Special Issues-06-01-2008

Raman spectroscopy is going through a major revolution with the continuous introduction of new fiber-based modular systems for low-resolution applications. More and more scientists are discovering what Raman spectroscopy can do for their research, education, and commercial applications thanks to the low costs and flexibility this new technology is providing. New applications and prospects are presented each day, and it is important to understand the advantages and limitations that this user-friendly analytical technique can provide to address these opportunities with a scientific approach.

Over the last few years, Raman has made the transition from a technique used solely in a research environment to one that is now seen as a powerful tool for routine analytical use. Raman spectroscopy now is used widely for sample identification in fields as diverse as forensics, QA/QC, art conservation, defect analysis, and failure analysis. This has imposed new demands on the technique for reproducibility and stability. Successful sample identification takes advantage of the extensive spectral libraries and sophisticated search algorithms that have been developed in recent years. However, in order to be able to cross-correlate experimental and library spectra with any degree of confidence, it is critical that the Raman spectrometers used to collect the spectra are calibrated rigorously. It is likewise critical for QC applications that spectra collected on one instrument can be compared reliably with spectra collected on other instruments and that results remain constant when collected over extended periods..

Raman imaging has moved on. It is now possible to capitalize on the wealth of information available from a Raman spectrum by imaging materials over large areas, with the spatial resolution, spectral resolution, and laser excitation parameters tailored to suit each application. Raman experiments and images from a diverse range of samples are presented.

Chemical analysis in the forensic field is different in many aspects from other areas of analysis. The ultimate goal is to identify the sources of evidence, often by matching chemical composition. In this regard, identifying minor elements or trace impurities is as important as identifying main ingredients. In some cases, identifying minor and trace components can be critical to determining that material collected at the site of a crime is identical to material collected in a suspect's environment. In other cases, full identification of trace evidence can be important. Raman microscopy is capable of providing both types of information on minute amounts of material.

Since it was first described in 1974, surface-enhanced Raman spectrometry (SERS) has been thought to offer significant potential for a range of different applications. The theoretical sensitivity and specificity envisaged for this powerful technique has engaged scientists for many years, but practical challenges have hindered its routine adoption. Now, a new approach combines a robust and reliable substrate with expertise in surface chemistry and molecular biology on a platform that can be adapted for a wide variety of Raman instrumentation and customized routine applications.

The combination of confocal Raman and atomic force microscopes allows chemical and surface topography imaging of large samples without any ongoing process control by an operator. This article describes the relevant measurement principles and presents examples of automated measurements on nanostructured materials.