Sulfur‐Doped Nanostructured Copper Iodide Films for Chemiresistive Ammonia Sensors Analyzing Exhaled Breath

Chemiresistive room‐temperature sensors based on sulfur‐doped copper iodide films have been developed and tested, which are suitable for the selective detection of ammonia (NH₃) in exhaled air for the purpose of disease diagnosis and monitoring. The films are deposited on glass and flexible polyethylene substrates and have a morphology of nanoflakes or triangular nanograins containing from 2 to 8 at% S depending on the mode of the automatic successive ionic layer adsorption and reaction method. The interfering effect of water vapor, acetone, and ethanol on the response of the ammonia sensors is insignificant due to the specific chemical interaction of copper iodide with ammonia. The high conductivity of the films allows the sensors to produce significant signals above noise‐limited detection levels even at sub‐ppm NH₃ concentrations. The detection limit of the developed sensors ≈0.15 ppm NH₃ is two times lower than the typical level of ammonia in the exhaled breath of a healthy person. The ammonia responses and response/recovery times are among the best chemiresistive sensors operating at room temperature. Using a low 1 V bias voltage for room temperature operation allows the sensors to be integrated with smartphones, giving them autonomy.