Electroless deposited silver dendrites for SERS identification of natural dyes on laboratory-dyed and historic textiles

Nanostructured silver having dendritic morphology is known to provide meaningful Raman signal enhancements. Herein, commercial silicon wafers were easily functionalized with silver dendrites by Galvanic electroless displacement. The superficial oxide layer was removed by treating the wafers with diluted HF to expose the pure silicon, which reacted with silver nitrate to form metallic silver. The morphology of the deposited silver nanostructures was assessed by SEM measurements. Afterwards, the potentialities of the fabricated substrates were tested in the analysis of several natural organic dyes used in antiquity, especially in textile dyeing, by surface-enhanced Raman scattering (SERS) spectroscopy. For the analysis, laboratory-dyed textiles were micro-extracted with a mild aqueous treatment, and the liquid fraction adsorbed and pre-concentrated on pure or functionalized silicon. The method was also applied to the analysis of dyes in archaeological Coptic textiles (30 B.C.-640 A.D.) of Egyptian origin. Together with the identification of the organic dye, the assessment of the inorganic mordant was obtained by surfaced-enhanced laser-induced breakdown spectroscopy (SENLIBS).