Self-referenced plasmonic biosensor with gold grating on thin gold film

Surface plasmon resonance sensors based on grating coupling exhibiting two resonant wavelengths are less observed because usually thick metal films are used. In this paper, we propose gold gratings on a gold film with two narrow reflection dips. One is sensitive to the refractive index (RI) of the cover media with a sensitivity of 720 nm/RIU. However, the other is sensitive to the RI of the substrate, and hence, it can be used as a reference dip. This self-referenced sensor significantly reduces the error contributions of the light intensity fluctuations and temperature variation. Moreover, the electric field is stronger with less decay length than that of gold gratings without gold film. Therefore, gold gratings with a gold film are more suitable to be a biosensor. Besides, we also investigate the structure parameters (the thickness of the gold film, the thickness and width of gold gratings, and the RI of the substrate) on the reflection spectra.