(372c) Highly Selective, Flame-Made Sensors for Breath Analysis

Andreas T. Güntner and Sotiris E. Pratsinis

Particle Technology Laboratory, Institute of Process Engineering,

Department of Mechanical & Process Engineering,

ETH Zurich, CH-8092 Switzerland

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 with multi-scale process design bring this technology to synthesis of far more sophisticated materials (e.g.nanosilver, subnanoclustered catalysts & biomedical ferrofluids) and even devices¹, such as portable gas sensors for breath analysis that are the focus of this presentation.

Taking advantage of the capacity of combustion for stable synthesis of 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 type-1 tracer in the breath) at the ppb level & 90% relative humidity (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 (finger pricking) ². This led to an industrial prototype for clinical testing³ while MoO₃- and ZnO-based sensors are developed for kidney disease⁴ and cholesterol⁵monitoring, respectively.

Emphasis now is placed in development of sensor arrays (E-nose) with focus on formaldehyde (FA) as it is a potential breath marker for lung cancer and a tracer for indoor air quality monitoring⁶. Typical FA concentrations are below 100 ppb posing a sensitivity and selectivity challenge. Here, I present a highly sensitive, selective and compact electronic nose (E-nose) for on-line 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. The constituent sensors offer stable responses and detection of FA down to 5 ppb (signal-to-noise ratio > 30) at breath-realistic 90% RH. 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, NH₃and ethanol concentrations), FA is detected with an average error ≤ 9 ppb overcoming selectivity issues of single sensors. This device can 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).

5. A.T. Güntner, N. Pinau, D. Chie, F. Krumeich, S.E. Pratsinis, "Selective sensing of isoprene by Ti-doped ZnO for breath diagnostics", J. Mater. Chem. B, 4, 5358 - 5366 (2016).

6. A.T. Güntner, V. Koren, K. Chikkadi, M. Righettoni, S.E. Pratsinis, "E-nose sensing of low-ppb formaldehyde in gas mixtures at high relative humidity for breath screening of lung cancer?", ACS Sensors, 1, 528-535 (2016).