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To date, detailed studies of the thickness of coatings using surface plasmon resonance have been limited to samples that are very uniform in thickness, and this technique has not been applied quantitatively to samples that are inherently rough or undergo instabilities with time. Our manuscript describes a significant improvement to surface plasmon resonance imaging (SPRi) that allows this sensitive technique to be used for quantitative tracking of the thickness and roughness of surface coatings that are rough on the scale of tens of nanometers. We tested this approach by studying samples with an idealized, one-dimensional roughness: patterned channels in a thin polymer film. We find that a novel analysis of the SPRi data collected with the plane of incidence parallel to the patterned channels allows the determination of the thickness profile of the channels in the polymer film, which is in agreement with that measured using atomic force microscopy. We have further validated our approach by performing SPRi measurements perpendicular to the patterned channels, for which the measured SPR curve agrees well with the single SPR curve calculated using the average thickness determined from the thickness profile as determined using AFM. We applied this analysis technique to track the average thickness and RMS roughness of cellulose microfibrils upon exposure to cellulolytic enzymes, providing quantitative determinations of the times of action of the enzymes that are of direct interest to the cellulosic ethanol industry.

Shell-isolated gold nanoparticles (SHINs) were employed to record shell-isolated nanoparticle-enhanced Raman spectra (SHINERS) of a passive layer formed at a gold surface during gold leaching from thiosulfate solutions. The (3-aminopropyl)triethoxysilane (APTES) and a sodium silicate solution were used to coat gold nanoparticles with a protective silica layer. This protective silica layer prevented interactions between the thiosulfate electrolyte and the gold core of the SHINs when the SHINs-modified gold electrode was immersed into the thiosulfate lixiviant. The SHINERS spectra of the passive layer, formed from thiosulfate decomposition, contained bands indicative of hydrolyzed APTES. We have demonstrated how to exploit the presence of these APTES bands as an internal standard to compensate for fluctuations of the surface enhancement of the electric field of the photon. We have also developed a procedure that allows for removal of the interfering APTES bands from the SHINERS spectra. These methodological advancements have enabled us to identify the species forming the passive layer and to determine that the formation of elemental sulfur, cyclo-S8, and polymeric sulfur chains is responsible for inhibition of gold dissolution in oxygen rich thiosulfate solutions.