Abrupt phase change in graphene-gold spr-based biosensor

The performance of surface plasmon resonance (SPR) sensors can be different depending on which characteristic of the SPR sensor the amplitude or the phase is monitored. The phase sensitivity strongly depends on the geometry and the optical properties of the system. The existence of sharp changes in the phase spectrum variations is found as the thickness of SPR-supporting gold ( d g ) varies around a critical thickness ( d c ). In addition, the simulation results indicate that the phase sensitivity is divided into two regions so that phase sensitivity S φ for region d g ≤ d c is greater than region d g  >  d c . It is demonstrated in condition of d g ≤ d c the phase sensitivity has a strong jump when the sensing medium refractive index lies within a certain interval, while the amplitude sensitivity has a monotonic shape. The phase analysis from another aspect exhibits that the phase maximum difference Δ φ max towards the blank sample is sensitive to refractive index in a continuous interval. As a result, the phase detection interval is tunable by varying the gold thickness, which potentially is important for medical, biology and chemistry applications.