Near-IR surface-enhanced Raman spectrum of lignin

Compacted powders of commercially available nano- and microparticles of silver were used to successfully induce the surface-enhanced Raman scattering (SERS) effect in spruce milled-wood lignin (MWL). For the two silver particle sizes used in this investigation, the spectra were mostly similar. Some general characteristics of the lignin SERS spectrum are described. The SERS technique was found to be sensitive for detecting lignin. Significant spectral changes were present between the SERS and normal Raman spectra of MWL. The SERS spectrum was assigned on the basis of literature-reported vibrational assignments of lignin and its models. Based on significant changes in Raman features, we propose that the lignin is strongly adsorbed on silver. To determine whether SERS of lignin can be obtained directly from wood without its isolation, Wiley-milled spruce wood (WMW) adsorbed on silver was studied. The results indicated that not only the surface-enhancement effect was successfully induced in the WMW, but that its spectrum was similar to MWL SERS. Moreover, for WMW, no signals from the carbohydrate components were observed, and therefore, lignin was detected selectively. This nano-and microparticle-based molecularly specific method is expected to make a significant contribution in identifying and investigating lignin in various lignin-containing materials. Published in (C) 2009 by John Wiley & Sons, Ltd.