Surface-enhanced Raman scattering (SERS) was investigated for applications in the analysis of anthraquinone dyes used in works of art. Two SERS procedures were developed and evaluated with three frequently used anthraquinone dyes, alizarin, carminic acid and lac dye. The first procedure involves coating a layer of silver nanoparticles directly on pieces of filter paper stained with the dyes of interest by thermal evaporation to induce SERS effect. In the second procedure, a SERS-active Ag-Al 2 O 3 substrate was prepared by spin-coating an alumina-nanoparticle layer onto a glass slide to provide the nanostructure of the substrate, followed by thermally evaporating a layer of silver nanoparticles on top of the alumina layer. Aliquots of dye solutions were delivered onto this substrate to be analyzed. Intense SERS spectra characteristic of alizarin, carminic acid and lac dye were obtained using both SERS procedures. The effects of two parameters, the concentration of the alumina suspension and the thickness of the silver nanoparticle layer on the performance of the Ag-Al 2 O 3 substrate were examined with alizarin as the model compound. Comparative studies were conducted between the Ag-Al 2 O 3 substrate and the SERS substrate prepared using Tollens reaction. The Ag-Al 2 O 3 substrate was shown to offer larger enhancement and improved reproducibility than the Tollens substrates. Finally, the potential applicability of the Ag-Al 2 O 3 substrate for the analysis of real artifact objects was illustrated by the identification of alizarin extracted from a small piece of textile dyed using traditional methods and materials. The limit of detection for alizarin was estimated to be 7 × 10 −15 g from tests performed on solutions of known concentration.

No abstract

Surface-enhanced Raman scattering (SERS) was investigated for applications in the analysis of anthraquinone dyes used in works of art. Two SERS procedures were developed and evaluated with frequently used anthraquinone dyes, alizarin, carminic acid and lac dye. The first procedure involves the removal of a microscopic fragment containing alizarin from a painting, and a layer of silver nanoparticles was thermally evaporated directly on the fragment to induce SERS signal from alizarin. The applicability of this procedure for analyzing solid samples of color layer from paintings was discussed in detail. In the second procedure, a SERS-active substrate was prepared by spin-coating an alumina-nanoparticle layer onto a glass slide, followed by thermally evaporating a layer of silver nanoparticles on top of the alumina layer. Aliquots of dye solutions were delivered onto this substrate where intense SERS spectra characteristic of alizarin, carminic acid, and lac dye were obtained. The effects of two parameters, the concentration of the alumina suspension, and the thickness of the silver nanoparticle layer, on the performance of the Ag-Al 2 O 3 substrate were examined with alizarin as the model compound. Comparative studies with other common SERS substrates showed larger enhancement and improved reproducibility for the Ag-Al 2 O 3 substrate. The potential applicability of the Ag-Al 2 O 3 substrate for the analysis of real artifact objects was illustrated by the identification of alizarin extracted from a small piece of textile dyed with traditional methods and materials. The limit of detection for alizarin was estimated to be 7x10 -15 g from tests using solutions of known concentration.