Investigation of The Nanoparticle – Support Interaction Effects of Plasmonic Gold Nanoparticles Deposited on Steel and Aluminum

Plasmonic nanoparticle (NP) based sensors have been developed to detect a wide range of analytes based on the principles of localized surface plasmon resonance (LSPR). With LSPR, the peak wavelength of absorption and scattering can shift, broaden, narrow, or be amplified or suppressed based on an interaction with the analyte of interest, allowing an optical readout. However, factors such a near-field coupling, size effects, and surface environment of the NPs can also influence the LSPR properties. Practical implementation of LSPR based sensors requires deposition of the NPs on a substrate, however most studies thus far have focused on very crystalline or pristine materials. We investigated the NP-substrate interaction effects of gold nanoparticles (AuNPs) on two industrially relevant substrates: steel and aluminum. AuNPs were drop cast on the substrates and the change in reflectivity was measured. The spectral properties were also compared to AuNPs in solution. Near field-coupling of the AuNPs was observed when the samples were transferred from water to isopropyl alcohol due to partial nanoparticle agglomeration, however this coupling effect was not observed when the particles were deposited from the isopropyl alcohol to the substrates, despite being aggregated together on the substrate. This suggests that the AuNP coupling effect to the substrate is much stronger than any NP interactions with each other. Shifts in the peak wavelengths were observed when depositing the AuNPs on the substrates, with AuNPs deposited on steel typically exhibiting a redder shift compared to AuNPs on aluminum. Variable angle measurements showed that the AuNPs absorbed strongly at low angles of incidence, with decreasing absorption as the angle increased. Other factors such as the separation of specular and diffuse reflectance, AuNP shape and size, different capping agents, and the surface roughness of the substrates were also considered. The results from this study provide valuable insight into NP – substrate interactions and will help better design LSPR based sensors for a wide range of industrial applications.