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. Our results show that the conductivity can be expressed in terms of renormalized quasiparticle parameters (nu) over tilde (F), (M) over tilde, and (mu) over tilde that include the effect of the molecular surface concentration n(dip) and dipolar moment P, thus providing a quantum field theory approach to model a graphene-based chemical sensor.