Investigation of the Nanoparticle-Support Interaction Effects of Plasmonic Gold Nanoparticles Deposited on Nonpristine Aluminum and Steel Substrates.

Plasmonic nanoparticle (NP) sensors have been proposed to detect many analytes based on the principles of localized surface plasmon resonance (LSPR). They depend on spectral changes like peak wavelength, intensity, or broadness upon interaction with the analyte of interest, allowing optical readouts. However, they are also sensitive to factors like near-field coupling, size effects, and surface environment. For many applications, practical implementation of LSPR based sensors requires deposition of the NPs on a substrate. However, most studies to date have focused on highly crystalline or pristine materials which are impractical for scaled up industrial applications due to cost and size limitations. In this work, we investigate the NP-substrate interaction effects of gold NPs (AuNPs) deposited on two industrially relevant substrates: aluminum and steel. The AuNPs were dropcast on the substrates and the change in reflectivity before and after AuNP deposition was measured. Near-field coupling of the AuNPs was minimal after deposition on the substrates despite being observed on the AuNPs in solution. The spectral peak positions of the AuNPs were influenced by both the substrate and the surface environment. Variable angle measurements showed strong AuNP absorbance at low angles of incidence, with decreasing absorption as the angle increased. Larger particles had higher diffuse components while smaller particles favored specular reflection. Surface roughness showed limited influence on the overall observed intensities. From these observations, we outline a set of guidelines for solid supported plasmonic NP based sensors to optimize signal intensity and accuracy of measurement.