The present disclosure provides embodiments for diodes, devices, and methods for polar vapor sensing. One embodiment of a diode includes a first electrode to which an electric field is applied; a second electrode to which the electric field is applied; and a vapor gap region between the first electrode and the second electrode. A total capacitance measured between the first electrode and the second electrode varies based on presence of a polar vapor species on at least a portion of an electrode surface of at least one of the first electrode and the second electrode.