Modern Raman Spectroscopy: A Practical Approach
Abstract
This book reflects the dramatic increase in the number of Raman spectrometers being sold to and used by non-expert practitioners. It contains coverage of Resonance Raman and SERS, two hot areas of Raman, in a form suitable for the non-expert. Builds Raman theory up in stages without overloading the reader with complex theory. Includes two chapters on instrumentation and interpretation that shows how Raman spectra can be obtained and interpreted. Explains the potential of using Raman spectroscopy in a wide variety of applications. Includes detailed, but concise information and worked examples.
... Molecules already in their excited states may relax to their ground state, resulting in a higher frequency scattered light than the incoming radiation (anti-Stokes shift, Fig. 1). Both of these shifts can be probed by Raman spectroscopy (Smith & Dent, 2005). If the sample is excited by energy in the mid-infrared region of the spectrum, absorbing this energy will result in the transition from its ground vibrational state to the first excited state, forming the basis of FTIR spectroscopy ( Fig. 1) (Siebert & Hildebrandt, 2008;Smith & Dent, 2005). ...
... Both of these shifts can be probed by Raman spectroscopy (Smith & Dent, 2005). If the sample is excited by energy in the mid-infrared region of the spectrum, absorbing this energy will result in the transition from its ground vibrational state to the first excited state, forming the basis of FTIR spectroscopy ( Fig. 1) (Siebert & Hildebrandt, 2008;Smith & Dent, 2005). ...
... With the invention of lasers in the 1970s and the availability of high-sensitivity charge-coupled devices (CCDs) shorter acquisition times paved the way for real-time monitoring and "hyperspectral" Raman imaging (Dieing & Hollricher, 2008). Raman excitation frequencies can range from the ultraviolet (e.g., 270 nm) to visible (e.g., 532, 633 nm) to near infrared (e.g., 785, 1064 nm) and influence Raman signal intensity (Smith & Dent, 2005), resonance enhancement effects (e.g., carotenoids at 514 and 532 nm (Gill, Kilponen, & Rimai, 1970)), as well as sample degradation and autofluorescence of plant tissues (Prats- Mateu, Bock, Schroffenegger, Toca-Herrera, & Gierlinger, 2018). Together with the numerical aperture of the microscope objective, the laser wavelength determines the laser spot size and the spatial resolution in Raman imaging experiments (Lee, 2012). ...
Spectral imaging technologies simultaneously record spectral and spatial information about plant tissues in a noninvasive way. Differences in techniques result in different selection rules and spatial resolutions. This article introduces the basic principles of Raman, Fourier-transform Infrared (FTIR) and autofluorescence imaging and finally compares their strength and drawbacks. The methods result in spectral datasets as bases for image generation. Spectral preprocessing together with univariate and multivariate data analysis approaches are essential for informative lignin imaging and analysis and therefore also briefly illustrated and discussed. Examples of imaging lignin and other aromatic components in a broad range of plant tissues show the potential as well as the limitations of microspectroscopic imaging.
... Raman spectroscopy is an established method for characterizing the chemical composition of heterogenous materials. [1,2] Applications of non-destructive, in situ Raman microspectroscopy have resulted in rapid progress in understanding biomolecule fossilization and the detection of biosignatures based on comparative statistical analyses of fossil organic matter. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The in situ approach facilitates rapid non-destructive analysis of surface-cleaned samples without requiring time-consuming extractions of the organic matter that may alter fossil molecular compounds. ...
... Raman spectroscopy not only characterizes molecular functional groups (small molecular units with distinct chemical properties), but also provides insights into higher-level structural organization by detecting intermolecular and organo-mineral interactions. [1,2] The utility of in situ Raman microspectroscopy in iden-tifying general patterns in molecular and mineralogical composition, as well as bioinorganic interactions in composite materials, renders it an informative analytical tool. Raman scattering can be induced by excitation wavelengths ranging from ultraviolet to visible (VIS, e.g., green at 532 nm) to near-infrared. ...
... [19] These different laser wavelengths are characterized by different advantages and disadvantages. [1,2] A deep ultraviolet wavelength prevents overlap of Raman signals and fluorescence, but the high-energy laser readily causes heat damage to a sample. Near-infrared Raman applications, in contrast, operate at a low laser energy, and therefore yield substantially weaker signals. ...
A recent article argued that signals from conventional Raman spectroscopy of organic materials are overwhelmed by edge filter and fluorescence artefacts. The article targeted a subset of Raman spectroscopic investigations of fossil and modern organisms and has implications for the utility of conventional Raman spectroscopy in comparative tissue analytics. The inferences were based on circular reasoning centered around the unconventional analysis of spectra from just two samples, one modern, and one fossil. We validated the disputed signals with in situ Fourier-Transform Infrared (FT-IR) Spectroscopy and through replication with different lasers, filters, and operators in independent laboratories. Our Raman system employs a holographic notch filter which is not affected by edge filter or other artefacts. Multiple lines of evidence confirm that conventional Raman spectra of fossils contain biologically and geologically meaningful information. Statistical analyses of large Raman and FT-IR spectral data sets reveal patterns in fossil composition and yield valuable insights into the history of life.
... The first one (D-peak), between 1300 and 1450 cm −1 , is a characteristic scattering peak of graphitic structures. The second one (G-peak), between 1550 and 1650 cm −1 , is a consequence of lattice defects, disordered arrangement, and the low symmetry carbon structure of graphite [31], characteristic of aromatic rings and hetero rings, especially aromatic amines [32,33]. These two functional groups are the main components of the BCs. ...
... The first one (Dpeak), between 1300 and 1450 cm −1 , is a characteristic scattering peak of graphitic structures. The second one (G-peak), between 1550 and 1650 cm −1 , is a consequence of lattice defects, disordered arrangement, and the low symmetry carbon structure of graphite [31], characteristic of aromatic rings and hetero rings, especially aromatic amines [32,33]. These two functional groups are the main components of the BCs. ...
... The pH pzc values were obtained by the relation between the initial pH i and the variation of pH (pH f -pH i ) [33,36]. ...
In this work, Norway spruce bark was used as a precursor to prepare activated biochars (BCs) via chemical activation with potassium hydroxide (KOH) as a chemical activator. A Box-Behnken design (BBD) was conducted to evaluate and identify the optimal conditions to reach high specific surface area (SSA) and high mass yield BC samples. The studied BC preparation parameters and their levels were: pyrolysis temperature (700, 800, and 900 °C), holding time (1, 2, and 3 h), and the ratio of the biomass: chemical activator of 1: 1, 1.5, and 2. The planned BBD yielded BC with extremely high SSA values, up to 2209 m2.g-1. In addition, the BCs were physicochemically characterized, and the results indicated that the BCs exhibited disordered carbon structures and presented a high quantity of O-bearing functional groups on their surfaces, which might improve their adsorption performance towards organic pollutant removal. The BC with the highest SSA value was then employed as an adsorbent to remove Evans Blue dye (EB) and colorful effluents. The kinetic study followed a General Order (GO) as the most suitable model to describe the experimental data, while the Redlich-Peterson model fitted the equilibrium data better. The EB adsorption capacity was 396.1 mg.g-1. The employment of the BC in the treatment of synthetic effluents, with several dyes and other organic and inorganic compounds, returned a high percentage of removal degree up to 87.7%. Desorption and cyclability tests showed that the biochar can be efficiently regenerated maintaining an adsorption capacity of 75% after four adsorption-desorption cycles. The results of this work pointed out that Norway spruce bark indeed is an interesting precursor for producing biochars with very promising properties.
... First reported in 1928, Raman spectroscopy is the phenomenon of inelastic scattering of light at longer or shorter wavelengths than that of the incident source [1,2]. Because such changes in frequency are specific to a particular vibration within the molecule of interest, the composition of the sample can be determined in a non-destructive manner using Raman spectroscopy [3]. However, since only one in ~10 7 photons scatters inelastically, Raman spectroscopy is an inherently weak technology. ...
... SERS enhancement is attributed to two factors: electromagnetic enhancement and charge transfer. The former mechanism is dependent on an interaction between the localized surface plasmon resonance (LSPR) of the metallic nanoparticle surface and the adsorbed molecule [3]. When incident laser light interacts with the metallic nanoparticles (NPs), it induces an oscillation of conduction band electrons, which increases polarizability of the adsorbed molecule leading to significant enhancement of Raman scattering [5]. ...
... For biomedical applications, SERS nanoparticles (or SERS nanotags) typically consist of a plasmonic nanoparticle core coated with molecules (Raman reporters) that are encapsulated in a protective shell that can be decorated with targeting ligands (Figure 1a). Raman reporters are selected not only based on their polarizability and resonance properties but also their binding affinity to the metal NP surface, which increases the overall number of reporters per particle, therefore generating higher signal intensity [3,11,12]. The metal/molecule system is encapsulated in a biocompatible coating that stabilizes the metal nanoparticle and prevents desorption of the Raman reporter molecules from the NP's surface [13]. ...
Surface-enhanced Raman spectroscopy (SERS) nanotags hold a unique place among bioimaging contrast agents due to their fingerprint-like spectra, which provide one of the highest degrees of detection specificity. However, in order to achieve a sufficiently high signal intensity, targeting capabilities, and biocompatibility, all components of nanotags must be rationally designed and tailored to a specific application. Design parameters include fine-tuning the properties of the plasmonic core as well as optimizing the choice of Raman reporter molecule, surface coating, and targeting moieties for the intended application. This review introduces readers to the principles of SERS nanotag design and discusses both established and emerging protocols of their synthesis, with a specific focus on the construction of SERS nanotags in the context of bioimaging and theranostics.
... The light absorption leads to a transition of the molecule from its ground state to an excited state. In this case, the energy of the incident photon corresponds to the difference between energies of the ground and the excited states [28,34]. When the molecule relaxes from the excited to the ground state, a photon with the same energy is emitted. ...
... The photon interacts with the molecule and polarizes its electron cloud around the atomic nuclei with the formation of a short-lived "virtual" state. This state is unstable and the photon with a changed energy is re-radiated [34]. The scattered photon may have lower or higher energy than the incident photon. ...
... In the first case, which is called Stokes scattering, the molecule is transited from the ground vibrational state n to a "virtual" state with the absorption of energy and is promoted to an excited vibrational state m with a higher energy. In the second case, which is called anti-Stokes scattering, the molecule that is already in an excited state such as m due to the thermal fluctuations is transited to the ground state n ( Figure 3) [28,34]. Because the number of molecules that are in an excited vibrational state at room temperature is small, anti-Stokes scattering is weak as compared to Stokes scattering [34]. ...
Many envisaged applications, such as nanoelectronics, photovoltaics, thermoelectric power generation, light-emission devices, energy storage and biomedicine, necessitate single-walled carbon nanotube (SWCNT) samples with specific uniform electronic properties. The precise investigation of the electronic properties of filled SWCNTs on a qualitative and quantitative level is conducted by optical absorption spectroscopy, Raman spectroscopy, photoemission spectroscopy and X-ray absorption spectroscopy. This review is dedicated to the description of the spectroscopic methods for the analysis of the electronic properties of filled SWCNTs. The basic principle and main features of SWCNTs as well as signatures of doping-induced modifications of the spectra of filled SWCNTs are discussed.
... Raman spectroscopy measures a very weak effect of inelastic scattering that accompanies laser-induced excitation of molecules. The Raman effect is related to changes in the polarizability of molecules due to the vibration energies of functional groups [25], which results in a shift of the photon energies from the frequency of the excitation source. The major advantage of Raman spectroscopy is its ability to obtain a chemical fingerprint of a sample that contains fundamental frequencies from the mid-infrared range by means of visible and NIR light, which is transmitted by glass materials, and it has a higher energy and deeper penetration [25]. ...
... The Raman effect is related to changes in the polarizability of molecules due to the vibration energies of functional groups [25], which results in a shift of the photon energies from the frequency of the excitation source. The major advantage of Raman spectroscopy is its ability to obtain a chemical fingerprint of a sample that contains fundamental frequencies from the mid-infrared range by means of visible and NIR light, which is transmitted by glass materials, and it has a higher energy and deeper penetration [25]. ...
