Sensitivity analysis of a nanowire-based surface plasmon resonance biosensor in the presence of surface roughness

We have investigated the effect of surface roughness on the sensitivity of conventional and nanowire-based surface plasmon resonance (SPR) biosensors. The theoretical research was conducted using rigorous coupled wave analysis with Gaussian surface profiles of gold films determined by atomic force microscopy. The results suggest that, when surface roughness ranges near 1 nm, the sensitivity of a conventional SPR system is not significantly affected regardless of the correlation length. For a nanowire-based SPR biosensor, however, we have found that the sensitivity degrades substantially with decreasing correlation length. In particular, at a correlation length smaller than 100 nm, a random rough surface may induce destructive coupling between excited localized surface plasmons, which can lead to prominent reduction of sensitivity enhancement.