A device and method which comprises a sensing surface on a membrane, solid surface or electrode, where the sensing surface contains a photo-voltage active material chosen in relation to a particular target substance to be detected and quantified. The photo-voltage active material is of a type which produces an interfacial photo-voltage electrical signal upon illumination. The particular photo-voltage active material chosen for a particular target substance is one in which the presence of the target substance causes a change in the electrical signal produced. The presence of the target substance modifies the expected photo-voltage produced by the sensing surface upon illumination. The photo-voltage produces signals which are detected by electronic circuits, and the presence and concentration of the target substance is determined by analyzing the difference between the photo-voltage of the target sample versus the photo-voltage of a control sample lacking the target substance.