A coated-wire potentiometric sensor comprising an electronically conducting substrate electrode coated with an ionically conductive sensing layer and an outermost surface consisting of or comprising in and/or on a first molecular species which is capable of reversibly adsorbing a second molecular species and a method for measuring the affinity between a first molecular species and a second molecular species comprising the steps of: providing a potentiometric sensor of the coated-wire type having an outermost surface; adapting said outermost surface so that consists of or comprises said first molecular species; placing said sensor in a system for the recording of sensorgrams; recording a sensorgram of the adsorption of a second molecular species on said first molecular species of or comprised in and/or on said adapted outermost surface.