Raman Spectroscopy

The SERS signal arises from the combination of the number of molecules, the polarizability or cross-section of the molecule, and the electric field experienced by the molecules. Understanding how these variables interact to generate the SERS response is the key to applying SERS accurately.

Recent technical advances in biomedical Raman imaging pave a way to its application in the biomedical fields, where morphological information of samples provides rich information. A recent technical conference in Osaka, Japan, explored these developments.

Raman imaging provides detailed crystal orientation information for two-dimensional MoS2 prepared by chemical vapor deposition on silicon substrates. These two-dimensional crystals consist of individual atomic layers of sulfur, molybdenum, and sulfur atoms.

The Raman Terminology Guide you now have before you is a comprehensive set of definitions for topics of interest to molecular spectroscopists and those specifically using Raman spectroscopy in their daily work. This guide includes the types of Raman spectroscopy techniques and many terms related to the applications of Raman spectroscopy instruments. This terminology guide includes definitions for more than 250+ molecular spectroscopy terms in sufficient detail to provide readers with a reasonable understanding of the concepts covered.

Ping-Heng Tan of the Chinese Academy of Sciences is advancing the use of Raman spectroscopy to characterize graphene-based materials.

Raman 2D-COS spectral data provide information on conformational changes of polymers. Here, Raman spectra of ethylene vinyl acetate and vinyl acetate copolymer are measured and interpreted, enabling a description of morphological changes related to the vinyl acetate group.

Christy L. Haynes, of the University of Minnesota (Minneapolis and Saint Paul, Minnesota), has been working with her research team to explore the use of a rapid and facile technique to empirically screen affinity agents of diverse compositions for all manner of targets. Here, she describes the advantages of using isothermal titration calorimetry (ITC) for screening of polymer affinity agents for use with surface-enhanced Raman scattering (SERS).

Alignment of the instrument y-axis is a critical step for quantitative and qualitative measurements using spectroscopy. Here, we explain in detail how to use photometric standards for ultraviolet, visible, near infrared, infrared, and Raman spectroscopy.

Spectroscopy can be difficult to carry out outside a controlled laboratory environment. Imagine, then, the hurdles that would accompany performing spectroscopy in the extreme conditions of deep space or the ocean floor. Mike Angel, a professor of chemistry at the University of South Carolina, has taken on those challenges, working on new types of instruments for remote and in- situ laser spectroscopy, with a focus on deep-ocean, planetary, and homeland security applications of deep ultraviolet Raman, and laser-induced breakdown spectroscopy to develop the tools necessary to work within these extreme environments.

When stress is applied to an object, it can produce strain. Strain can be detected through changes in peak position and bandwidth in Raman spectra. Here, we show examples of how strain in technologically important materials appears in the Raman spectra.

By combining Raman spectra interpretation with rheometric measurements, molecular conversion from crystalline to amorphous structures for polymers is revealed.

Ishan Barman, PhD, an assistant professor at Johns Hopkins University, has won the 2019 Emerging Leader in Molecular Spectroscopy Award, which is presented by Spectroscopy magazine. This annual award recognizes the achievements and aspirations of a talented young molecular spectroscopist, selected by an independent scientific committee. The award will be presented to Barman at the SciX 2019 conference in October, where he will give a plenary lecture and be honored in an award symposium.

Significant progress is being made to harness the power of spectroscopy technique for medical research. An ongoing challenge, and area of development, in this effort, is to “see” more and more detail about biological activity, even within individual cells. Ji-Xin Cheng, a professor of biomedical engineering at Boston University, is advancing such work, by developing techniques like midinfrared photothermal (MIP) imaging and Raman spectromicroscopy. Cheng is the 2019 winner of the Ellis R. Lippincott Award, which is awarded annually by the Optical Society, the Coblentz Society, and the Society for Applied Spectroscopy, to an individual who has made significant contributions to the field of vibrational spectroscopy. Here, Cheng speaks to us about those techniques.

Five key qualitative factors–speed, sensitivity, resolution, modularity and upgradeability, and combinability–contribute to the quality of confocal Raman imaging microscopes. Using application examples, this article introduces modern Raman imaging and correlative imaging techniques, and presents state-of-the-art practice examples from polymer research, pharmaceutics, low-dimensional materials research, and life sciences.

A new application of surface-enhanced Raman spectroscopy (SERS) is described for quantifying low concentrations of pathogens with high reproducibility. In this novel assay, bacteria are captured and isolated using functionalized metal nanoparticles for rapid optical identification via SERS. Initial tests with a portable SERS system validated the ability to identify the presence of Escherichia coli and methicillin-resistant Staphylococcus aureus bacteria.

In this study, macro- and microscopic Raman spectroscopy were used to identify different commercial microplastic fibers using measured spectra with database searches. Raman microscopy is demonstrated as a powerful technique for microplastic fiber characterization, especially for samples that contain mixtures of components, including multiple polymers, or additives.

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Spectral changes revealed by two-dimensional correlation spectroscopy can be used to interpret structural changes in polymers determined by processing conditions, so that materials can be rationally engineered for particular applications with known mechanical requirements.

Duncan C. Krause, of the Department of Microbiology at the University of Georgia, discusses his group’s work to establish a SERS method with silver nanorod-array substrates for detecting the pathenogenic mycoplasma that causes bronchitis and pneumonia.

Igor K. Lednev, of the Department of Chemistry at the University at Albany, the StateUniversity of New York, has been developing the use of Raman spectroscopy for a varietyof forensic applications, including determining the age of blood stains and linking gunshot residues to specific ammunition–firearm combinations.

Two-dimensional (2D) Raman correlation spectroscopy is a powerful analytical technique for analyzing a system under the influence of an external perturbation. Isao Noda, of the Department of Materials Science and Engineering, at the University of Delaware and Danimer Scientific, has been developing 2D Raman correlation spectroscopy and applying it to the study of various materials, including exciting new biopolymers. He recently spoke to us about this work.

We show Raman spectra of polymeric fibers acquired as a function of increasing stress and temperature. With knowledge of Raman band assignments, it becomes possible to understand, in detail, the molecular changes that are responsible for polymer orientation and crystallization.

The Raman spectra of a particular face of a single crystal can be significantly different if acquired with different microscope objectives. This article explains the underlying physics of changes in relative intensity and even peak position of certain Raman bands depending on the microscope objective used to acquire the spectrum.

The apparent reaction kinetics between SO3 and polyethylene are investigated in various halogenated solvents using in situ Raman spectroscopy with an immersion Raman probe, demonstrating the power of in situ Raman spectroscopy to monitor hazardous reactions.

This study explores the use of a novel SERS substrate that can enhance the Raman signals of explosives that are present in picogram quantities in neat solutions using a visible laser wavelength and a compact Raman instrument.

The in situ combination of rheometry and Raman spectroscopy allows for real-time, synchronized measurement of both physical and chemical material properties.

A simple SERS-based method was used to identify low doses of the APIs alprazolam, codeine, oxycodone, and hydrocodone using a handheld Raman spectrometer.

A procedure was developed to calibrate the wavenumber (energy shift) axis in Raman spectrometers, and it was tested in both portable and laboratory-based instruments.

Interference from background fluorescence is a common challenge in Raman analysis. A study of three different types of biological samples was made to compare the ability of 785-nm and 1064-nm excitation to deal with this problem.