Distribution of Silica-Coated Silver/Gold Nanostars in Soft- and Hardwood Applying SERS-Based Imaging

Nanoparticles (NPs) in aqueous suspension have just begun to be exploited for the preservative treatment of wood. However, at present, there is very little information available on the distribution of NPs in wood after impregnation, due to associated analytical challenges. In this study, we present the detection of model NPs in softwood and hardwood by surface-enhanced Raman spectroscopy (SERS). SERS is a highly sensitive analytical method requiring no fluorescent labeling. The NP distribution after impregnation is evaluated with one representative species of the two wood types. To show the feasibility of the method, we prepared SERS-active Au/Ag nanostars coated with silica to act as a model NP system. We show herein that NPs can be imaged in very low quantities in both wood types without any matrix interactions. The presence of the NPs in the wood was confirmed by scanning electron microscopy (SEM) imaging and energy dispersive X-ray analysis (EDX). The fast detection of NPs in a complex matrix, without complicated sample preparation, marks a huge step forward in the development and application of nanotechnology for wood preservation and the quest to optimize the properties of one of the world's most important raw materials.