E-Nose Sensing of Low-ppb Formaldehyde in Gas Mixtures at High Relative Humidity for Breath Screening of Lung Cancer?

Formaldehyde (FA) is a potential breath marker for lung cancer and a tracer for indoor air quality monitoring. Its typical concentrations are below 100 ppb posing a sensitivity and selectivity challenge to current portable sensor systems. Here, we present a highly sensitive, selective, and compact electronic nose (E-nose) for real-time quantification of FA at realistic conditions. 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 (24 h tested) and detection of FA down to 3 ppb (signal-to-noise ratio > 25) at breath-realistic 90% relative humidity. Each dopant induces different analyte selectivity enabling selective detection of FA in two-, three- and four-analyte 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.