The sensing element of the sensor is covered with a series of gas permeable membranes allowing only certain types of gas to pass through.NO diffuses through these membranes and reacts at the electrode surface.The exchange of electrons between NO and the electrode surface results in an electrical current that is monitored and recorded.The magnitude of the electrical current is directly proportional to the amount of NO diffused through the membranes, which is proportional to the concentration of NO in the sample.