Single-layer graphene-based surface plasmon resonance biosensors for immunization study

In this study, we have developed a kind of single-layer graphene-based surface plasmon resonance (SLG-SPR) biosensor with wavelength interrogation to detect C-reactive protein (CRP) by sandwich immunoassay. For the nature of the biosensor itself, with the decrease of the incidence angle (θ), resonance wavelength (λ_R) increased gradually. The refractive index sensitivity (S) and θ are inversely proportional relationship while S and λ_R are positively proportional relationship. Then we studied two kinds of sensitivity properties of these two SPR biosensors respectively. The refractive index (RI) sensitivity of the two biosensors is approximately the same and the high sensitivity of SLG-SPR biosensor due to the excellent adsorption properties of graphene. The experiment shows that the changes in resonance wavelength (▵λR) of SLG-SPR biosensor are higher than that of the gold film based SPR (Au-SPR) biosensor when the final sandwich structures were formed. Meanwhile, we have applied the Fresnel reflection equations and Bruggeman approximation formula to calculate the volume fractions of adsorbates in different adlayers, and the dispersion curves of the effective RI of adsorbates with different volume fractions of adlayers and the cAb isothermal adsorption curves that conforms to Langmuir equation were obtained. In conclusion, the SLG-SPR biosensor with a higher detection sensitivity than the conventional Au-SPR biosensor in detecting CRP and it has the advantages of low-cost, stability, highly efficient for the clinical determination of CRP levels.