Highly selective, flame-made nanostructured sensors for breath analysis

S.E. Pratsinis
ETH Zurich,
Switzerland

Keywords: sensor, nanoparticle synthesis

Summary:

Flame aerosol technology dominates the manufacture of nanostructured materials at tons/h, albeit rather simple ones (carbon blacks, fumed silica, alumina, titania etc.). Recent advances in combustion and aerosol science, including cluster dynamics, extend now the use of this undisputably scalable technology to synthesis of far more sophisticated materials and even devices focusing on portable gas sensors for breath analysis1. So capitalizing on the capacity of combustion to capture stably nanostructured metastable phases and solid solutions, flame aerosol deposition and in-situ annealing of gas sensor films is presented as it had led, first, to optimally-doped SnO2 for ethanol and CO sensing and, most notably to epsilon-WO3 for selective detection of acetone (a diabetes tracer in the breath) at the ppb level & 90% RH. In tandem with PTR-MS, such a portable breath sensor was used for online and offline testing of humans benchmarked with standard glucose tests on humans (finger pricking) 2. Last year a prototype was assembled by industry for clinical testing3 while new MoO3 –based sensors are developed for kidney disease monitoring4. Emphasis now is placed in development of an E-nose with focus on formaldehyde (FA) as it is a potential breath marker for lung cancer and a tracer for indoor air quality monitoring. Typical FA concentrations are below 100 ppb posing a sensitivity and selectivity challenge to current portable sensor systems. Here, I present a highly sensitive, selective and compact electronic nose (E-nose) for real-time quantification of FA in realistic gas mixtures. This E-nose consists of four nanostructured and highly porous Pt-, Si-, Pd- and Ti-doped SnO2 sensing films directly deposited onto silicon wafer-based microsubstrates by flame spray pyrolysis (FSP). The constituent sensors offer stable responses and detection of FA down to 5 ppb (signal-to-noise ratio > 30) at breath-realistic 90% relative humidity. Each dopant induces different analyte selectivity enabling selective detection of FA in gas mixtures by multivariate linear regression. In simulated breath (FA with higher acetone, NH3 and ethanol concentrations), FA is detected with an average error ≤ 9 ppb using the present E-nose and overcoming selectivity issues of single sensors. This device could facilitate easy screening of lung cancer patients and monitoring of indoor FA concentrations. . 1. Aerosol-based Technologies in Nanoscale Manufacturing: from Functional Materials to Devices through Core Chemical Engineering, AIChE J., 56, 3028-3035 (2010). 2. M. Righettoni, A. Schmidt, A. Amman, S.E. Pratsinis, “Correlations between blood glucose & breath components from portable gas sensors and PTR-TOF-MS”, J. Breath Res., 7, 037110 (2013). 3. M. Righettoni, A. Ragnoni, A.T. Güntner, C. Loccioni, S.E. Pratsinis, T.H. Risby, "Monitoring breath markers under controlled conditions", J Breath Res., 9, 047101 (2015). 4. A.T. Güntner, M. Righettoni, S.E. Pratsinis, "Selective sensing of NH3 by Si-doped α-MoO3 for breath analysis", Sensors and Actuators B: Chemical, 223, 266–273 (2016).