This paper presents development of real time monitoring of binding events on flexible plastic in microchips. Two planar carbon microelectrodes are integrated into an insulated polyethylene terephthalate microchip without direct electrical contact with the solution in the microchannel. It has been possible to probe the electric impedance changes through the interface constituted by the microelectrode/PET microchannel/solution when a biomolecular interaction takes place on the polymer surface. This new transduction for biosensing was demonstrated for the molecular recognition of BSA immobilized on the polymer microchannel surface using the corresponding rabbit anti-BSA antibodies as an analyte in the flow microchannel at the nanomolar range concentration. The equilibrium association constant was determined for the affinity reaction between both ligands and was obtained equal to 5 × 10(7) M(-1). The promising results obtained with this new device make it a competitive biosensor.