Ag‐Cu Nanoarchitecture for Enhanced LSPR Absorption: the Role of Surface Roughness and near‐field Interactions

Abstract The plasmonic properties and biosensing performance of a nanocomposite with incorporated Cu and Ag nanoparticles (NPs) are studied experimentally. The concept's viability is verified by detecting specific anti‐decorin‐binding protein A (DbpA) from Borrelia afzelii antibodies, typically produced by a living organism in response to Lyme disease infection, carried out in real‐life negative and positive blood sera. It is shown that the addition of Cu NPs on top of silver NPs regularly boosts the plasmonic absorption caused by optical and electrical changes in the vicinity of the surface compared to silver NPs only. The Finite‐difference time‐domain (FDTD) simulations of near‐field interaction in different environments propose suitable Cu–Ag coupling modes responsible for the modulation of the localized Surface Plasmon Resonance (LSPR) bands. Furthermore, the increased surface roughness, resulting from the architecture of combined nanoparticles of different metals, significantly enlarges the effective surface area for sensing applications, which consequentially leads to better species immobilization. The observed distinguishable differences between the negative and positive sera of LSPR response, and the high sensitivity and selectivity together with high stability of the nanocomposite (suppressed aging) opens a door for concepts of rapid, low‐cost, sensitive LPSR‐based biodetection platforms.