Polysaccharide-based substrate for surface-enhanced Raman spectroscopy.

Surface-enhanced Raman spectroscopy (SERS) became a useful analytical technique with the development of appropriate metallic substrates. The need for SERS substrates that immobilize metallic nanoparticles prompted this work to search for an appropriate material. This work presents the preparation, characterization and application of a SERS substrate for crystal violet (CV) detection, as the probe molecule. The inner layer of the substrate is a thin film of the fungal β-D-glucan, botryosphaeran, covered by a thin layer of silver nanoparticles (AgNPs). The nanoparticles were produced by laser ablation, a fast and clean method for their preparation, and the layers were assembled by casting. Scanning electron and atomic force microscopies, UV-VIS and Raman spectroscopy and X-ray diffraction allowed the characterization of the surface of the substrate. Analysis by Raman spectroscopy showed promising results for SERS amplification on the substrate. Detection of CV reached enhancement factors up to 106 orders of magnitude, compared to normal Raman spectra. Linearity was observed for analyses on the SERS substrate at concentration ranges of 0.005 to 1 µmol L-1. The assembly reached the detection of 12 pmol cm-2 of CV, which corresponds to 96 fg of the probe molecule contained in the area of the substrate effectively interacting with the laser. The substrate was more efficient than silver colloids to perform SERS.