GRAPHENE EFFECT IN SURFACE PLASMON RESONANCE OPTICAL SENSORS

The surface plasmon resonance SPR technique reveals for a metal-dielectric interface, where p-polarized incident light beams interact with superficial longitudinal oscillations (surface plasmons) on the metal layer. The... [ view full abstract ]

The surface plasmon resonance SPR technique reveals for a metal-dielectric interface, where p-polarized incident light beams interact with superficial longitudinal oscillations (surface plasmons) on the metal layer. The Krestchmann configuration, proposed in 1968, uses the Attenuated Total Reflection (ATR) method and basically consists of three layers: an optical substrate, a metallic thin film and a dielectric (interest substance for sensing). SPR sensors that use optical fibers as photon-plasmon coupling elements have been evidenced in the last decades due to advantageous characteristics, like: possibility of miniaturization, remote access, immunity to electromagnetic interference, flexibility, among other features. Varying some construction parameters of an optical fiber, like the fiber diameter, the thickness of the sensing region and the length of the sensing region, the sensitivity increases. Another possibility is the use of Graphene to reinforce the evanescent electric field on the metal-dielectric interface and consequently leads to a higher sensitivity or even another figure of merit, like detectivity. This is due to its high electrical conductivity, which facilitates the transport and interaction of the metal charge region with the biomolecules. Here, the investigation of the influence of graphene layers arranged on a thin gold film is performed for SPR sensors using the polymeric optic fiber. The incident light transmittivity increased for a 700 nm laser (angular interrogation mode). Adding graphene layers between the metal thin film and the dielectric layer (analyte), a shift in the resonance point has been observed with a corresponding increase in the reflectance (Figure 1).
Figure 1. SPR curve for different quantities of graphene layers.