Optical spectroscopic analysis of the chemical composition of milk in its natural state is complicated by a complex colloidal structure, represented by differently sized fat and protein particles. The classical techniques of molecular spectroscopy in the visible, near-, and mid-infrared ranges carry only bulk chemical information about a sample, which usually undergoes a destructive preparation stage. The combination of Raman spectroscopy with confocal microscopy provides a unique opportunity to obtain a vibrational spectrum at any single point of the sample volume. In this study, scanning confocal Raman microscopy was applied for the first time to investigate the chemical microstructure of milk using samples of various compositions. The obtained hyperspectral images of selected planes in milk samples are represented by three-dimensional data arrays. Chemometric data analysis, in particular the method of multivariate curve resolution, has been used to extract the chemical information from complex partially overlaid spectral responses. The results obtained show the spatial distribution of the main chemical components, i.e., fat, protein, and lactose, in the milk samples under study using intuitive graphical maps. The proposed experimental and data analysis method can be used in an advanced chemical analysis of natural milk and products on its basis.
... At <250-nm operation, the target Raman and fluorescence response becomes spectrally separated, allowing samples to be analysed in detail. Furthermore, as the laser wavelength reduces below 250 nm it approaches the electronic transition of several organic molecules producing a resonant effect that can amplify the Raman signal by several orders of magnitude [4,5,6]. ...
... Current high performance deep UV instruments operating below 250 nm use gas pumped lasers [4,5], which must be water cooled and dry nitrogen purged, making them difficult to deploy in a manufacturing facility. It should be noted that lasers are available commercially operating at 257 and 261 nm which have been used for Raman observations. ...
Monoclonal antibodies and antibody fragments are increasingly important classes of biotherapeutics. However, these products are both challenging and expensive to manufacture. New Process Analytical Technologies (PAT) used to monitor these products during their manufacture are of significant interest. Deep UV Raman spectroscopy promises to provide the required specificity and accuracy, however instruments, have historically been large and complex. In this paper a new deep UV Raman instrument is described using a solid‐state laser and a spatial heterodyne spectrometer. The instrument overcomes practical limitations of the technique and could readily be used for online measurement. A series of observations have been made of biopharmaceutical products, including IgG and domain antibodies. Where high levels of both specificity and linearity when measuring samples of different concentration with a precision of better than 0.05 mg/ml has been demonstrated This article is protected by copyright. All rights reserved.
... Esparcimiento Inelástico: Aproximadamente 1 fotón de cada 10 7 del haz de luz incidente es esparcido con un corrimiento en frecuencia, el cuál es producto de las ondas acústicas que están presentes en el medio (Brillouin) o por las moléculas de la muestra bajo análisis que esparcen los fotones con menor (Raman Stokes)ó mayor (Raman Anti-Stokes) energía que los fotones incidentes [52,53]. ...
... El esparcimiento de luz resultante puede tener la misma frecuencia que el haz incidente (Esparcimiento Elástico), o bien, puede presentar un corrimiento en frecuencia ocasionado por la ganancia/pérdida de energía (Esparcimiento Inelástico), los cuáles sonúnicos para cada componente de la muestra. Esta representación de niveles de energía se puede observar de forma gráfica en el llamado Diagrama de Niveles [52]. ...
... In the last decades, Raman and FTIR instrumentations have been significantly improved by their coupling with optical microscopes that let perform the imaging analysis. In this way, by mapping micro-areas of interest, it is possible to combine the information derived from the morphological analysis of the sample with its punctual chemical composition [15,16]. However, given the different physical phenomena on which the two techniques rely, IR spectroscopy requires 5-10 μm-thick tissue sections for analysis in transmission mode [9,17,18], while RMS can be applied to solid and thicker samples. ...
... In addition, RMS provides maps with a better spatial resolution than FTIR, allowing the detection of biological modifications which cannot be highlighted using more traditional techniques [19]. In fact, while FTIR shows some limitations due to the diffraction limit, which restricts the achievable spatial resolution to 10-20 μm, the shorter wavelengths exploited by RMS yield a diffraction-limited spatial resolution of 1 μm or less, depending on the objective [3,15]. ...
Currently, various analytical techniques, including scanning electron microscopy, X-Ray diffraction, microcomputed tomography, and energy dispersive X-ray spectroscopy, are available to study the structural or elemental features of hard dental tissues. In contrast to these approaches, Raman Microspectroscopy (RMS) has the great advantage of simultaneously providing, at the same time and on the same sample, a morpho-chemical correlation between the microscopic information from the visual analysis of the sample and its chemical and macromolecular composition. Hence, RMS represents an innovative and non-invasive technique to study both inorganic and organic teeth components in vitro. The aim of this narrative review is to shed new light on the applicative potential of Raman Microspectroscopy in the dental field. Specific Raman markers representative of sound and pathological hard dental tissues will be discussed, and the future diagnostic application of this technique will be outlined. The objective and detailed information provided by this technique in terms of the structure and chemical/macromolecular components of sound and pathological hard dental tissues could be useful for improving knowledge of several dental pathologies. Scientific articles regarding RMS studies of human hard dental tissues were retrieved from the principal databases by following specific inclusion and exclusion criteria.
... The spectrum of the silicon substrate included just one peak related with the MB at 1626 cm −1 , which was attributed to the C-C ring stretch. Since the displacement is generally bigger on the ring systems in heavy molecules, the presence of the ring stretching peak on the silicon substrate's spectrum was expected [32]. This peak was also visible in the MB analysis on the plain gold surface. ...
... There were three peaks that could only be detected during the analysis with the optimized SERS substrate: 1033 cm −1 , 1299 cm −1 , and 1331 cm −1 . Since the deformation modes generally do not cause the creation of strong polarization changes, the Raman signals generated by them are generally weak [32]. The reason why these peaks could not be detected using a silicon or a plain gold substrate might be their weak Raman signal tendency. ...
Surface-enhanced Raman spectroscopy (SERS) is a highly sensitive and molecule-specific detection technique that uses surface plasmon resonances to enhance Raman scattering from analytes. In SERS system design, the substrates must have minimal or no background at the incident laser wavelength and large Raman signal enhancement via plasmonic confinement and grating modes over large areas (i.e., squared millimeters). These requirements impose many competing design constraints that make exhaustive parametric computational optimization of SERS substrates prohibitively time consuming. Here, we demonstrate a genetic-algorithm (GA)-based optimization method for SERS substrates to achieve strong electric field localization over wide areas for reconfigurable and programmable photonic SERS sensors. We analyzed the GA parameters and tuned them for SERS substrate optimization in detail. We experimentally validated the model results by fabricating the predicted nanostructures using electron beam lithography. The experimental Raman spectrum signal enhancements of the optimized SERS substrates validated the model predictions and enabled the generation of a detailed Raman profile of methylene blue fluorescence dye. The GA and its optimization shown here could pave the way for photonic chips and components with arbitrary design constraints, wavelength bands, and performance targets.
... Among the current detection techniques, it is worth citing optical and mass spectroscopy [6] techniques such as atomic fluorescence spectrometry [7,8], liquid chromatography [9,10], UV-VIS spectrophotometry [11], vibrational spectrometry [12], inductively coupled plasma mass spectrometry [13], graphite furnace atomic absorption spectrometry [14] and flame atomic absorption spectrometry [15]. However, these methods generally require a long detection cycle, and some of them need the use of specific chemicals which may cause secondary pollution. ...
Fast monitoring of water quality is a fundamental part of environmental management and protection, in particular, the possibility of qualitatively and quantitatively determining its contamination at levels that are dangerous for human health, fauna and flora. Among the techniques currently available, Raman spectroscopy and its variant, Surface-Enhanced Raman Spectroscopy (SERS), have several advantages, including no need for sample preparation, quick and easy operation and the ability to operate on the field. This article describes the application of the Raman and SERS technique to liquid samples contaminated with different classes of substances, including nitrates, phosphates, pesticides and their metabolites. The technique was also used for the detection of the air pollutant polycyclic aromatic hydrocarbons and, in particular, benzo(a)pyrene, considered as a reference for the carcinogenicity of the whole class of these compounds. To pre-concentrate the analytes, we applied a methodology based on the well-known coffee-ring effect, which ensures preconcentration of the analytes without any pretreatment of the sample, providing a versatile approach for fast and in-situ detection of water pollutants. The obtained results allowed us to reveal these analytes at low concentrations, close to or lower than their regulatory limits.
... The structure of the datasets is the spectrum, in a certain wavenumber interval, measured for different times after the excitation of the sample. Furthermore, it is applicable also to time-resolved spectra; these investigate the evolution of photo-induced phenomena, as they measure the change of the optical signal (emission, absorption, Raman scattering) as a function of time (e.g., [7][8][9]). ...
This work addresses the problem of determining the number of components from sequential spectroscopic data analyzed by non-negative matrix factorization without separability assumption (SepFree NMF). These data are stored in a matrix M of dimension “measured times” versus “measured wavenumbers” and can be decomposed to obtain the spectral fingerprints of the states and their evolution over time. SepFree NMF assumes a memoryless (Markovian) process to underline the dynamics and decomposes M so that M = WH, with W representing the components’ fingerprints and H their kinetics. However, the rank of this decomposition (i.e., the number of physical states in the process) has to be guessed from pre-existing knowledge on the observed process. We propose a measure for determining the number of components with the computation of the minimal memory effect resulting from the decomposition; by quantifying how much the obtained factorization is deviating from the Markovian property, we are able to score factorizations of a different number of components. In this way, we estimate the number of different entities which contribute to the observed system, and we can extract kinetic information without knowing the characteristic spectra of the single components. This manuscript provides the mathematical background as well as an analysis of computer-generated and experimental sequentially measured Raman spectra.
... Archaeometry [16,17], nanotechnology [18,19], ceramic materials [20], and polymers [21], extraterrestrial materials [22,23], forensic applications [24,25]. Currently, more than consolidated in the scientifi c environment, Raman spectroscopy is well-founded and for a deeper study, some authors can be consulted [26][27][28][29][30]. ...
An analytical development is proposed to determine the solution of the motion equations of a charged particle under the infl uence of an electric fi eld. In the proposal, the advantages and properties of Laplace's transformation are used to map a system of N second-order non-homogeneous diff erential equations into a system composed of N linear equations. From the most general solution for the dynamics of the system, some particular cases were studied to recover, in a simple way, the results present in the literature. To motivate the study, Ehrenfest's theorem is used and we discuss how the classical results can be interpreted in their quantum version. Se propone un desarrollo analítico para determinar la solución de las ecuaciones de movimiento de una partícula cargada bajo la infl uencia de un campo eléctrico. En la propuesta se utilizan las ventajas y propiedades de la transformación de Laplace, para mapear un sistema de N ecuaciones diferenciales no homogéneas de segundo orden en un sistema compuesto por N ecuaciones lineales. A partir de la solución más general para la dinámica del sistema, se estudian algunos casos particulares para recuperar, de manera sencilla, los resultados presentes en la literatura. Para motivar el estudio, se utiliza el teorema de Ehrenfest y se discute como los resultados clásicos pueden ser interpretados en su versión cuántica.
... XRD has been employed throughout industry and research laboratories for more than a century [1], and is well suited to characterize crystalline materials as it captures detailed information regarding the long-range, periodic nature of their structures. NMR and Raman measurements, on the other hand, depend more strongly on localized chemical interactions and are widely used to characterize the structure of molecular materials [2,3]. While their mechanisms and applications may differ, each of these characterization techniques produce similar one-dimensional spectra (sometimes referred to as patterns) containing peaks with distinct positions, widths, and intensities. ...
To assist in the development of machine learning methods for automated classification of spectroscopic data, we have generated a universal synthetic dataset that can be used for model validation. This dataset contains artificial spectra designed to represent experimental measurements from techniques including X-ray diffraction, nuclear magnetic resonance, and Raman spectroscopy. The dataset generation process features customizable parameters, such as scan length and peak count, which can be adjusted to fit the problem at hand. As an initial benchmark, we simulated a dataset containing 35,000 spectra based on 500 unique classes. To automate the classification of this data, eight different machine learning architectures were evaluated. From the results, we shed light on which factors are most critical to achieve optimal performance for the classification task. The scripts used to generate synthetic spectra, as well as our benchmark dataset and evaluation routines, are made publicly available to aid in the development of improved machine learning models for spectroscopic analysis.
