An optical biosensor based on localized surface plasmon resonance of silver nanostructured films

Ag nanostructured films fabricated by the reduction of sputtered AgOx thin films are shown to exhibit a strong localized surface plasmon resonance (LSPR) at wavelengths around 370 nm. The spectral position of the LSPR, defined as the wavelength of minimal reflectance, shifts linearly depending on the refractive index n of the surrounding medium in a range of n = 1.0–1.5. By the immobilization of biotin molecules at the Ag surface, events of binding between the immobilized biotin and solution-phase streptavidin were probed for streptavidin concentrations in a range of 16 nM–8 µM. From the sigmoidal fitting of the data, the surface-confined binding affinity constant was estimated as Ka,surf = 3.0 × 106 M−1. These results experimentally demonstrate the great potential of the Ag nanostructured films for application as cost-effective LSPR biosensors.