Basic model for molecular sensing with molecular wires

We examine the feasibility of a molecular wire system for sensing a molecule. For a general theoretical argument on this problem, we set up a model of a short conjugated molecular wire attached on both ends to metal electrodes. The binding of a target molecule is presumed to exert an effective local perturbation in the wire. We calculate the quantum transport through the molecular wire in terms of the Green's function method. Coulomb interactions are treated in the mean field approximation with the image charge effect taken into account. The electrostatic potential and the electron charge densities on the molecular wire are determined in a self-consistent manner. It is demonstrated that the current modulation by the local perturbation grows with increasing the applied voltage, thus making the molecular sensing feasible. The magnitude of modulation depends sensitively on the position of the local perturbation, implying that a precise molecular design is necessary for optimizing the device performance.