A sensor including a surface plasmon resonance detector with a reservoir for containing a liquid sample. The sensor further includes a sensing metallic film positioned within the reservoir so that at least a majority of a surface of the sensing metallic film is to be in contact with the liquid sample being housed within the reservoir. The sensory also includes a semiconductor device having a contact in electrical communication with the sensing metal containing film that is positioned within the reservoir. The semiconductor device measures the net charges of molecules within the liquid sample within a Debye length from the sensing metallic film.