  We studied theoretically the effect of a low concentration of adsorbed polar
molecules on the optical conductivity of graphene, within the Kubo linear
response approximation. Our analysis is based on a continuum model
approximation that includes up to next to nearest neighbors in the pristine
graphene effective Hamiltonian, thus extending the field-theoretical analysis
developed in Refs.[1,2]. Our results show that the conductivity can be
expressed in terms of renormalized quasiparticle parameters $\tilde{v}_F$,
$\tilde{M}$ and $\tilde{\mu}$ that include the effect of the molecular surface
concentration $n_{dip}$ and dipolar moment $\boldsymbol{\mathcal{P}}$, thus
providing an analytical model for a graphene-based chemical sensor.
