In situ surface enhanced resonance Raman scattering (SERRS) spectroscopy of biro inks--long-term stability of colloid treated samples.

The script produced by two black biro inks in 1998 in a document that was not subjected to any special storage conditions or further treatment was re-analysed by SERRS spectroscopy. The results presented show that the analyses of the areas of the ink strokes previously treated with an aggregating agent. poly-(L-lysine), and then silver colloid still produce strong SERRS spectra. No major changes are observed in the spectra thus still providing a method for discriminating between the two inks used in the document and illustrating the long-term stability of the colloid treatment. This ability to re-analyse the ink samples without any further treatment is attributed to the use of very fine pen nibs to apply the reagents.