SERRS technology enhances Raman spectrometer for document examination

Raman spectroscopy is a new exciting technique with a potentially valuable contribution to make to the science of questioned document examination. A Raman spectrum contains numerous peaks that correspond to the molecular structure of the material examined and chemically different inks are likely to show variations in their spectra even when they cannot be differentiated by any other means. The analysis is rapid, easy to use and may be carried out on inks in situ, which makes it ideal for use on a day to day basis.

However, a number of materials are not readily suited to conventional Raman spectroscopic examination. These include inks that fluoresce in the same spectral range as their Raman emission; the fluorescence signal is often a million times greater than the Raman signal so that the useful Raman spectrum is masked overwhelmingly . Fortunately, a simple solution is available. Called Surface Enhanced Resonant Raman Scattering (SERRS), it will quench fluorescence and enhance the useful Raman signal.

Fortunately the 'SERRS' technique is simple to perform and preserves the convenience of the examination technique. In practice, an aggregating agent, poly-L-lysine, is applied to a small sample of the ink on the document which, once dry, is itself treated with a colloidal silver preparation. Both applications are carried out with a simple applicator such as a mapping pen. Once the final application is dry the sample is examined with a Raman spectrometer in the normal way. The effect is often dramatic, the interfering fluorescence disappears leaving the detailed Raman spectrum for examination. Both the SERRS preparations are supplied by Foster & Freeman and have a long shelf life.

The SERRS technique provides spectacular results and without doubt extends the effectiveness of Raman spectroscopy as a means of differentiating inks. A full SERRS kit containing reagents and applicators is supplied, as standard, with the Foram 685, the company's Raman spectrometer.

For a full report on recent research carried out into the effectiveness of Raman spectroscopy and SERRS by Foster & Freeman please contact our Sales department.

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