  We discuss the renormalization of the polarizability of a nanoparticle in the
presence of either (i) a continuous graphene sheet or (ii) a plasmonic graphene
grating, taking into account retardation effects. Our analysis demonstrates
that the excitation of surface plasmon-polaritons in graphene produces a large
enhancement of the real and imaginary parts of the renormalized polarizability.
We show that the imaginary part can be changed by a factor of up to 100
relatively to its value in the absence of graphene. We also show that the
resonance in the case of the grating is narrower than in the continuous sheet.
In the case of the grating it is shown that the resonance can be tuned by
changing the grating geometric parameters.
