The present invention provides a sensor including an acidic medium; a first electrode disposed in the acidic medium; a basic medium adjacent to or close to the acidic medium; a second electrode disposed in the basic medium; and a detector for detecting one of voltage and current that is generated between the first and second electrodes by a first substance which causes a reaction of removing electrons from the first electrode with hydrogen ions contained in the acidic medium, and a second substance which causes a reaction of supplying electrons to the second electrode with hydroxide ions contained in the basic medium, and provides a method of detecting a substance using the sensor.