Raman Spectroscopy

Colin Campbell discusses his work applying SERS to biomedical applications.

Our annual review of products introduced at Pittcon or during the previous year, broken down by the following categories: accessories, atomic spectroscopy, components, imaging, mass spectrometry, mid-IR, NIR, NMR, Raman, software, UV-vis, and X-ray.

In recent years, Raman spectroscopy has been applied to process monitoring and control applications in a wide range of application fields, including bioprocessing, pharmaceuticals, food, oil and gas, and oceanography. Brian Marquardt, cofounder and CEO of MarqMetrix, Inc., and director and senior principal engineer with the Center for Process Analysis and Control in the Applied Physics Laboratory at the University of Washington, has more than 15 years of experience with such applications and recently spoke with us about his research.

Matthew Baker, a senior lecturer in chemistry at the University of Strathclyde, in Glasgow, has won the inaugural Emerging Leader in Molecular Spectroscopy Award, which is sponsored by Spectroscopy magazine. This new 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 Baker at the SciX 2016 conference in September, where he will give a plenary lecture and be honored in an award symposium.

Were it not for the problem of photoluminescence, only one laser excitation wavelength would be necessary to perform Raman spectroscopy. Here, we examine the problem of photoluminescence from the material being analyzed and the substrate on which it is supported. Selecting an excitation wavelength that does not generate photoluminescence reduces the noise level and yields a Raman spectrum with a superior signal-to-noise ratio. Furthermore, we discuss the phenomenon of resonance Raman spectroscopy and the effect that laser excitation wavelength has on the Raman spectrum.

The use of Raman spectroscopy to produce material images whose contrast is derived from chemical or crystallographic species has been seen as quite useful since the introduction of the Raman microscope in 1976, but particularly, more recently, with the development of more sensitive and easier-to-use instruments. When the various species in the field of view have spectra with non-overlapping analytical bands, simple univariate analysis can provide good images. When overlapping bands are present, multivariate techniques, especially MCR (Multivariate Curve Resolution), have been successfully applied. However, there are cases where even MCR results may be problematic. We will look at some maps of a ceramic composite containing SiC, Si, B4C, and Carbon, where each of these species has non-unique spectra to see what type of results flexible software can produce. What is the goal in this type of exercise? For some of us, creating images is like a teenager’s computer game. But really what we are trying to do is to extract information about a sample from its Raman image. A beautiful rendition is nice, but it must yield information. The following will show how Raman maps can provide useful information on a sample.

Crystallinity is an important factor when producing pharmaceuticals as it directly affects the bioavailability of the drug. Low frequency Raman spectroscopy offers some advantages to the detection and analysis of crystallinity in pharmaceutical samples. Here the experimental requirements for low frequency Raman measurements are described. The application to the study of crystallinity with a number of examples is discussed and the advantages and limitations of this technique are highlighted and compared with other techniques.

In this paper, we demonstrate a sensitive surface-enhanced Raman spectroscopy (SERS) substrate for trace dimethoate detection. The substrate is composed of Ag nanoparticle/probe/smooth Au film stack configuration. The nanogap formed by an Ag nanoparticle and a macroscopically flat Au film is one kind of “hot site” which will dramatically increase the total “hot spots” number.

Imaging techniques using vibrational spectroscopy, mass spectrometry (MS), and atomic force microscopy have all been advancing and gaining momentum in recent years. There is great potential power in these imaging techniques, particularly in the biomedical field. Thomas Bocklitz of at the Friedrich-Schiller-University Jena is working to better harness the power of these techniques by combining them.

Attend any conference covering vibrational spectroscopy, and you will likely hear numerous talks about developments in tip enhanced Raman scattering (TERS) and surface-enhanced Raman scattering (SERS). Both approaches hold exciting promise, but face significant challenges as well. We asked a panel of Raman experts about the current and future role of these two approaches.

The application note explains how the Raman Spectroscopy can be helpful in the analysis of cathodes and anodes in Li-ion batteries.

Statistical and morphological analysis of particles on a filter has been complemented by chemical analysis based on Raman spectroscopy using the ParticleFinder tool, allowing further insight into the particle composition and its origin within a production line.

Evaluation of the discrimination power of Raman spectroscopy in decreasing turnaround time in clinical diagnosis, when analyzing microcolonies from nine bacterial and one yeast species directly on solid culture medium after a shortened incubation time.

Recent reports of the successful use of Raman spectroscopy for important biomedical applications are quite exciting. These applications include imaging for disease diagnosis, including significant improvements for endoscopic probes, and identification of microorganisms. But is it truly practical and feasible to implement Raman technologies in a clinical environment?

Imaging techniques using vibrational spectroscopy, mass spectrometry (MS), and atomic force microscopy have all been advancing and gaining momentum in recent years. There is great potential power in these imaging techniques, particularly in the biomedical field. Thomas Bocklitz of at the Friedrich-Schiller-University Jena is working to better harness the power of these techniques by combining them.

In honor of Spectroscopy's celebration of 30 years covering the latest developments in materials analysis, we asked a panel of experts to assess the current state of the art of Raman spectroscopy and to try to predict how the technology will develop in the future.

Locate particles, generate size/shape statistics, select particles based on size/shape, and acquire Raman spectra. Easily locate and identify particulate matter, including pharmaceutical materials, trace forensic evidence, geological rock/mineral particles, and airborne contaminants trapped on filters

Demonstrates uRaman from TechnoSpex Pte. Ltd. is a promising instrument to determine the quality of the transferred single layered graphene on a 300-nm silicon dioxide (SiO2) substrate.

 Resonance and off-resonance Raman spectroscopy and imaging are used to examine the spatial variation of the solid-state structure and electronic character of few-layer MoS2 flakes. Simultaneous acquisition of photoluminescence spectra with the Raman scattering provides complementary ways of rendering Raman and photoluminescence spectral images of thin-film MoS2.

There are multiple circumstances where characterization of a collection of particles has value to analysts. In some environments, materials are plagued by particulate contamination that impacts product quality.

Segmented channel waveguides have been fabricated in single-crystal KTiOPO4 through a topotactic process of partial cation exchange. The ion-exchanged waveguides maintain the high nonlinear susceptibility of KTiOPO4 to function as frequency doubling laser light sources

Raman microscopy is a promising technique for visualizing the distribution of molecules in cells. However, along with the benefits come challenges. This interview with Katsumasa Fujita, an associate professor in the Department of Applied Physics at Osaka University in Osaka, Japan, discusses his use of this technique for the imaging of live cells.

A method for removing fluorescence-induced backgrounds from Raman spectra using sequentially shifted excitation (SSE) is described. The method uses a temperature-tuned, distributed Bragg reflector diode laser to produce the multiple excitation spectra required to implement the SSE algorithm. Examples applying the SSE method to analysis of motor oils and edible oils are given.

Metal oxides often occur in crystals where there are no molecular units. Here, we provide an introduction to the concepts that need to be understood when analyzing metal oxides in materials such as paint, ceramic pigments, corrosion films, catalysts, and minerals.