Oxide Surface Plasmon Resonance for a New Sensing Platform in the Near‐Infrared Range

A new sensor platform is realized by surface plasmon resonance on doped oxide semiconductors of In₂O₃:Sn layers (oxide‐based SPR) in the near‐infrared range. The detection sensitivity of oxide‐based SPR is initially demonstrated by enhancement of the absorption band ascribed to molecular‐vibrational modes in the NIR range, which indicates that the enhancing effects occur only when coupling is achieved between excitations of surface plasmons and molecular vibrations. These results are supported by theoretical analyses of electromagnetic field amplitudes on the layer surfaces. Further studies with SPR measurements of glucose‐water solutions reveal that the precise detection sensitivity (S) of oxide‐based SPR is 7576 nm RIU⁻¹, which is consistent with the theoretically estimated sensitivity (S = 7447 nm RIU⁻¹). The experimentally and theoretically obtained resolution in the refractive index is on the order of 10⁻⁵, which also supports the appearance of molecular‐vibrational modes in the SPR spectra. Finally, it is found that the detection sensitivity of oxide‐based SPR is close to that of Au metal‐based SPR working in the visible range, a result that is discussed in relation to the spatial coherence and major characteristics of SP waves at the metal–water interfaces of In₂O₃:Sn and Au layers.