We present theoretical calculations for the absorption properties of protein-coated gold nanoparticles on graphene and graphite substrates. As the substrate is far away from nanoparticles, numerical results show that the number of protein bovine serum molecules molecules aggregating on gold surfaces can be quantitatively determined for gold nanoparticles with arbitrary size by means of the Mie theory and the absorption spectra. The presence of graphitic substrate near protein-conjugated gold nanoparticles substantially enhances the red shift of the surface plasmon resonances of the nanoparticles. Our findings show that graphene and graphite provide the same absorption band when the distance between the nanoparticles and the substrate is large. However at shorter distances, the resonant wavelength peak of graphene-particle system differs from that of graphite-particle system. Furthermore, the influence of the chemical potential of graphene on the optical spectra is also investigated.
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