Sensitive ‘on the fiber’ detection of synthetic organic dyes by laser photoinduced plasmonic Ag nanoparticles

The photoreduction of aqueous Ag+ to silver nanoparticles (AgNPs) on a substrate was studied aiming at the application of surface-enhanced Raman scattering (SERS) technique to the sensitive analysis of organic colorants directly on artworks. In particular, the presence of the synthetic dyes methyl violet (BV1) and fuchsine (BV14), in both standard and historical wool fibers, was analyzed. Scanning electron microscopy was employed to study the morphology and distribution of the NPs obtained on the fiber. We have carried out an investigation of the influence of several factors on the morphology of NPs: excitation wavelength, substrate, laser power and laser irradiation time. The resulting materials were analyzed at different laser wavelengths in order to evaluate the application range of the probe laser after the NPs formation. SERS spectra of the BV1 and BV14 dyes on the fiber were obtained and compared with those obtained in suspended conventional AgNPs, in order to deduce the possible influence of the wool substrate on the Raman spectra. SERS spectra were analyzed considering the possible resonance Raman processes. Bands attributed to the protein substrate were also identified. The main goal of this work was to assess and optimize a general method of analysis of organic dyes on natural fibers based on the direct preparation of AgNPs by laser SERS technique. Copyright © 2017 John Wiley & Sons, Ltd.