... Most basic studies had been limited to a small number of small polarizable molecules such as pyridine, benzoic acid, and its derivatives, or some ionic samples. In 1984, SERS' applicability was first reported as an analytical method for various types of chemicals and biological analytes [15][16][17][18][19]. This technology has shown many advantages in high-sensitivity spectroscopy and disposal of fluorescence radiation. ...
Raman spectroscopy is an important method for the identification of molecules that is widely used to determine the chemical and structural properties of various materials. Many materials have special Raman spectra so that this phenomenon can it has become an effective tool for studying the structural and chemical properties of molecules. Since Raman spectroscopy can provide accurate information on the chemical and structural properties of biological compounds, this method is used in the field of science. Vital and especially in biological and medical studies is rapidly expanding. Raman is inherently weak and sometimes masked by noise and fluorescence. As a result, the study of low-concentration molecules is not feasible and the need to amplify the Raman scattering signal is clearly felt. . One of the efficient methods for studying low and even single molecular concentrations is the Surface Enhanced Raman Scattering (SERS) method. It uses gold, silver, copper and noble metal nanoparticles to enhance the Raman scattering signal. . SERS has been rapidly expanding over the past four decades, as applications for recognition in the fields of chemistry, materials sciences, biochemistry and biosciences are rapidly expanding. Advances in the manufacture of SERS-based biosensors are a major breakthrough in the detection of biological materials in which the electromagnetic field (effect) molecule is affected by the external field, this larger substitute field due to electromagnetic resonance near the metal surface is formed. Mechanisms of electromagnetic field (field effect) amplifiers mainly contribute to the development of SERS, which includes the study of detection performance, direct and indirect fabrication methods for the identification of biological and chemical analytes, Applications of biosensors, amplifiers, and SERS-based biosensor structures to detect biomolecules are briefly described.
... Both techniques have some limitations and challenges that hinder the decision to rely on these systems. Description of the process of Raman scattering can be found in some references such as (Laserna 1996;Smith and Dent 2005). Systems based on laser Raman spectroscopy for detecting explosives and some techniques to increase the range of detection and improve the signal to noise ratio (SNR) are described (Gulati et al. 2019;Mogilevsky et al. 2012;Misra et al. 2010;Gaft and Nagli 2008;Kögler and Heilala 2020). ...
The detection and identifcation of explosive materials is required to defend the military
forces and civilians. In this study we propose an integrated optoelectronics system com-
posed of Raman Spectroscopy System and visible/near infrared hyperspectral camera for
standof real time in situ detection and identifcation of explosive traces on diferent back-
ground materials. Both systems are combined to overcome the limitations when using each
system separately. For the preliminary investigation of the system efciency, the detection
of the most common explosive material, the trinitrotoluene (TNT), is tested. The proposed
HSI system is tested for explosive detection at distance range from 1 to 30 m. The HSI
successfully achieved detection of the traces of TNT at 30 m distance and detection limit
of 1 µg/cm2
. On the other hand, the Raman system could successfully detect a sample of
20 µg/cm2
of TNT at 1 m. Limitations of both systems are discussed. The obtained results
show the ability of the recommended integrated system to overcome the limitations of each
system separately and hence to accurately detect and identify the explosive materials.
... One of the most powerful analytical techniques in the heritage scientist's portfolio is Raman spectroscopy (RS). The technique has been used in HS for more than 40 years, and nowadays it can be considered a routine test to investigate the material composition of artworks, also at the micrometric scale [1]. An increasing number of portable Raman spectrometers was developed [2][3][4][5] and some are now commercial, even if they are mostly optimized for pharmaceutical applications (quick identification of raw materials). ...
Raman spectroscopy (RS) is a powerful non-invasive tool for the characterization of materials. However, the fluorescence effect often hampers the detectability of the relatively weak vibrational Raman signal. Several approaches were exploited to overcome this limit. This work, in particular, evaluates the performance of an in situ portable sequentially shifted excitation (SSE™) Raman spectrometer applied to the examination of artistic historical pigment powders enclosed in glass vials. The explored handheld spectrometer employs a dual, temperature-shifted, 785 nm and 852 nm laser excitation to optimize both spectral coverage and fluorescence subtraction. The study demonstrates the feasibility of the SSE RS approach for non-invasive identification of art materials, and its applicability in complex situations where the examined material cannot be removed from its container. Laboratory measurements using benchtop dispersive micro-Raman spectroscopy at 785 nm are reported for comparison.
... The main advantage is the possibility to investigate precisely functional groups in molecules of both organic and inorganic materials. The analyses are performed in a non-invasive way which allows distinguishing between pigments of the same colour and same composition by exploiting the different structural properties of the compounds (Smith 2005). Pigments and inks may have similar elemental compositions but have different chemical structures, therefore resulting in different molecular vibrations. ...
This work will give an overview of the scientific approach used for the study of written heritage on parchment. Elemental analysis using X-ray fluorescence (XRF) together with compound-specific analytical methods such as Fourier transform infrared (FTIR) and Raman spectroscopy can be applied in a non-invasive way, without the need for sampling and without inducing changes to the object. Physico-chemical investigations are complemented and further deepened by DNA- and biological analyses for the identification of the biological origin of materials and the identification of microorganisms, insects and viruses that might be present on the object which may add valuable information about its history and conservation state.
... In scattering, photons distort and polarise a molecule's electron cloud. As a result of this, a short-lived and unstable 'virtual' state is formed, and a photon is promptly re-radiated afterwards 298 . The light scattering process can be elastic or inelastic. ...
Combustion noise is relevant to current aviation, rocket, and ground-based gas turbine engines, as it contributes to environmental noise pollution and can trigger thermoacoustic instabilities. These consequences are particularly prevalent in lean, premixed, prevaporised combustors, which are designed to reduce nitrous oxide (NOx) emissions. As a result, there is a need to better understand the mechanisms that drive sound generation in such systems. There are two components to combustion noise: direct noise – generated by the unsteady heat release of a flame – and indirect noise – produced by the acceleration of entropic, vortical, or compositional inhomogeneities. Separation of the respective contributions has proven to be complex to achieve in real engines – for this purpose, model experiments have been developed. These are non-reacting experiments that use unsteady, synthetic perturbations to emulate the fundamental physics of combustion acoustics processes and provide clear data for comparison with theory. Indirect noise models have been theorised for compositional perturbations and experimental validation has been provided via the measurement of acoustic waves (i.e. the output), while assuming a constant compositional perturbation (i.e. the input). This thesis follows on from such experiments by simultaneously measuring both acoustic and compositional waves in a model setup, making use of numerical, analytical, and experimental studies. It first builds upon a previous model experiment through a numerical investigation on the generation, mixing, and convection of entropic and compositional waves generated by heat addition and gas injection. The computed temperature and mass fraction fields are compared with experimental results and inform the design of a new model setup – the Canonical Wave Rig (CWR). The CWR is then used to study direct and indirect noise under simplified, well-controlled conditions. Subsonic and sonic (choked) conditions are investigated for a convergent-divergent nozzle. Acoustic, entropic, and compositional perturbations are generated via the co-flow injection of air or methane into a low Mach number mean flow of air. Spontaneous Raman spectroscopy (1.5 kHz) is employed for the time-resolved measurement of the local concentration upstream of the nozzle. Single pulse experiments in the infra-sound range are used to validate the derived analytical model for direct noise due to co-flow injection. The measurement of non-reverberated indirect noise is made for the first time and is contrasted with results obtained via dereverberation (i.e. removing the effect of pressure build up due to acoustic reflections). Indirect noise transfer functions are calculated using the acoustic and compositional measurements, and issues pertaining to the methods applied are highlighted. Lastly, the pulse burst injection of methane at frequencies up to 250 Hz is presented. The goal of these experiments is to provide data at more realistic frequencies and amplitudes.
... Raman spectroscopy provides a non-invasive experimental approach for the assessment of structural and biophysical properties in complex systems [20]. The Raman technique depends on the change in polarizability of a molecule (due to the inelastic scattering of light by molecules) and measures the relative frequencies at which scattering of radiation occurs, while IR spectroscopy depends on a change in the dipole moment [21,22]. ...
The early detection of cancer is a challenging problem in medicine. The blood sera of cancer patients are enriched with heterogeneous secretory lipid-bound extracellular vesicles (EVs), which present a complex repertoire of information and biomarkers, representing their cell of origin, that are being currently studied in the field of liquid biopsy and cancer screening. Vibrational spectroscopies provide non- invasive approaches for the assessment of structural and biophysical properties in complex biological samples.
Methods
In this pilot study, multiple Raman spectroscopy measurements were performed on the EVs extracted from the blood sera of n = 9 patients consisting of four different cancer subtypes (colorectal cancer, hepatocellular carcinoma, breast cancer and pancreatic cancer) and five healthy patients (controls). FTIR (Fourier Transform Infrared) spectroscopy measurements were performed as a complementary approach to Raman analysis, on two of the four cancer subtypes. The spectra were subjected to various machine learning classifiers with hyperparameter optimization to discriminate between healthy and cancer patients-derived EVs. The AdaBoost Random Forest Classifier, Decision Trees, and Support Vector Machines (SVM) distinguished the baseline corrected Raman spectra of cancer EVs from those of healthy controls (N = 18 spectra) with a classification accuracy of >90% when reduced to a spectral frequency range of 1800 − 1940 𝑐𝑚⁻¹ and subjected to a 50:50 training: testing split. FTIR classification accuracy on N = 14 spectra showed an 80% classification accuracy. Our findings demonstrate that basic machine learning algorithms are powerful applied intelligence tools to distinguish the complex vibrational spectra of cancer patient EVs from those of healthy patients. These experimental methods hold promise as valid and efficient liquid biopsy for artificial intelligence-assisted early cancer screening.
... This is a plot of the intensity of the scattered light against the Raman shift in wavenumbers. 23 Intensity of a Raman peak at a particular Raman shift increases as the concentration of molecules responsible for the peak increases. Therefore, a Raman spectrum can be thought of as a molecular fingerprint giving information about the molecules present in the sample through the analysis of the position, height, and width of peaks present in the spectrum. ...
Significance:
The primary method of COVID-19 detection is reverse transcription polymerase chain reaction (RT-PCR) testing. PCR test sensitivity may decrease as more variants of concern arise and reagents may become less specific to the virus.
Aim:
We aimed to develop a reagent-free way to detect COVID-19 in a real-world setting with minimal constraints on sample acquisition. The machine learning (ML) models involved could be frequently updated to include spectral information about variants without needing to develop new reagents.
Approach:
We present a workflow for collecting, preparing, and imaging dried saliva supernatant droplets using a non-invasive, label-free technique-Raman spectroscopy-to detect changes in the molecular profile of saliva associated with COVID-19 infection.
Results:
We used an innovative multiple instance learning-based ML approach and droplet segmentation to analyze droplets. Amongst all confounding factors, we discriminated between COVID-positive and COVID-negative individuals yielding receiver operating coefficient curves with an area under curve (AUC) of 0.8 in both males (79% sensitivity and 75% specificity) and females (84% sensitivity and 64% specificity). Taking the sex of the saliva donor into account increased the AUC by 5%.
Conclusion:
These findings may pave the way for new rapid Raman spectroscopic screening tools for COVID-19 and other infectious diseases.
... Here, we wanted to develop a method that was both rapid as well as did not require use of nanoscale materials for enhancing signals. We utilised the principle that the cross-section of Raman-active modes varies with wavelength, and improves significantly, as the excitation nears pre-resonance or resonance with an electronic state of the sample 32 . The use of resonant Raman spectroscopy has been applied to the study of cytochrome cd1 from bacteria 231 , and UV resonance has been applied to whole bacteria and endospore biomarkers 232 . ...
