Forensic and homeland security applications of modern portable Raman

spectroscopyLaura Fairburn

Mike Rusak

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

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.

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

•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

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

• 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

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?

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.