Raman Spectroscopy

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.

Our annual review of products introduced at Pittcon or during the previous year

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.

The resonance Raman spectra of carotenoids vary with subtle changes on the functional side groups, making these spectra useful for identifying and characterizing carotenoids.

A straightforward numerical approach to estimate the performance of a spatial filter in Raman backscattering spectroscopy has been developed. This approach enabled the authors to determine an optimal hole diameter that balances spatial resolution and signal intensity.

The Raman spectra of crystalline and amorphous solids of the same chemical composition can be significantly different primarily because of the presence or absence of spatial order and long range translational symmetry, respectively. The purpose or goal of this installment of Molecular Spectroscopy Workbench is to help readers understand the underlying physics that affect the Raman spectra of crystalline and amorphous solids. Wave vector, reciprocal space, and the Brillouin zone are explained with respect to Raman spectroscopy of solids.

In biomedical applications of surface-enhanced Raman spectroscopy (SERS), nanoparticles can enhance the Raman signal and provide additional functionality. Duncan Graham of the University of Strathclyde has been pushing the limits of what can be achieved using functionalized nanoparticles and SERS, in applications such as cholera detection, lipid profiling in cancer cells, and assessing the efficacy of anti-cancer drugs, For this and other work he has won the 2017 Charles Mann Award, presented by the Federation of Analytical Chemistry and Spectroscopy Societies (FACSS). He recently spoke to Spectroscopy about this work. This interview is part of a series of interviews with the winners of awards that will be presented at the SciX 2017 conference in October.

Portable instrumentation for Raman spectroscopy has rapidly evolved over the last decade, where sample testing that once occurred in the laboratory is now executed in the field (e.g. warehouse).   Portable Raman spectroscopy is a powerful technique for the rapid identification of diversely sourced raw materials used in pharmaceutical processing.  In addition to portability; reduced cost, rapid data acquisition and ease of use make this powerful technique attractive and accessible to both expert spectroscopists and non-specialists.  In most cases, the method development can be easily accomplished in the laboratory after which the instrument and methods are transferred to field for sample analysis or warehouse areas for inspection of incoming raw material.  Qualitative Raman methods for identification of raw materials typically utilize spectral libraries for sample to standard comparison.  When developing Raman spectral libraries for raw material identification, great care is required when considering critical factors (e.g. instrument type, Raman capability, container type, container interference, background interference, material variability) that can potentially influence the identity of the material.  This paper discusses portable Raman techniques and approaches for raw material identification, as well as key considerations for developing and validating Raman spectral libraries.

Controlling the orientation of the laser and Raman polarization relative to the sample orientation can provide a wealth of information in the Raman spectrum that would be difficult to achieve by other methods. Presentation of the spectra makes these effects appear straightforward, but because of multiple instrumental factors, and experimental design, it is easy to produce erroneous results. This column is going to explain what instrumental components affect the polarization effects that are observed, and how the sample setup itself affects the Raman signal.

Heinz W. Siesler, Emeritus Professor at University of Duisburg-Essen, reviews Jerry Workman’s new book, The Concise Handbook of Analytical Spectroscopy Theory, Applications, and Reference Materials

Raman spectroscopy can be used to determine the temperature of a material when other more direct means are either impractical or not possible. The material’s temperature can affect the peak position of Raman bands. When a Raman band shifts significantly with temperature, the monitoring of the peak position can be the most straightforward manner of determining temperature provided the Raman spectrometer has sufficient spectral resolution. Another method is to determine the temperature from the ratio of the Stokes and anti-Stokes signal strengths of a given Raman band. The latter method requires the ability to detect light at wavelengths longer and shorter than that of the laser and an accurate measurement of the wavelength dependent instrument response function.

When characterizing microscale objects using a Raman microscope, certain basic practical aspects of analytical instrument performance and experimental design should be taken into consideration.

The accurate determination of protein structure is integral to the medical and pharmaceutical communities’ ability to understand disease, and develop drugs. Current techniques (CD, IR, Raman) for protein structure prediction provide results that can be poorly resolved, while high resolution techniques (NMR, X-ray crystallography) can be both costly and time-consuming. This work proposes the use of drop coat deposition confocal Raman spectroscopy (DCDCR), coupled with peak fitting of the Amide I spectral region (1620–1720 cm-1) for the accurate determination of protein secondary structure. Studies conducted on BSA and ovalbumin show that the predictions of secondary structure content within 1% of representative crystal structure data is possible for model proteins. The results clearly demonstrate that DCDCR has the potential to be effectively used to obtain accurate secondary structure distributions for proteins.