Selective sensing of NH 3 by Si-doped α-MoO 3 for breath analysis

Ammonia is an important breath marker for non-invasive detection and monitoring of end-stage renal disease (ESRD). Here, a chemo-resistive gas sensor has been developed consisting of flame-made nanostructured α-MoO3, a promising phase for selective detection of breath NH3. A key novelty is the thermal stabilization of α-MoO3 by Si-doping inhibiting sintering and crystal growth at the operational conditions of such sensors. Therefore, pure and Si-doped MoOx nanoparticles were made by flame spray pyrolysis (FSP) and directly deposited onto sensor substrates forming highly porous films with ribbon-like and nanoparticle/needle-like morphologies, respectively. In situ XRD analysis of the MoOx phase dynamics revealed a thermally induced recrystallization of β-MoO3 at 300–350 °C and optimal annealing at 450 °C for synthesis of highly nanocrystalline α-MoO3. For selective NH3 sensing, however, the optimum SiO2 content was 3 wt% and the operational temperature 400 °C. This sensor showed superior NH3 selectivity toward acetone, NO and CO, and accurately detected breath-relevant NH3 concentrations down to 400 ppb under 90% relative humidity (RH). As a result, a stable and inexpensive sensor for NH3 is presented which has the potential for further development toward a hand-held device for the early-stage diagnosis and monitoring of ESRD.