Development of methods derived from Raman spectroscopy for the detection and identification of bacterial pathogens for clinical and homeland security applications. Results include the elucidation of drug-resistance profiles and differentiation of endospores and vegetative cells, as well as direct detection from bioaerosols and a complex artificial sputum matrix.
... After falling back to the ground state, the electrons release energy as radiation and create more photons than Raman scattering. The consequence is that if the absorption of a sample coincides with the laser wavelength, fluorescence can mask the Raman spectrum (Colthup et al., 1990;Smith and Dent, 2005;Nebu and Sony, 2017). In this case, changing the laser wavelength, adding freshwater, or extracting some compounds from the sample can be helpful. ...
The cuticle covers almost all plant organs as the outermost layer and serves as a transpiration barrier, sunscreen, and first line of defense against pathogens. Waxes, fatty acids, and aromatic components build chemically and structurally diverse layers with different functionality. So far, electron microscopy has elucidated structure, while isolation, extraction, and analysis procedures have revealed chemistry. With this method paper, we close the missing link by demonstrating how Raman microscopy gives detailed information about chemistry and structure of the native cuticle on the microscale. We introduce an optimized experimental workflow, covering the whole process of sample preparation, Raman imaging experiment, data analysis, and interpretation and show the versatility of the approach on cuticles of a spruce needle, a tomato peel, and an Arabidopsis stem. We include laser polarization experiments to deduce the orientation of molecules and multivariate data analysis to separate cuticle layers and verify their molecular composition. Based on the three investigated cuticles, we discuss the chemical and structural diversity and validate our findings by comparing models based on our spectroscopic data with the current view of the cuticle. We amend the model by adding the distribution of cinnamic acids and flavonoids within the cuticle layers and their transition to the epidermal layer. Raman imaging proves as a non-destructive and fast approach to assess the chemical and structural variability in space and time. It might become a valuable tool to tackle knowledge gaps in plant cuticle research.
... It is the preferred method for identifying small MPs <20 μm. 56 For the detection of MPs and NPs, when the technique is used in conjunction with a microscope, the method is referred to as micro(μ)-Raman. 37 Similar to FTIR, Raman spectroscopy provides structural information revealing polymer identity and different kinds of additives in a nondestructive fashion. ...
Microplastics (MPs) and nanoplastics (NPs) constitute a newly recognized class of contaminants of emerging concern in air, soil, water, and food, causing unavoidable exposures to humans and animals. Detection, identification, and quantification of MPs and NPs in environmental matrices and biota is challenging due to the analytes' small size, random morphology, polymeric diversity, applied coatings, and vast surface areas which attract chemical and microbial sorbates. This mini-review explores strengths and weaknesses of analytical methods commonly used for MP and NP identification and quantification, including stereomicroscopy, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, flow cytometry, and mass spectrometry techniques including Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF), pyrolysis gas chromatography-mass spectrometry (Pyr-GC-MS), and liquid chromatography-tandem mass spectrometry. Analytical challenges involved in precise MP/NP detection have been identified and recommendations have been provided to ensure data quality addressing common data quality concerns, including the difficulty of obtaining irrefutable proof that detected polymers originated from the sample as opposed to sample contamination during sample acquisition, sample processing, and analysis.
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... For this reason, longer wavelength sources are best recommended for studies relating to honey using Raman spectroscopy (Paradkar and Irudayaraj 2002;De Oliveira et al. 2002;Batsoulis et al. 2005;Pierna et al. 2011;Chekalyuk and Hafez 2013;Ciaccheri et al. 2015;Corvucci et al. 2015;Kerr et al. 2015;Grazia Mignani et al. 2016b;Frausto-Reyes et al. 2017;Anjos et al. 2018;Salvador et al. 2019;Muller Molnar et al. 2020). A challenge associated with these sources is that they produce low-intensity Raman signals due to the inverse fourth power relation between wavelength and scattering intensity (Smith and Dent 2004;Kerr et al. 2015). Consequently, high-powered sources, cooled detectors and sometimes Fourier Transform (FT) detection schemes become necessary for efficient detection of these low-intensity signals (Bowie et al. 2000). ...
Bees depend on the nectar from flora for the production of honey. Different flora produces unique nectar with varying compositions resulting in almost unlimited varieties in honey. In this work, we have used the 532-nm laser-induced Raman spectroscopic technique, for the first time, to study honey varieties from Iran. The Raman spectra of different kinds of commercial honey samples were obtained using a bench-top Raman microscope. The Raman spectral band intensities improved after activated charcoal pretreatment of the honey samples. The bands of the spectra compared well with molecular designation from literature. Using both supervised and unsupervised multivariate techniques, it was possible to classify and develop models capable of predicting the different kinds of honey while also establishing critical wavelengths that characterise them. This work has been able to provide baseline Raman spectroscopic data and procedure to promote the use of 532-nm laser-induced Raman spectroscopic technique with multivariate methods for the cost-effective analysis of floral honey from Iran.
... These vibration bands are similar to the Raman spectrum of the rutile TiO 2 nanoparticles, which denotes that the rutile's chemical structure had not been changed. Table 3. Assignment of polysulfone characteristic Raman peaks with possible functional groups or specific molecular vibrations, collected from the literature [39][40][41][42][43][44]. In the case of 1 wt.% ...
The blending of nanomaterials into a polymeric matrix is a method known for its ability, under certain circumstances, to lead to an improvement in membrane properties. TiO2 nanoparticles have been used in membrane research for the last 20 years and have continuously shown promise in this field of research. Polysulfone (PSf) membranes were obtained through the phase inversion method, with different TiO2 nanoparticle concentrations (0, 0.1, 0.5, and 1 wt.%) and two types of TiO2 crystalline structure (anatase and rutile), via the addition of commercially available nanopowders. Research showed improvement in all studied properties. In particular, the 0.5 wt.% TiO2 rutile membrane recorded an increase in permeability of 139.7% compared to the control membrane. In terms of overall performance, the best nanocomposite membrane demonstrated a performance index increase of 71.1% compared with the control membrane.
... Raman technique is a powerful analytical tool in food quality and safety inspection, such as detection of mycotoxin and common harmful chemical residues in agri-food products (Huang, Cheng, & Lai, 2020;Jiang, Sun, Pu, & Wei, 2018;Wu, Pu, & Sun, 2021;Zhang, Pu, Huang, & Sun, 2021), microbiota evaluation between raw and processed food (He & Sun, 2015). Both Raman and MIR techniques have the potential to study the vibrations of molecular bonds, but these two spectroscopies are complementary in the fact that: i) the phenomenon observed in Raman is the elastic and inelastic scattering of light (see detailed descriptions from Smith & Dent (2005)), while infrared spectroscopy relies on absorption of infrared light in different amounts and at distinct wavenumbers corresponding to different bond vibrations; ii) Raman spectra usually featured a series of much narrow and sharper spectral peaks than IR spectra. ...
This thesis aimed to show how vibrational spectroscopy including near infrared (NIR), mid infrared (MIR), Raman and NIR hyperspectral imaging (NIR-HSI) coupled with advanced chemometrics can highlight the variability and heterogeneity of both, raw apples and processed purees. Experimental trials were designed to modulate several factors in orchard (varieties, agricultural practices), during post-harvest storage (4°C) and processing (temperature, grinding and refining) in order to modify properties and composition of apples and purees. An efficient approach using NIR-HSI allowed illustrating the distribution of total sugars and dry matter inside apples. The inter-batch variability of apples and the intra-batch variability between individual apples intensively changed the cooked purees. MIR spectroscopy was the best tool to detect the variability of purees and assess their biochemical (soluble solids, acidity, dry matter, fructose, sucrose and malic acid), rheological (viscosity and viscoelastic moduli) and textural (particle size and volume) properties. Good linear correlations were found between apple texture and puree viscosity, as well as between apple and puree acidity, soluble solids and dry matter. Therefore, VIS-NIR and NIR techniques allowed to predict the taste and texture of purees from the non-destructive spectra of apples. Besides, MIR spectroscopy can guide puree formulation from spectra of single-variety purees. Our innovative approaches could provide objective data to better manage apples and to adapt processing conditions according to their initial properties. The ultimate goal is to improve the quality of fresh and processed fruits while reducing losses.
... Таким образом можно рассматривать свет в виде фотонов, которые рассеиваются при взаимодействии с молекулами материи. Количество молекул рассеянных вследствие взаимодействия пропорциональны размеру связей в молекулах [208,209]. В основе спектроскопии КР (далее СКР) лежит детектирование неэластичного рассеянного света при обмене колебательной и вращательной энергий между зондирующим излучением и молекулами облучаемой ткани. На рисунке 3 представлена диаграмма Яблонского на которой можно увидеть возбуждение молекулы фотоном и последующий ее переход в виртуальное состояние. ...
В данной диссертационной работе при помощи методов многофотонной томографии (МФТ) и спектроскопии комбинационного рассеяния (СКР) было изучено влияние, оказываемое местным применением оптических просветляющих агентов (ОПА) с различной осмолярностью на свиную кожу ex vivo. Было проведено сравнение воздействия растворов глицерина и йогексола (Омнипак-300) на сигналы автофлуоресценции (АФ) и генерации второй гармоники (ГВГ) на различных глубинах в коже. Омнипак-300 был впервые использован для МФТ измерений. Было показано, что применение обоих ОПА позволяет значительно увеличить глубину зондирования при МФТ измерениях, а также улучшить контраст и качество получаемых изображений. Было показано, что 60-ти минутное местное применение Омнипак-300 вызывает увеличение сигнала автофлуоресценции до 1.50±0.05 раза, сигнала генерации второй гармоники до 3.00±0.03 раз. В тоже время, Омнипак-300 не оказывал какого-либо видимого воздействия на морфологию ткани в отличие от глицерина. Также были показаны результаты изучения изменений спектров КР свиной кожи, вызванных применением ОПА. Эффективность воздействия глицерина и Омнипак-300 были сравнены с контрольными образцами кожи (без воздействия ОПА). Результаты исследований показали, что интенсивность КР линий, типичных для кожи существенно увеличивалась на глубинах, превышающих 40 мкм, после применения глицерина, и на глубинах превышающих 160 мкм, после применения Омнипак-300. В частности, было показано, что 60-ти минутное местное применение Омнипак-300 вызывает увеличение интенсивности характерных молекулярных линий спектра КР на 937 см–1, 1003 см–1, 1244 см–1, 1272 см–1,
1426 см–1 и 1665 см–1 до 1.40±0.03, 1.43±0.04, 1.45±0.04, 1.52±0.05, 1.44±0.03 и 1.51±0.04 раз, соответственно. Было изучено влияние ОПА с различной смолярностью на гидратацию коллагена. Результаты показали, что Омнипак-300 вызывает меньшую дегидратацию коллагена (не более 1.18±0.09 раза) по сравнению с действием глицерина (не более 1.66±0.07 раза). Изучение воздействия Омнипак-300 на гидратацию коллагена методом спектроскопии КР было осуществлено впервые. Было изучено влияние двух типов ОПА различной осмолярности (глицерин и Омнипак-300) на полное содержание воды в коже, а также на содержание различных компонентов воды в зависимости от силы ее водородной связи (жестко связанная, сильно связанная, слабо связанная и несвязанная вода), при местном применении агентов.
Результаты показали, что Омнипак-300 вызывает меньшую дегидратацию всей кожной ткани (не более 1.21±0.06 раза) по сравнению с действием глицерина (не более 2.26±0.05 раза). Было выдвинуто предположение, что поскольку слабо связанная и сильно связанная вода составляет около 93% от полного состава воды в коже, данные типы воды в наибольшей степени вовлечены во взаимодействие с ОПА. Таким образом, эффективность ОП напрямую связана с одним из ключевых механизмов ОП (дегидратацией) и зависит от степени
уменьшения содержания воды при действии ОПА, что надежно регистрируется с помощью конфокальной КР спектроскопии. Впервые было показано воздействие ОПА с разной осмолярностью на различные типы воды в зависимости от силы ее водородной связи.
