Surface Enhanced Raman Scattering (SERS) for Characterization of Inks for Cultural Heritage and Forensic Applications

Daniela IACOPINO, Tyndall National Institute University College Cork, Cork, Ireland

Identification of inks’ formulations and elucidation of processes leading to color fading are exceedingly important for dating, active conservation and long-term preservation of paper artworks. Dyes and pigments in inks can be difficult to identify, due to the presence of other chemicals in the mixture and patent protection. Recently Surface Enhanced Raman scattering (SERS) has been identified as suitable spectroscopic technique. Blue and black inks in ballpoint pens were identified with the use of silver colloidal solutions. However, SERS spectra had to be taken within 10 min of colloid deposition due to fast silver oxidation. Additionally, chemical treatment of the colloidal solution had to be carried out.

In this work we have prepared a number of metal nanostructured SERS probes based on metal nanoparticle suspensions, metal nanoparticle arrays and metal-evaporated polymer surfaces. The variety of SERS materials allowed either in situ and ex situ analysis of inks contained in BIC pens and Stabilo felt tip pens thus allowing to collect information on ink composition and its interaction with paper matrices. Two excitation wavelengths at 514 nm and 785 nm were used. Comparison between Normal Raman (NR) spectra and SERS spectra showed high enhancement factors attributed to an electromagnetic effect generated by the use of metal nanostructures in plasmonic resonance with the excitation wavelengths.

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