Emily Sonnex Identification of forged Bank of England £20 banknotes using IR spectroscopy

Infrared spectroscopy in Forensics FT-IR has been used for many forensic applications Infrared microscopy is a relatively new technique and currently has few forensic uses Perkin Elmer Spectrum 100 with Spotlight 400 imaging system attachment (Beaconsfield, UK) Figure 1. Perkin Elmer Spectrum 100 and Spotlight 400 FT-IR

Banknotes -Previous work Vila et al. (2006), used ATR FT-IR to distinguish between forged and genuine euro notes Distinct differences in spectra between the notes Little other work has been done in this field Is it possible to do the same with notes from the Bank of England and develop a method for their identification? Vila et al. Analytica Chemica Acta 559 (2006)

FT-IR of banknotes ATR attachment on a spectrum 100 Additional peaks in the forged notes Calcium carbonate 1400 cm -1 broad, stretching mode 879 and 715 cm -1 sharp, deformation mode Figure 2. FT-IR spectra of genuine (top) and forged (bottom) notes, paper area

Simplifying the process Nicolet IR 100 FT-IR by Fisher Scientific ‘spectrometer in a suitcase’ Identifying peak at 1400 cm -1 still present. Figure 3. FT-IR spectra of genuine (top) and forged (bottom) notes, paper area

Investigating other areas of the note The hologram section was also investigated Several subtle differences observed υ (OH) ~ 3500 cm -1 υ (C-H) ~ 2900 cm -1 υ (C=O) ~ 1740cm -1 Requires greater skill to identify differences in these peaks Figure 4. FT-IR spectra of genuine (top) and forged (bottom) notes, hologram area

Taking it further Spectrum 100 FT-IR with Spotlight 400 microscope attachment Spectral imaging with principle component analysis Mirrors the work of Villa et al. Figure 5. Visible image and spectral map of a banknote with corresponding spectra, Forged (left) and Genuine (right)

Looking forward The Bank of England has announced its intent to issue polymer banknotes from 2016 Australia is currently a large producer of polymer banknotes Most of their detectable forged notes are printed on paper Could the proposed method be extended to polymer notes even if the forgeries were printed on polymer?

FT-IR of polymer banknotes The polymer notes can be distinguished from other readily available polymers -Acetate -Polyethylene Figure 6. FT-IR spectra to compare genuine Australian banknote (top) Cellulose acetate (middle) Polyethylene (bottom)

Spectral mapping of polymer banknotes Spectral maps of polymer banknotes were recorded No spectral contrast seen other than black writing May see a contrast if forged notes were produced on polymer Figure 8. Visible image and spectral maps of an Australian banknote, Main body (left) and Black writing (right)

FT-IR of polymer banknotes The polymer notes have two distinct sections – a clear window and the rest of the note Both are distinctly different to forged paper notes Figure 9. FT-IR spectra to compare forged banknote (top) Australian banknote printed section (middle) Australian banknote clear window (bottom)

With thanks to…