Analysis of Forensic Evidence Using Raman and Infrared Microscopy

Infrared and Raman microscopy have become essential tools for complete forensic investigations. Bruker Optics offers infrared and Raman microscopes designed ad hoc for optimal forensic microanalysis. Thanks to the highly specific nature of infrared and Raman chemical analysis, the systems are able to identify unknown compound.

Raman and Infrared Microscopy Applications

Infrared microanalysis is ideal for drug and trace identification. Raman spectroscopy provides superior results for pigments, paint chips and other inorganic samples. It is also ideal for polymorphic analysis of drugs, fibers and other evidence substances. Raman encompasses the long wavelength region of the spectrum, where inorganic and solid state vibration modes occur. This region of the spectrum is difficult to access with infrared spectroscopy due to the high absorptivity of water.

Senterra Raman Microscope and Hyperion Infrared Microscope

Both the SENTERRA II Raman microscope (Fig. 1) and the HYPERION infrared microscope (Fig. 2) offer microscopy capabilities that complement the spectroscopic analysis. Optical analysis enables to identify the physical properties of the samples including color, shape, morphology, etc. The instruments also offer contrast enhancement tools, such as the aperture stop in the Kohler illumination beam path, visible polarizers, darkfield illumination, and fluorescence illumination. These facilitate the characterization and visualization of fibers, multilayer laminates, gun shot residues, paint chips and other evidence.

Figure 1. Senterra Raman microscope.

Figure 2. TENSOR 27 FT-IR Spectrometer with HYPERION 3000 FT-IR Microscope.

• The visual images are captured and stored in the OPUS software that is GLP and 21CFR part 11 compliant. No manipulation of the original data or images is possible. Copies of the original data may be made and modified, but this action and any others are recorded to guarantee a secure data trail.
• After storing the optical properties of the evidence, the infrared spectra are collected using the Hyperion microscope in the appropriate transmission, reflection or ATR modes of acquisition. Fibers are typically studied via transmission or ATR.
• Library searching (proprietary ATR Synthetic and Natural Fiber Libraries) of the spectra offers quick and precise identification. The minimum sample size that can be investigated is limited only by diffraction. Fibers less than 8 µm diameter are readily studied by transmission and ATR.
• Gun powders are quickly and directly identified by Raman or ATR infrared spectroscopy. Raman spectroscopy is especially useful for paint chips, since the spectroscopic response of inorganic pigments and solid state modes is readily available.
• Further, the Senterra uses a patented confocal design that enables quick and direct data collection of drugs and other evidence through polymeric bags. The Senterra utilizes SureCal, a proprietary wavelength calibration method to ensure intuitive and easy data collection.
• Paint chips and polymer multilayer laminated samples can as well be easily studied using infrared or Raman imaging. A visible picture of the sample can be promptly correlated to its corresponding infrared or Raman image. Infrared and Raman imaging are conducted by point-by-point mapping. Full-field infrared imaging can also be conducted using a focal-plane-array detector (FPA). More than 4000 spectra/s can be collected with the HYPERIONyperion using the FPA detector. Finally, Raman depth profile images are also easily collected using the intuitive OPUS/Video software.

This information has been sourced, reviewed and adapted from materials provided by Bruker Optics.

For more information on this source, please visit Bruker Optics.