectra, two inks were identified unambiguously, the remaining inks were categorised into three groups exhibiting common spectral features. Despite their similarity, surface enhanced Raman spectra exhibited soft variations enabling discrimination of the inks, thus proving the usefulness of the method.     

Coupled subwavelength gratings for surface-enhanced Raman spectroscopy

Dual subwavelength Ag gratings with a small gap of about 15 nm are demonstrated to provide a huge additional SERS enhancement, more than 10(3) fold in scattering efficiency over normal SERS on an Ag film due to the strong plasmon coupling, which is simulated by theoretical calculation. The simulation also shows the advantages of the coupled two-layer gratings over the one-layer grating for SERS measurement. Our study provides a promising and feasible way of structure design for extremely sensitive substrates of SERS.     

Towards single-microorganism detection using surface-enhanced Raman spectroscopy

The identification and discrimination of microorganisms is important not only for clinical reasons but also for pharmaceutical clean room production and food-processing technology. Vibrational spectroscopy such as IR, Raman, and surface-enhanced Raman scattering (SERS) can provide a rapid ‘fingerprint’ on the chemical structure of molecules and is used to obtain a ‘fingerprint’ from microorganisms as well. Because of the requirement that a single bacterium cell and noble metal nanoparticles must be in close contact and the lack of a significant physical support to hold nanoparticles around the single bacterium cell, the acquisition of SERS spectra for a single bacterium using colloidal nanoparticles could be a challenging task. The feasibility of SERS for identification down to a single bacterium is investigated. A Gram-negative bacterium, Escherichia coli, is chosen as a model for the investigation. Because the adsorption of silver nanoparticles onto the bacterial cell is an exclusive way for locating nanoparticles close to the bacterium cell, the absorption characteristics of silver nanoparticles with different surface charges are investigated. It is demonstrated that the citrate-reduced colloidal silver solution generates more reproducible SERS spectra. It is found that E. coli cells aggregate upon mixing with silver colloidal solution, and this may provide an additional benefit in locating the bacterial cell under a light microscope. It is also found that a laser wavelength in the UV region could be a better choice for the study due to the shallow penetration depth. It is finally shown that it is possible to obtain SERS spectra from a single cell down to a few bacterial cells, depending on the aggregation properties of bacterial cells for identification and discrimination.     

Real-time surface-enhanced Raman spectroscopy monitoring of surface pH during electrochemical melting of double-stranded DNA

The application of a negative potential ramp at a double-stranded DNA (dsDNA) functionalized electrode surface results in the gradual denaturation of the DNA in a process known as electrochemical melting. The underlying physical chemistry behind electrochemically driven DNA denaturation is not well understood, and one possible mechanism is a change in local pH at the electrode surface. We demonstrate that by coimmobilization of p-mercaptobenozic acid at a dsDNA-functionalized electrode surface, it is possible to monitor both DNA denaturation and the local pH simultaneously using surface-enhanced Raman spectroscopy. We find that the local pH at the electrode surface does not change as the applied potential is scanned negative and the dsDNA denatures. We therefore conclude that in these experiments electrochemical melting is not caused by electrochemically driven local pH changes.     

Rationally designed nanostructures for surface-enhanced Raman spectroscopy

Research on surface-enhanced Raman spectroscopy (SERS) is an area of intense interest because the technique allows one to probe small collections of, and in certain cases, individual molecules using relatively straightforward spectroscopic techniques and nanostructured substrates. Researchers in this area have attempted to develop many new technological innovations including high sensitivity chemical and biological detection systems, labeling schemes for authentication and tracking purposes, and dual scanning-probe/spectroscopic techniques that simultaneously provide topographical and spectroscopic information about an underlying surface or nanostructure. However, progress has been hampered by the inability of researchers to fabricate substrates with the high sensitivity, tunability, robustness, and reproducibility necessary for truly practical and successful SERS-based systems. These limitations have been due in part to a relative lack of control over the nanoscale features of Raman substrates that are responsible for the enhancement. With the advent of nanotechnology, new approaches are being developed to overcome these issues and produce substrates with higher sensitivity, stability, and reproducibility. This tutorial review focuses on recent progress in the design and fabrication of substrates for surface-enhanced Raman spectroscopy, with an emphasis on the influence of nanotechnology.     