... This is a plot of the intensity of the scattered light against the Raman shift in wavenumbers. 18 Intensity of a Raman peak at a particular Raman shift increases as the concentration of molecules responsible for the peak increases. A Raman spectrum can therefore be thought of as a molecular fingerprint giving information about the molecules present in the sample through the analysis of the position, height, and width of peaks present in the spectrum. ...
Significance: The primary method of COVID-19 detection is reverse transcription polymerase chain reaction (RT-PCR) testing. PCR test sensitivity may decrease as more variants of concern arise.
Aim: We aimed to develop a reagent-free way to detect COVID-19 in a real-world setting with minimal constraints on sample acquisition.
Approach: We present a workflow for collecting, preparing and imaging dried saliva supernatant droplets using a non-invasive, label-free technique known as Raman spectroscopy to detect changes in the molecular profile of saliva associated with COVID-19 infection.
Results: Using machine learning and droplet segmentation, amongst all confounding factors, we discriminated between COVID-positive and negative individuals yielding receiver operating coefficient (ROC) curves with an area under curve (AUC) of 0.8 in both males (79% sensitivity, 75% specificity) and females (84% sensitivity, 64% specificity). Taking the sex of the saliva donor into account increased the AUC by 5%.
Conclusion:These findings may pave the way for new rapid Raman spectroscopic screening tools for COVID-19 and other infectious diseases.
... Upon the interaction with the sample, the frequency of photons in monochromatic light changes as they are absorbed by the sample and then reemitted. The shifting frequency of the reemitted photons from the sample is then compared with the original monochromatic frequency to form a Raman effect [23,130]. Surface-enhanced Raman spectroscopy (SERS) is the enhanced version of Raman spectroscopy with a better amplification of electromagnetic fields created by the excitation of localised surface plasmon. SERS can detect samples in a low concentration of analytes with high sensitivity [23]. ...
Large-scale food-borne outbreaks caused by Salmonella are rarely seen nowadays, thanks to the advanced nature of the medical system. However, small, localised outbreaks in certain regions still exist and could possess a huge threat to the public health if eradication measure is not initiated. This review discusses the progress of Salmonella detection approaches covering their basic principles, characteristics, applications, and performances. Conventional Salmonella detection is usually performed using a culture-based method, which is time-consuming, labour intensive, and unsuitable for on-site testing and high-throughput analysis. To date, there are many detection methods with a unique detection system available for Salmonella detection utilising immunological-based techniques, molecular-based techniques, mass spectrometry, spectroscopy, optical phenotyping, and biosensor methods. The electrochemical biosensor has growing interest in Salmonella detection mainly due to its excellent sensitivity, rapidity, and portability. The use of a highly specific bioreceptor, such as aptamers, and the application of nanomaterials are contributing factors to these excellent characteristics. Furthermore, insight on the types of biorecognition elements, the principles of electrochemical transduction elements, and the miniaturisation potential of electrochemical biosensors are discussed.
Digital technologies hold enormous potential for improving the performance of future-generation sorting and processing plants; however, this potential remains largely untapped. Improved sensor-based material flow characterization (SBMC) methods could enable new sensor applications such as adaptive plant control, improved sensor-based sorting (SBS), and more far-reaching data utilizations along the value chain. This review aims to expedite research on SBMC by (i) providing a comprehensive overview of existing SBMC publications, (ii) summarizing existing SBMC methods, and (iii) identifying future research potentials in SBMC. By conducting a systematic literature search covering the period 2000-2021, we identified 198 peer-reviewed journal articles on SBMC applications based on optical sensors and machine learning algorithms for dry-mechanical recycling of non-hazardous waste. The review shows that SBMC has received increasing attention in recent years, with more than half of the reviewed publications published between 2019 and 2021. While applications were initially focused solely on SBS, the last decade has seen a trend toward new applications, including sensor-based material flow monitoring, quality control, and process monitoring/control. However, SBMC at the material flow and process level remains largely unexplored, and significant potential exists in upscaling investigations from laboratory to plant scale. Future research will benefit from a broader application of deep learning methods, increased use of low-cost sensors and new sensor technologies, and the use of data streams from existing SBS equipment. These advancements could significantly improve the performance of future-generation sorting and processing plants, keep more materials in closed loops, and help paving the way towards circular economy.
Using Raman spectroscopy, the study of a polymorphic phase transition in the KNNLiTaLa0.01 compound is presented. An analysis of the behavior with temperature, wavenumber and half width at full maximum of the individual bands, corresponding to the vibration modes of the (Nb/Ta)O6 octahedra of the KNNLiTaLa0.01 compound’s structure, is performed. This analysis determined that the polymorphic phase transition of the KNNLiTaLa0.01 compound occurs in the 90 to 105°C temperature interval. Using the Hard Mode Spectroscopy method, the value of the critical exponent of the order parameter was determined to be β ≈ ½, indicative of a second order transition.
This paper proposes a method to identify the blood of 4 poultry species (chicken, duck, goose and pigeon) based on Raman spectroscopy and its baseline. Samples were prepared by pretreatment methods of freezing, thawing, and dilution. The Raman spectra of dynamic blood and static blood were measured, respectively, and the spectral differences between the two research schemes were analyzed. The four species of poultry blood were identified based on the Raman spectroscopy and its baseline. The results show that the method can realize the identification of four species of poultry blood. In addition, the potential of Raman spectroscopy as a technique for determining carotenoids in blood has been clearly confirmed, which opens up the possibility to quickly determine whether poultry eats feed containing carotenoids without sample preparation.
As recent years have shown an increasing use of polymers for the fabrication of firearms, it is necessary to develop techniques for the reconstruction of obliterated serial numbers that are stamped in these materials. Hyperspectral Raman imaging has proven to be a suitable technique for this purpose, as it is sensitive to residual strain. The extraction of relevant information however requires an advanced two‐step fitting procedure (i.e. the identification of strain‐sensitive peaks followed by the fitting itself) that may be somewhat time consuming. In this study, Principal Component Analysis (PCA), an exploratory method of the Raman data is proposed to overcome this deficit. The results show that PCA offers better visual contrast in comparison to the previously reported mathematical modelling technique, as it is able to highlight pertinent variance in the original dataset, for multiple polymers, such as polycarbonate, polyethylene, nylon and nylatron. Results obtained by limiting acquisition times and spectral ranges have displayed no significant loss of information and therefore reconstruction abilities in polyethylene. A normal density function model and Receiver Operating Characteristic (ROC) curves have been used to show that score matrices obtained from PCA are suitable for separation of distinct strained and unstrained pixel populations. Additionally, binary images favoring minimization of the false positive rate are created to enhance observable contrast allowing for easier character recognition. Finally, a recommended routine analysis is offered to forensic scientists wanting to apply these methods in order to aid criminal investigations or trials.
Electronic biosensors based on novel 2D materials such as graphene or graphene oxide
could be such a platform for the early detection of diseases. The focus of this
dissertation was on the synthesis of highly sensitive 2-D graphene oxide (GO) and its
implementation as a sensitive measuring layer (transducer) for the formation of
graphene oxide-based ion-sensitive field effect transistors (ISFETs), with the aim of
developing an innovative biosensor concept.
Using surface micromechanics methods, GO was microstructured and contacted with
interdigital electrodes via lithography steps. Only when the thin films were converted
into partially “reduced” graphene oxide (rGO) by thermal annealing, the intrinsic
charge carrier properties could be made usable. The novel process for thermal
annealing in electrically conductive graphene oxide within one second was carried out
with the RTP-oven (Rapid Thermal Processing). The changes in the material properties
of the GO thin film were spectroscopically and electronically characterized, with the
unambiguous finding of a temperature optimum for thermal layer healing. After the
extensive development of the process line to produce rGO-based ISFETs, various
concentrations of the hormone NT-proBNP were detected in 150 mM human serum
by using these sensors. Following the definition of the New York Heart Association,
the concentration-dependent measurement signals could be clearly assigned to the
clinically relevant area via the dose-effect curve.
The feasibility of synthesizing graphene quantum dots from spent resin in a nuclear power plant that was subject to decommissioning was experimentally analyzed, and the resulting reduction in disposal cost was estimated. Owing to radiation safety and regulatory issues, graphene quantum dots were synthesized using an uncontaminated ion‐exchange resin, IRN150 H/OH, prior to its use in a nuclear power plant. The synthesis of graphene quantum dots was attempted, and the characteristics were analyzed using atomic force microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The characterization of synthesized graphene quantum dots showed it was possible to recycle the spent resin into graphene quantum dots. Considering the amount of spent resin at the Wolsong Nuclear Power Plant, it is estimated that 3932 drums of ILW reduce to 1636 drums of LLW and 786 drums of EW, and the disposal cost reduces by 42 310 612 USD, indicating the reduction of 79%. The feasibility of synthesizing graphene quantum dots from spent resin in a nuclear power plant that was subject to decommissioning was experimentally analyzed. The synthesis of graphene quantum dots was attempted, and the characteristics were analyzed using atomic force microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The characterization of synthesized graphene quantum dots showed it was possible to recycle the spent resin into graphene quantum dots.
Raman scattered light is generated by the interaction of irradiated light with molecular vibrations, and it provides molecular information. Although Raman shifts of peaks in the low-frequency region (< 200 cm-1) provide useful information related to molecular structures, there are no reliable materials available for calibrating Raman spectrometers in this region. In this study, we chose high-purity L-cystine (NMIJ CRM 6025-a) and used it to reliably evaluate Raman shifts of peaks with uncertainty by a combination of HeNe laser and Ne emission lines. To evaluate their uncertainty, we considered the uncertainty originating from wavenumbers of Ne emission lines and HeNe laser, evaluation of wavenumber for peak-tops and changes in temperature. The obtained Raman shifts of eight peaks from 9 to 160 cm-1 and their uncertainty were 0.3 cm-1 or 0.4 cm-1 and these values were validated with the results using a 532 nm laser.
The increasing demand for single-use plastic-based products worldwide has generated immense waste during the last decade. This review aims to summarize the current developments of surface-enhanced Raman spectroscopy (SERS) for detecting micro- and nanoplastics in a variety of samples and environments. Despite the SERS technique being very recent for this purpose, its robustness has already been discussed in a few analyses focused on well-known pollutants such as phthalates, plasticizers, and xenobiotic contaminants from commercially available water bottles. Here, the latest advances, obstacles, and perspectives are reviewed using SERS detection as a robust alternative for analyzing complex samples containing nanoplastic particles present in daily consumer products such as wine and vegetables. Moreover, this paper describes different SERS substrates developed to overcome the limitations for identifying polymer particles at low concentrations. Factors contributing to the sensitivity of SERS substrates are discussed to show the advantages and limitations of this technique. The broader role of SERS as a tool in environmental research is currently explored from polluted air and aquatic environments, which can be relevant for other fields, such as clinical monitoring and nanotoxicology.©2022 Wiley-VCH GmbH
The necessity for the development of highly sensitive and selective detection techniques for the investigation of biomolecules are inevitable. Surface plasmon resonance (SPR) based biosensor has developed as a sustainable and commercially applicable tool for this investigation. The detection of biomolecules, that are either toxic or useful to the environment, and the early diagnosis of disease biomarkers together come up with the key for better living. The exploration of this should give the prime concern for the real-time detection techniques that are cost-effective and least time-consuming. Here, we have briefly introduced the properties, classifications and characteristics of nanomaterials and that of the biosensors, we carefully analysed the properties of nanomaterials that can enhance sensor’s activity. We have given much importance to the recent development in the field of biosensing and the role of different nanomaterials including gold, silver, magnetic and 2D nanomaterials in enhancing the properties of SPR sensors under various configurations with explaining the principle and mechanism of SPR in brief. Along with this, we have addressed the phase matching schemes for SPR and the coupling of SPR with other modes such as guided modes, phonon polariton and defect modes in enhancing performance. The role of other plasmons such as Tamm plasmons and Bloch surface waves are also included in the review.
