A miniaturised electrochemical sensor for detection of a component in a gas is provided. The sensor comprises a reference electrode, a counter electrode and a structure comprising a plurality of passages delineated by walls extending along the passages. A working electrode covers the walls of the structure and a layer of an ionomer covers at least part of the working electrode along the walls of the structure. The layer of ionomer is in ion conducting contact with the electrodes. The disclosure further relates to a method of fabricating a miniaturised electrochemical sensor and to a device for measuring content of NO in exhaled breath comprising such a miniaturised electrochemical sensor.