Enhancing Surface Plasmon Resonance Detection Using Nanostructured Au Chips

The increase of the sensitivity of surface plasmon resonance (SPR) refractometers was studied experimentally by forming a periodic relief in the form of a grating with submicron period on the surface of the Au-coated chip. Periodic reliefs of different depths and spatial frequency were formed on the Au film surface using interference lithography and vacuum chalcogenide photoresists. Spatial frequencies of the grating were selected close to the conditions of Bragg reflection of plasmons for the working wavelength of the SPR refractometer and the used environment (solution of glycerol in water). It was found that the degree of refractometer sensitivity enhancement and the value of the interval of environment refractive index variation, Δn, in which this enhancement is observed, depend on the depth of the grating relief. By increasing the depth of relief from 13.5 ± 2 nm to 21.0 ± 2 nm, Δn decreased from 0.009 to 0.0031, whereas sensitivity increased from 110 deg./RIU (refractive index unit) for a standard chip up to 264 and 484 deg./RIU for the nanostructured chips, respectively. Finally, it was shown that the working range of the sensor can be adjusted to the refractive index of the studied environment by changing the spatial frequency of the grating, by modification of the chip surface or by rotation of the chip.