In an upper-division interdisciplinary laboratory experiment, students use Raman spectroscopy to highlight how the overall structure and conformational order of lipid bilayers can be influenced by their individual phospholipid composition. Students prepare a supported lipid bilayer, as a model cell membrane, by spreading liposomes made of various phospholipids on a solid support. The characterization of phospholipid bilayers, a major component of cellular membranes, can advance our fundamental understanding of important biological phenomena, with significant implications in various fields including drug delivery and development. We use Raman spectroscopy as an analytical tool to investigate the structural and packing properties of model cell membranes. The spectral frequency, intensity, and line-width of lipid Raman bands are extremely sensitive to structural alterations. This experimental module effectively exposes students to the fundamentals of Raman spectroscopy and teaches students the importance of interdisciplinary education as they integrate concepts from chemical structure, molecular interactions, and analytical spectroscopic techniques to gain a more holistic understanding of biological membrane properties.
Raman spectroscopy provides accurate and cost‐effective quality control of pharmaceuticals, which is essential for maintaining the confidence of dispensing physicians and patient's adherence to therapeutic regimens. For drug salts that contain a counter‐ion, the active pharmaceutical ingredient and counter‐ion combination is optimized for the intended therapeutic effect. Drug salts with multiple alternative counter‐ions are developed, dosed, and regulated independently and case study one demonstrates how an adulterated medication can contain a different counter‐ion than the label claim. Three additional case studies are performed that showcase how Raman spectroscopy can be applied as a cost‐effective alternative detection technique of both label claim drug and counter‐ion when compared to more commonly used HPLC‐UV methods. This study showcases Raman spectroscopy's ability to efficiently identify an adulterated medication sold in the United States. Compared to HPLC‐UV, Raman spectroscopy is an excellent technique for surveillance of drugs and counter ions in medications as demonstrated across four case studies.
Enhancing the light-matter interactions is important for many different applications like sensing, surface enhanced spectroscopies, solar energy harvesting, and for quantum effects such as nonlinear frequency generation or spontaneous and stimulated emission. Hybrid metal-dielectric nanostructures have shown extraordinary performance in this respect, demonstrating their superiority with respect to bare metallic or high refractive index dielectric nanostructures. Such hybrid nanostructures can combine the best of two worlds: strong confinement of the electromagnetic energy by metallic structures and high scattering directivity and low losses of the dielectric ones. In this review, following a general overview of the properties of metal-dielectric nanostructures, some of their most relevant applications including directional scattering, sensing, surface enhanced Raman spectroscopy, absorption enhancement, fluorescence and quantum dot emission enhancement, nonlinear effects, as well as lasing, are summarized.
This book contains chapters describing advanced modes of atomic force microscopy (AFM) and Raman spectroscopy. It also provides an in-depth understanding of advanced AFM modes and Raman spectroscopy for characterizing various materials. This volume is a useful resource for a wide range of readers, including scientists, engineers, graduate students, postdoctoral fellows, and scientific professionals working in specialized fields such as AFM, photovoltaics, 2D materials, carbon nanotubes, nanomaterials, and Raman spectroscopy.
Chapters
1. Application of Atomic Force Microscopy in Organic and Perovskite Photovoltaics, By Chandra Shakher Pathak
2. Nanomaterials Characterisation through Magnetic Field Dependent AFM, By Marco Coïsson, Gabriele Barrera, Federica Celegato and Paola Tiberto
3. Diffraction Grating Groove Metrology Using AFM & STM, By Leonid I. Goray
4. Atomic Force Microscopy Reveals the Role of Vascular Smooth Muscle Cell Elasticity in Hypertension, By Yi Zhu
5. Deep Learning Approach for Raman Spectroscopy, By M.H. Wathsala N. Jinadasa, Amila C. Kahawalage, Maths Halstensen, Nils-Olav Skeie and Klaus-Joachim Jens
6. High-Wavenumber Raman Analysis, By Shan Yang
7. Resonance Raman Spectroscopy Investigation of the Interaction of Molecules Adsorbed on Solid Acid Surfaces, By Lucia Kiyomi Noda
8. Raman Spectroscopy for Characterization of Hydrotalcite-like Materials Used in Catalytic Reactions, By Luciano Honorato Chagas, Sandra Shirley Ximeno Chiaro, Alexandre Amaral Leitão and Renata Diniz
9. Raman Spectroscopy in the Analysis of Textile Structures, By Dorota Puchowicz and Malgorzata Cieslak
10. Application of Raman Spectroscopy in Biomedical Diagnostics, By Nikiwe Mhlanga, Phumlani Tetyana, Sanele Nyembe and Lucky Sikhwivhilu
11. Raman Spectroscopy and Mapping Analysis of Low-Dimensional Nanostructured Materials and Systems, By Karthikeyan Krishnamoorthy and Sang-Jae Kim
12. Tip-Enhanced Raman Spectroscopy of 2D Semiconductors, By Mahfujur Rahaman and Dietrich R.T. Zahn
13. Raman Features of Linear-Carbon-Chain and Multiwall Carbon Nanotube Composites, By Yahachi Saito and Koji Asaka
We investigated the structural properties of organic–inorganic lead halide perovskite microwires through joint experimental and theoretical Raman spectroscopy. High‐quality methyl ammonium lead iodide (MAPBI3, MA = CH3NH3+) microwires with tetragonal phases and explicit crystalline orientation were prepared. Raman spectroscopy was used in studying the as‐prepared microwires and determining not only the crystal quality but also crystalline orientation of MAPBI3 with the aid of normal mode calculations. High‐quality structural features were verified by well‐resolved Raman peaks related to the inorganic cage (IPbI stretching and bending modes below 100 cm−1), organic MA cation motions (libration ~150–200 cm−1 and torsional ~200–250 cm−1), a coupled mode of cage and MA cation liberation (~105–110 cm−1), and the almost undetectable degraded signal at 95 cm−1. In micro‐Raman mapping, an intensity ratio of 105 and 95 cm−1 was used for the direct imaging of crystal quality along the microwire. The characterization of the crystalline orientation of MAPBI3 microwires posed a challenge, which can be addressed by using polarized Raman technique with normal mode analysis. We believe that the proposed method can be extended to other organic–inorganic lead halide perovskites with different structures, such as polycrystalline films and single crystals. High‐quality structural features of methyl ammonium lead iodide (MAPBI3) microwires can be verified by well‐resolved Raman peaks. In micro‐Raman mapping, an intensity ratio of 105 and 95 cm−1 was used for the direct imaging of crystal quality along the microwire. The proposed method can be extended to other organic–inorganic lead halide perovskites with different structures, such as polycrystalline films and single crystals.
The improvement in energy efficiency is recognized as one of the significant parameters for achieving our net-zero emissions target by 2050. One exciting area for development is conventional carbon capture technologies. Current amine absorption-based systems for carbon capture operate at suboptimal conditions resulting in an efficiency loss, causing a high operational expenditure. Knowledge of qualitative and quantitative speciation of CO2-loaded alkanolamine systems and their interactions can improve the equipment design and define optimal operating conditions. This work investigates the potential of Raman spectroscopy as an in situ monitoring tool for determining chemical species concentration in the CO2-loaded aqueous monoethanolamine (MEA) solutions. Experimental information on chemical speciation and vapour-liquid equilibrium was collected at a range of process parameters. Then, partial least squares (PLS) regression and an artificial neural network (ANN) were applied separately to develop two Raman species calibration models where the Kent–Eisenberg model correlated the species concentrations. The data were paired and randomly distributed into calibration and test datasets. A quantitative analysis based on the coefficient of determination (R2) and root mean squared error (RMSE) was performed to select the optimal model parameters for the PLS and ANN approach. The R2 values of above 0.90 are observed for both cases indicating that both regression techniques can satisfactorily predict species concentration. ANN models are slightly more accurate than PLS. However, PLS (being a white box model) allows the analysis of spectral variables using a weight plot.
Casein is one of the proteins that has been used in historical works and traces of its use have always been seen throughout history. Casein is extracted from mammalian milk, especially cow's milk, and is used in works of art such as painting staples, paper slats, wood veneers, additives in gypsum mortars, or as an adhesive in the field of Conservation and restoration. The purpose of this study was to introduce the applications of casein, how to make this material as an adhesive, the structure and study of the physical properties created from the use of casein in works such as paintings and historical mortars, and finally to introduce methods and chemical analysis in To identify this natural substance in historical works. According to the findings of this study, it was determined: A: Casein, hydrated lime, sodium oxides and silicates, metal salts and water are suitable compounds for making casein adhesive B: Casein structure is more spherical and has a hydrophilic and hydrophobic part Which causes waterproofing in some historical works such as paintings. c: Instrumental analyzes such as Raman spectroscopy, gas chromatography-mass spectrometry (GC-MS), thin layer chromatography (TLC) and more chemical methods (Spot test) such as Ninhydrin test and Biore test is used to identify proteins, especially casein.
In recent years, fentanyl and its analogs have been increasingly abused, leading to tragic outcomes. One way to tackle this problem is to rapidly detect fentanyl analog compounds and prevent them from reaching people who could be harmed by them. However, the emergence of novel fentanyl analogs that evade detection by classic mass spectral library matching has exacerbated the problem. We propose supervised machine learning classification models as a complementary approach to library matching for detecting fentanyl analogs from mass spectra. To develop and apply such models, we extract two dozen peak-based and similarity-based input features from each spectrum of interest. Using techniques such as random forests, neural networks, and logistic regression, we identify patterns within these features’ values, resulting in strong detection performance. Within a cross-validation framework, we achieve 99% probability of detection and 1% probability of false alarm on a representative set of several thousand mass spectra. These results suggest that machine learning models may offer a robust complement to library matching. Practitioners from diverse fields, including border security, law enforcement, and military may benefit from this capability to detect drugs of abuse.
The Quality by Design (QbD) approach to the production of therapeutic monoclonal antibodies (mAbs) emphasizes an understanding of the production process ensuring product quality is maintained throughout. Current methods for measuring Critical Quality Attributes (CQAs) such as glycation and glycosylation are time and resource intensive, often, only tested offline once per batch process. Process Analytical Technology (PAT) tools such as Raman Spectroscopy combined with Chemometric modelling can provide real time measurements process variables and are aligned with the QbD approach. This study utilises these tools to build Partial Least Squares (PLS) regression models to provide real time monitoring of glycation and glycosylation profiles. In total, 7 cell line specific chemometric PLS models; % mono‐glycated, % non‐glycated, % G0F‐GlcNac, % G0, % G0F, % G1F and % G2F were considered. PLS models were initially developed using small scale data to verify the capability of Raman to measure these CQAs effectively. Accurate PLS model predictions were observed at small scale (5L). At manufacturing scale (2000L) some glycosylation models showed higher error, indicating that scale may be a key consideration in glycosylation profile PLS model development. Model robustness was then considered by supplementing models with a single batch of manufacturing scale data. This data addition had a significant impact on the predictive capability of each model, with an improvement of 77.5% in the case of the G2F. The finalised models show the capability of Raman as a PAT tool to deliver real time monitoring of glycation and glycosylation profiles at manufacturing scale. This article is protected by copyright. All rights reserved.
Raman spectroscopy is increasingly being used in biology, forensics, diagnostics, pharmaceutics and food science applications. This growth is triggered not only by improvements in the computational and experimental setups but also by the development of chemometric techniques. Chemometric techniques are the analytical processes used to detect and extract information from subtle differences in Raman spectra obtained from related samples. This information could be used to find out, for example, whether a mixture of bacterial cells contains different species, or whether a mammalian cell is healthy or not. Chemometric techniques include spectral processing (ensuring that the spectra used for the subsequent computational processes are as clean as possible) as well as the statistical analysis of the data required for finding the spectral differences that are most useful for differentiation between, for example, different cell types. For Raman spectra, this analysis process is not yet standardized, and there are many confounding pitfalls. This protocol provides guidance on how to perform a Raman spectral analysis: how to avoid these pitfalls, and strategies to circumvent problematic issues. The protocol is divided into four parts: experimental design, data preprocessing, data learning and model transfer. We exemplify our workflow using three example datasets where the spectra from individual cells were collected in single-cell mode, and one dataset where the data were collected from a raster scanning–based Raman spectral imaging experiment of mice tissue. Our aim is to help move Raman-based technologies from proof-of-concept studies toward real-world applications. Raman spectroscopy is increasingly being used in biological assays and studies. This protocol provides guidance for performing chemometric analysis to detect and extract information relating to the chemical differences between biological samples.
