forensic and homeland security applications of modern portable raman spectroscopy laura fairburn...
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Forensic and homeland security applications of modern portable Raman
spectroscopyLaura Fairburn
Mike Rusak
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Summary of the Paper
• Applications in forensics and homeland security, including field testing for chemical and biological warfare agents
• Subtypes of Raman Discussed:
• Convential Raman Spectroscopy
• Resonance enhanced
• Spatially offset (SORS)
• Surface Enhancement (SERS)
• can be coupled with Stand-Off Raman Detection
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Raman Spectroscopy
• measures the scattering of monochromatic light caused by the sample
• most of the light reflects off the sample at the same wavelength, while some light does scatter at different wavelengths
• this is caused by an interaction with a phonon, which causes the laser to gain or lose energy
• From that, information about the phonon mode is supplied, from which we can determine similarly to FT-IR what functional groups are in the compound.
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Raman Spectroscopy’s Drawbacks
• Specific structure can’t be determined
• should be used as a last step analysis, not first on site technique
• Not very Powerful
• One photon in 108 photons will exhibit Raman scattering
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•Mixtures drastically complex the spectra, therefore sample preparation may be needed
•Because of the high intensity laser used, dark coloured explosives have been known to heat up.
• In some causes, it has even caused ignition
Drawbacks Cont.d
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Drawbacks Cont.d
• Very expensive compared to other more commonly used instruments
• double monochromators and laser sources make it more expensive compared to other instruments
• Fluorescence can be a large problem
• Especially in the visible and UV regions
• Slight impurities in compound may fluoresce, complicating the spectrum
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• If the intensity of the wavelength is too high, such as when a UV laser is used, the sample may thermally decompose.
• the most modest of lasers have been known to cause band shifts in the Raman Spectra
Drawbacks Cont.d
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Potential Questions
•There were some questioned to be asked after reading this article.
•What will happen if the material you’re scanning through is Raman active?
• Is there a library of spectra for all known biological hazardous agents?
• Is this really the best technique for the job it’s required to do?
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Conclusion
•Raman Spectroscopy is undeniably useful in the same way as infrared spectroscopy in a chemistry lab, but it is not routinely used in a forensic setting. Therefore, why use it when concrete techniques are can be used instead? Eg) GC-MS, ion mobility spectrometry, etc.