  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.