Although ultraviolet (UV) laser Raman spectroscopy offers the benefits of stronger signals, partial separation of fluorescence and Raman spectra, and increased eye safety, it suffers from excessive noise, poor resolution, low maturity level, and small intensities of remotely acquired signals and therefore needs to be used in combination with effective denoising techniques. Herein, a denoising approach denoted as iterative differential autoregressive spectrum estimation was developed relying on the assumption that more detailed Raman peaks can be obtained by dividing the Raman spectrum into multiple layers with different intensity levels and estimating the energy distribution of each layer. Specifically, each layer was computed from the difference between the upper layer spectrum and its autoregressive model estimation spectrum, and the energy distribution at progressively lower intensity levels was considered. Compared with traditional techniques, our method exhibited good noise suppression performance and an excellent Raman peak restoration ability while offering the advantages of decreased spectral resolution loss and stable robustness. Cutoff optimization strategies were proposed to improve convergence and noise suppression ability and thus decrease the calculation time to 0.18 s and meet the needs of remote Raman spectrometers for real‐time denoising under the condition of long integration. The developed technique paves the way to Raman spectrum denoising based on power spectrum estimation, has a strong adaptive potential, and can be extended to other applications. Iterative differential autoregressive spectrum estimation is a new denoising approach for real‐time long‐integration Raman spectra by dividing the Raman spectrum into multiple layers with different intensity levels and estimating the energy distribution of each layer.
As the structure and behavior of molecules and crystals depend on their different symmetries, group theory becomes an essential tool in many important areas of chemistry. It is a quite powerful theoretical tool to predict many basic as well as some characteristic properties of molecules. Whereas quantum mechanics provide solutions of some chemical problems on the basis of complicated mathematics, group theory puts forward these solutions in a very simplified and fascinating manner. Group theory has been successfully applied to many chemical problems. Students and teachers of chemical sciences have an invisible fear from this subject due to the difficulty with the mathematical jugglery. An active sixth dimension is required to understand the concept as well as to apply it to solve the problems of chemistry. This book avoids mathematical complications and presents group theory so that it is accessible to students as well as faculty and researchers. Chemical Applications of Symmetry and Group Theory discusses different applications to chemical problems with suitable examples. The book develops the concept of symmetry and group theory, representation of group, its applications to I.R. and Raman spectroscopy, U.V spectroscopy, bonding theories like molecular orbital theory, ligand field theory, hybridization, and more. Figures are included so that reader can visualize the symmetry, symmetry elements, and operations.
Single, micrometer-size particles are routinely analyzed for molecular constituents in a recently developed Raman microprobe. Identification as to the principal molecular species present in such samples is made on the basis of the recorded Raman spectrum. Considerations important to successful analysis of microparticles by Raman spectroscopy and the unique aspects of the design of the new microprobe are described. Present capabilities for the detection and identification of various types of environmentally significant species are demonstrated. Raman spectra are discussed for single particles, down to 1 μ m in size, of common inorganic compounds, minerals and selected organic compounds. Emphasis is placed on the speciation of sulfur (e.g., HSO − 4 , SO 2− 4 , SO 2− 3 ) in microparticles. Preliminary results on liquid sulfate particles generated from sulfuric acid aerosol are presented. Other species of interest, such as NH + 4 , NO − 3 , CO 2minus; 3 , and PO 3− 4 are shown to be readily identifiable as major components of airborne particles. The method is applied to the chemical identification of particles in the primary size fraction (> 2 μ m) of ambient air particulate samples. Specific results of analyses which are discussed highlight the general utility of the technique and the important types of analytical information obtained in its application. The importance of unambiguous sampling and the application of the probe to the study of the sampling process are described.
A confocal remote fibre-optic probe has been designed and tested. The theoretical design rationale for the development of the probe is presented in detail. Tailor-made optics have been introduced at both input and output positions of each fibre optic to ensure laser collimation, maximum efficiency and enhancement of Raman scattering. The probe design takes advantage of the pinhole nature of the optical fibre to apply the principles of confocal microscopy. In addition, interchangeable optics provide variable depth discrimination. The incorporation of a miniaturized video camera on the body of the microprobe allows simultaneous optical imaging during Raman spectra acquisition. The efficiency and versatility of the microprobe for a whole range of materials are demonstrated.
Polarized Fourier transform Raman spectra of samples of tetrahydrofuran and carbon tetrachloride were obtained as a function of sample displacement from the optimum focus of the spectrometer collection optics. It was found that the relative intensities of the Raman bands within a spectrum could vary significantly as a function of sample displacement. This was manifested predominantly as a suppression of strongly polarized bands near 1000 cm−1 Raman shift, although the absence of any variation in the CCl4 spectrum eliminates pure polarization effects as the sole cause of these observations. These results are important, as spectra of acceptable signal-to-noise ratio can be obtained with large sample displacements with this spectrometer, hence necessitating careful checking of the sample alignment when making quantitative measurements. The magnitude of the effects were extremely sample dependent.
The approach adopted for the scientific design of methane partial oxidation catalysts has identified oxides that are capable of activating methane and oxygen, but do not destroy methanol, the desired product.From the perspective of methanol stability Sb2O3 showed the best performance, destroying only 3% of the methanol feed at 500°C. The majority of oxides totally combusted methanol below 400°C. The oxides MoO3, Nb2O5, Ta2O5 and WO3 all produced high methanol conversion, however, high selectivities towards formaldehyde and dimethylether were obtained with only low levels of carbon oxides throughout the range of conversions. The products formaldehyde and dimethylether were desirable by-products from a methane partial oxidation process hence these oxides are suitable catalyst components.The activation of methane has been probed by the exchange reaction with deuterium under non-oxidative conditions. The most active catalyst was Ga2O3 which exhibited normalised exchange rates several orders of magnitude greater than the other catalysts. A relationship between the rate of methane activation and the predicted basic strength of the rare earth sesquioxides was established. This relationship indicates that methane activation took place via the abstraction of H+ to form a surface methyl carbanion species.On the basis of these results we have designed and tested a limited range of two component oxide catalysts for methane partial oxidation. The best catalyst was Ga2O3/MoO3 prepared by physically mixing the component oxides. This catalyst showed an increased methanol yield compared with the homogeneous gas phase reaction in the reactor tube packed with quartz chips. The increased methanol yield has been attributed to the development of a co-operative effect between the Ga2O3 and MoO3 oxide phases. The degree of success from this approach indicates the validity of this novel study.
The infrared technology presented in this paper provides a mechanism for the detailed study of PyBOP [(1H-benzotriazole-1- yloxy)tripyrrolidinophosphonium hexafluorophosphate] ester activation in a solid-phase supported chemical system. Prior to this work, formation of the alkoxyphosphonium salt had been postulated as a necessary reactive intermediate for formation of the triazoleactivated ester in the PyBOP activation process; however, observation of the alkoxyphosphonium salt has not been reported at room temperature. The present work not only confirms the presence of the salt but further demonstrates it to be the primary activated species for couplings performed on the solid phase at room temperature. More important than the specific identification of the PyBOP activation method is the general introduction of a set of infrared analytical tools for analysis of solid-phase reaction mechanisms and kinetics.
The Raman spectra of six polymorphic crystal forms of N-cyano-N'-methyl-N"-{2-[(5-methyl-1H-imidazol-4-yl)methylthio]ethyl}-guanidine (Cimetidine) have been studied to investigate the possibility of quantitative analysis of polymorphic mixtures. Characteristic Raman bands of the various polymorphs have been found, some of which proved to be appropriate for quantitative analysis. The applicability of various mathematical techniques has been investigated, of which partial least-squares (PLS) has been found to be the best.
Silicon integrated circuits are fabricated by the creation of complex layered structures. The complexity of these structures provides many opportunities for impurities, improperly annealed dopants, and stress effects to cause device contamination and failure. Nondestructive metrology techniques that rapidly and noninvasively screen for defects and relate silicon device structure to device performance are of value. We describe the first use of a liquid crystal tunable filter (LCTF) Raman chemical imaging microscope to assess the crystallinity of silicon semiconductor integrated circuits in a rapid and nondestructive manner without the need for sample preparation. The instrument has demonstrated lateral spatial resolving power of better than 250 nm and is equipped with a tunable imaging spectrometer having a spectral bandpass of 7.6 cm-1. The instrument rapidly produces high-definition Raman images where each image pixel contains a high-quality Raman spectrum. When combined with powerful processing strategies, the Raman chemical imaging system has demonstrated spectral resolving power of 0.03 cm-1 in a test silicon semiconductor wafer fabricated by using ion implantation. In addition, we have applied Raman chemical imaging for volumetric Raman imaging by analyzing the surface distribution of polycrystalline thin film structures. The approaches described here for the first time are generally applicable to the nondestructive metrology of silicon and compound semiconductor devices.
The scanning near-field optical probe technique has made it possible to perform conventional optical spectroscopies with unprecedented spatial resolution. We present the development of an instrument for scanning near-field Raman spectroscopy and present near-field Raman linescans and spectra of a range of materials with subwavelength resolution.
Raman spectra have been measured for a number of nitrates, nitrites, sulfates, ferrocyanides, and ferricyanides, both in the solid phase and in aqueous solution. Accurate locations of peak maxima are given. Limits of detection for some of the compounds are given for solutions and for solid mixtures in NaNO3. Preliminary measurements have been made on core material recovered from the storage tanks on the Hanford site in Richland, Washington. Representative spectra are presented, showing that it is possible to observe responses of individual components from measurements made directly on untreated cores, with the use of a fiber-optic sampling probe.
Methodology for in situ infrared monitoring and analysis of solid-phase organic reactions has been developed. The real-time, single-bead capabilities of this technique are illustrated through the analysis of solvent diffusion into, and subsequent wash-out from, a 70-μm aminomethyl polystyrene bead. This report further illustrates application of this technology for solid-phase synthesis with real-time analysis using two example reactions. Analytical hardware and the inherent benefits of real-time analysis with respect to precursor referencing and the quality, utility, and interpretation of the infrared data are also discussed.
We demonstrate the use of Raman microscopy for leak detection in hermetically sealed micromachined accelerometers. Leaks were indicated by the presence of a foreign gas, in this case oxygen, in the 70- mu m-deep cavity enclosing the accelerometer between a silicon cap and a Pyrex window. Confocal, nondiffraction-limited operation of the Raman microscope utilized the available pathlength in the sample while still rejecting most of the fluorescence from the Pyrex . Raman peak intensities were accurately determined in the presence of noise by fitting the spectra to a function that modeled the unresolved Q-branch line shapes of oxygen and nitrogen.
The usual laser employed for Fourier transform Raman spectroscopy is a Nd:YAG unit lasing at 1.064 μm. In this work, use of the 1.339-μm lasing emission from Nd:YAG has been demonstrated. The sensitivity of this instrument is comparable to that of conventional FT-Raman instruments, and excellent anti-Stokes spectra can be easily obtained. Operation further into the near-infrared offers additional possibilities for fluorescence minimization. Results are shown for copper phthalocyanine.
The feasibility of a direct quantitative analysis of styrene by Raman spectroscopy during an emulsion polymerization is examined. A dispersive spectrometer fitted with an intensified diode array detector is used with excitation from the 514.5-nm line of an Ar-ion laser. The limits of detection are 0.26 weight percent styrene in the reaction mixture. Raman measurements are compared with those obtained by UV absorption measurements on extracted samples and found to give essentially the same results.
A quantitative comparison of Raman and Fourier transform near-infrared (FT-NIR) spectroscopic techniques for the analysis of epoxy curing is performed. It is shown that the Raman technique yields a linear calibration curve much like FT-NIR. Band assignments in the Raman spectrum of diglycidyl ether of bisphenol-A (DGEBA) were performed by studying Raman spectra of smaller model compounds.