Ultrasensitive detection of malondialdehyde with surface-enhanced Raman spectroscopy

Malondialdehyde (MDA) is a biomarker of lipid peroxidation that has been widely associated with food rancidity as well as many human diseases. Most current MDA detection methods involve MDA reaction with thiobarbituric acid (TBA), followed by UV-visible and/or fluorescence detection of high-performance liquid chromatography (HPLC)-separated TBA-MDA. Herein, we report the first proof-of-concept study of surface-enhanced Raman detection of a TBA-MDA adduct using silver nanoparticles as the SERS substrate and the 632.8 nm HeNe laser as a Raman excitation source. Current SERS detection limit of TBA-MDA is 0.45 nM, ~100 times higher than the 36 nM fluorescence sensitivity recently reported with the HPLC-purified TBA-MDA. Molecular specificity of the SERS technique was studied by comparing the SERS spectrum of TBA-MDA with those acquired with TBA adducts of other TBA-reactive compounds (TBARCs) that includes formaldehyde, acetaldehyde, butyraldehyde, trans-2-hexenal, and pyrimidine. Compared to TBA and TBA adducts with those TBARCs, the SERS activity of TBA-MDA adduct is significantly higher. The possibility of direct SERS detection of TBA-MDA in a reaction mixture (without HPLC separation) has also been investigated.     

Study on transport of molecules in gel by surface-enhanced Raman spectroscopy

Cellulose - Surface-enhanced Raman spectroscopy (SERS)-based biosensors have recently been extensively developed because of their high sensitivity and nondestructive nature. Conventional SERS...     

Detection of proteins on silica-silver core-shell substrates by surface-enhanced Raman spectroscopy

We have employed the proposed Silica-Silver Core-Shell (SSCS) SERS-active substrates to detect four model proteins: lysozyme (a protein without chromophore), cytochrome c (a protein with chromophore of heme), fluorescein isothiocyanate (FITC)-anti human IgG (labeled with FITC) and atto610-biotin/avidin (recognition with labeled small molecules). SERS spectra of these proteins and Raman labels on the SSCS substrates show both high sensitivity and reproducibility, which are due to electromagnetic SERS enhancement with additional localization field within closely packed Ag nanoparticles decorated on the SiO(2) nanoparticles and the aggregation of SiO(2)@Ag particles. We have found that the SERS intensities of atto610-biotin/avidin adsorbed on the SSCS substrates are about 20 times stronger than those from Ag plating on Au-decorated substrate. Moreover, the broad surface plasmon resonance (SPR) of the proposed substrates will extend SERS applications to more biological molecules with different laser excitations.     

基于超微电极的原位电化学拉曼光谱

原位电化学拉曼光谱是一种重要的光谱电化学技术.基于超微电极的原位电化学拉曼光谱将拉曼光谱反映的结构信息与电极表面的电化学过程从实验上严格对应和关联,为深刻理解电化学反应机理提供依据.本文综述了采用超微电极作为工作电极的原位电化学拉曼光谱的研究方法和应用进展,总结了应用超微电极作为工作电极开展电化学拉曼光谱实验的方法和具有表面增强拉曼活性的超微电极制备方法,展示了如何利用在超微电极表面获得的拉曼光谱与界面电化学过程的严格关联研究单个锌颗粒电化学氧化过程、吡啶分子在Au电极表面的电化学吸附过程,以及如何利用该技术能以高的信噪比和灵敏度同时测量光电流与分子反应这一特性研究对巯基苯胺选择性光氧化反应.采用超微电极作为工作电极的原位电化学拉曼光谱技术极大拓展了拉曼光谱技术的研究范围,有望成为探索(光)电化学反应的有力工具.