#$%^&*AU2014200951A120140313.pdf#####ABSTRACT A sensor for sensing a target substance in a gas stream is provided, the sensor comprising: a sensing element disposed to be exposed to the gas stream, the sensing element comprising: a working electrode a counter electrode and a layer of ion exchange material extending between the working electrode and the counter electrode whereby contact of the ion exchange layer with the gas stream forms an electrical contact between the working and counter electrodes.