Fourier transform (FT)-Raman spectroscopy has been applied to the online analysis and control of a PCI3 reactor. This particular analytical technique was selected from a consideration of the Raman scattering efficiencies of the constituents of the reaction and the ability of the fiberoptic-coupled, near-IR, FT-Raman systems to remotely sample the toxic and potentially hazardous reaction mixture. In this communication we describe the Raman spectra of P4, PCl3, PCl5, and P4 dissolved in PCl3, as well as related compounds, along with relative band intensities of the constituents of the reaction. Factors leading to the optimum FT-Raman configuration for this particular process control problem are discussed in detail.
The potential of Raman microscopy for the examination of phase structure and composition of polymer blends is described. Provided that highly efficient collection optics are used, together with a CCD camera detector, the common problems of specimen heating and fluorescence can be reduced by the use of a relatively low-power (25mW) HeNe laser. For thin (<5 μm) film specimens, submicron morphological features can be resolved and phase compositions determined. For thicker specimens, the sampling depth controls the spatial resolution, but micron-scale morphological features can be imaged. When the microscope is operated in the spectroscopic mode, the use of an intermediate slit permits essentially confocal operation and can reduce the sampling diameter to about one micron. In cases where the image is inadequate, such as for thick or highly scattering specimens, phase sizes may be estimated by collecting several spectra at random on the specimen surface and determining the apparent scatter in blend composition. When the phases are large in comparison to the sampling volume, the composition data will be highly scattered. When the phases are small, then all measured compositions should be close to the average. The technique is illustrated with the use of a rubber-toughened epoxy resin, a polyethylene-polypropylene blend, and a polyester (PET/PBT) blend.
Analytical instrumentation, especially Near Infrared (NIR), and Gas Chromatography (GC) has been applied for a considerable number of years to the monitor and control of chemical manufacturing processes. By measuring the chemical species at the time and place of manufacture it becomes possible to modify the quantities of feedstock and the physical conditions, either manually or automatically, in order to improve the efficiency of the process and/or the quality of the product.While the information content of Raman spectra was always attractive for this type of application, implementation of Raman instrumentation was impractical until the last several years. The evolution of Raman instrumentation in the last 5 years, as well as the implementation of the mathematical data treatments that provide the needed quantitative information will be reviewed. Applications that are in the public domain will be described. This includes monitoring quality of hard carbon coatings on computer hard discs, chemical composition (mixtures, solvent separations, reactions such as polymerization, hydrogenation and curing etc.), gas composition, fermentation, polymorphy in pharmaceuticals, and polymer morphology. Rather than attempting to be exhaustive, the topics and literature covered will be selective - we will attempt to describe the state-of-the-art of a rapidly developing field, and give a sense of its potential.
The self-absorption effect is described and is considered in terms of how it might be expected to effect near-infrared Raman experiments. Experiments are detailed which dramatically demonstrate self-absorption in tetrahydrofuran. The results of these experiments are applied to some recently published unexplained observations, and it is thought that these observations may be fully explained by the self-absorption phenomenon. Discussion is presented of how to recognize and avoid or minimize self-absorption in quantitative Fourier transform Raman measurements.
The laser Raman and the Fourier transform infra-red (FTi.r.) microspectroscopic analyses were conducted to monitor the interfacial degradation process in a model composite of an aramid fibre (Kevlar 49) and unsaturated polyester (UP) exposed to water at 30 and 90°C. For micro-laser Raman spectroscopy, a single long fibre was embedded in the UP resin being subjected to static tension. Removing the applied tension after curing the film specimen introduced the residual tensile stress into the fibre. The progress of degradation by water in a region of interface was monitored by measuring the peak shift of the Raman spectrum varying proportionally to the stress generated in the fibre. The micro-FTi.r. measurements were done to examine the quantity and the state of absorbed water in the UP resin very near the interface. The thin film specimen, in which the long fibre was not subjected to pre-tension during the cure, was analysed under transmission mode. The residual tensile stress in the fibre was monotonously decreased in hot water at 90°C, and completely released for about 150h, although the stress reduction for early period of 24h was mainly caused by the relaxation of elastic modulus of the UP matrix. In water at 30°C, on the contrary, the residual stress remained the initial value for a long time above 1000h. The micro-FTi.r. analyses revealed that at an early stage the isolated water is mainly observed, and then larger amount of clustered water is absorbed with increasing soaking time, particularly at 90°C. At present, however, it is not clear which type of water more strongly participates in the interfacial degradation.
Studies have been made of the Raman spectrum of a poly(ethylene terephthalate) melt being extruded through a glass die. The effects observed in the spectrum are interpreted in terms of changes in molecular shape which vary with shear rate and melt temperature.
The use of interferometric instruments and excitation of samples with near-infrared light to obtain Raman spectra has established itself as a very useful technique. The main advantage, besides the relative simplicity of this approach, is the absence of the intense fluorescence background very often encountered with dispersive instruments when one is using visible light for excitation, mainly for organic samples.
Fast and exact identification of a great number of microorganisms is becoming a serious challenge. Differentiation and identification of microorganisms is today mainly achieved by the use of a variety of distinct techniques based on morphological, serological aspects and a set of biochemical test. Vibrational spectroscopic techniques can be complementary and useful methods in this field due to their rapidity, 'fingerprinting' capabilities, and the molecular information that they can provide. Using SERS at Ag colloids, we have conducted pilot studies to rapidly detect and identify bacterial clinical strains. Using a Raman microspectrometer equipped with a He/Ne laser, a first attempt to record SERS spectra was made on colloidal solutions. Spectra were of good quality but not very reproducible due to the movement of the microorganisms. Strains were then put in presence of Ag colloids and direct on-plate analysis was performed. Spectra were more reproducible, with diminished fluorescence, and reveal characteristic cellular-level information. Different growth conditions and colloid preparations have been tested. Pseudomonas aeruginosa and Escherichia coli clinical strains, responsible for nosocomial infections, have been our first test samples. An attempt has also been made to record SERS data from gold colloids in view of future measurement in the near-IR. Spectroscopic data are compared with ATR-FTIR results.
A method for real-time determination of the percent cure of epoxies via in situ fiber-optic Raman spectroscopy has been developed. This method utilizes a probe design developed for real-time monitoring of polymer curing and multivariate analysis to interpret the data and determine percent cure. This method was demonstrated to be reliable to +/-0.54% of cure in laboratory samples over a 50-99% cure range. A preliminary study measuring cure percentage in an industrial, glass-reinforced composite has been shown to be reliable to +/-0.82% in the 40-90% cure range.
Fiber optics were used to interface a Raman spectrometer to a long (1 m) sample tube, with the objective being increased sensitivity. Internal reflection of the laser light and the Raman scatter within the sample tube permitted a long solution length to be sampled, increasing the Raman sensitivity by factors of 30-50 over conventional capillary tube sampling systems. In addition, the sample was subjected to much lower power densities than with systems employing a focused beam, thus minimizing radiation damage. Detection limits of 10−9 to 10−8 M were achieved for resonance Raman scatterers, and normal Raman scatterers could be detected at the 1 × 10−5 M level.
Published Raman spectra are rarely corrected for variations in spectrometer sensitivity across the Raman spectrum, which leads to often severe distortion of relative peak intensities that impede cal- ibration transfer and library searching. A method was developed that uses the known luminescence of standards whichuoresce in response to laser irradiation. Since the standards are observed with the same sampling geometry as the Raman sample of interest, their spectra are subject to the same instrumental response function. Af- ter one-time calibration of the standards' ¯ uorescence output against a known tungsten source, the unknown Raman spectrum may be corrected for instrumental response by a simple formula. In practice, the user need only run the standard under the same conditions as the Raman sample, then apply a short GRAMS al- gorithm. The approach is demonstrated for coumarin 540a and Kopp 2412 glass standards, with 514.5- and 785-nm laser light, re- spectively. Once the corrected spectrum is in hand, the absolute Raman cross section of a given Raman feature may be determined by comparison to known scatterers such as benzene. Index Headings: Raman; Calibration; Intensity; Instrument re- sponse function.
Four different FTIR methodssingle-bead FTIR, beam condenser, macro attenuated total reflection (macro-ATR), and KBr pellet methodsand macro and single-bead FT Raman methods have been investigated, and the relative utility was compared for the analysis of resin-bound organic compounds and the monitoring of solid-phase organic reactions. Furthermore, the comparison includes two additional methods from the literature: diffuse reflectance infrared Fourier transform spectroscopy and photoacoustic spectroscopy. While all of these methods have some utility for solid-phase sample analysis, the relative merits of these methods vary particularly in such areas as the information content, spectral quality, sensitivity, speed, sample requirement, and the instrument cost. Both single-bead FTIR and beam condenser FTIR methods have been found to be superb methods in each of these aspects. In the following way, these methods meet many of the essential requirements for a thin layer chromatography (TLC) equivalent for solid-phase synthesis: (1) Only a single bead or 50−100 beads are needed for analysis so that reaction is not interrupted and is monitored in real-time. (2) A high-quality spectrum can be recorded within a few minutes. (3) No sample preparation is required, making the analysis time even shorter than that for TLC analysis. (4) These two FTIR methods provide qualitative, quantitative (the percentage of conversion), and kinetics information on organic reactions carried out on resin supports. Finally, from the synthetic chemist's point of view, the additional advantages of the beam condenser method, such as the low cost and the ease of operation, make it a more suitable choice as a TLC equivalent for solid-phase organic synthesis applications.
Methyl red, cresol red, and 4-pyridinethiol were examined for their ability to determine the pH at a surface. Methyl red and cresol red were coupled to cystamine. This produced a disulfide derivatized indicator which formed robust monolayers on sliver substrates. The spectroscopic technique used to examine these compounds was surface-enhanced Raman spectroscopy. We determined that all of these compounds possessed surface-enhanced Raman bands which were characteristic of the molecular structure associated with the indicator and its conjugate acid. Methyl red represents a near resonance indicator. It showed a linear log (I 1400/I 1615) vs pH relationship from pH 2 to 4.5. Some interference due to buff er anions was observed. Cresol red was examined as a resonance Raman indicator. Its linear range was pH 2-8 for the ratio of I 1600/I 1390. An inflection In the calibration curve was observed near pH 5. Cresol red was tested on an optical fiber for Its usefulness as a remote pH probe. It functioned very well and was used to follow a flowing, pH gradient produced by adjusting a reservoir pH with acetic acid. 4-Pyridinethiol is a normal Raman indicator. It possessed a linear log (I 1005/I 1100) vs pH relationship between pH 5 and pH 9. The calibration curves, including the inflection in the case of cresol red, are explained with Gouy-Chapman-Stern theory.
A variety of applications of the technique of Fourier transform (FT) Raman spectroscopy using a near-infrared laser excitation source have now begun to emerge. The design and construction of a bench-top, analytical-grade FT Raman spectrometer are described. Its specifications are explained and its performance and convenience of use are reported. A variety of analytical applications of the FT Raman technique have been surveyed to demonstrate the versatility of the spectrometer.
Several resins generically known as ‘dragon’s blood’ from different botanical and geographical sources were characterised non-destructively using Fourier transform Raman spectroscopy. Genuine ‘dragon’s blood’ resin (Dracaena spp.) as found on Socotra Island was the probable source in antiquity. The spectra of recently collected Socotran resins from different sites were compared with fresh ‘dragon’s blood’ resins from Aden and Australia and a commercial source of Daemonorops draco from south-east Asia. All resin samples were freshly collected. A means of identification of the resins from their Raman spectra is proposed. © 1997 by John Wiley & Sons, Ltd.
The first Raman spectroscopic analysis of coloured frescoes from the thirteenth century Convento de la Peregrina, Sahagun, Léon, Spain is reported. These frescoes were discovered only in 1956 after the church was re-opened after being sealed in the fifteenth century. The pigments were also confirmed by x-ray diffraction analyses. The red pigments are iron(III) oxide (haematite), cinnabar and a mixture of cinnabar and red lead (lead tetraoxide). The discovery of red lead, in particular, is of great interest as historical records recognize the known instability of this pigment mixture in adulterated samples. The black pigment is lamp-black or soot; black particles were also found in some red-pigmented painted areas, which are attributed to contamination from candles or oil-lamps either at the painting stage or during religious services. Copyright © 1999 John Wiley & Sons, Ltd.