Highly Selective and Rapid Breath Isoprene Sensing Enabled by Activated Alumina Filter

Abstract

Isoprene is a versatile breath marker for noninvasive monitoring of high blood cholesterol levels as well as for influenza, end-stage renal disease, muscle activity, lung cancer, and liver disease with advanced fibrosis. Its selective detection in complex human breath by portable devices (e.g., metal-oxide gas sensors), however, is still challenging. Here, we present a new filter concept based on activated alumina powder enabling fast and highly selective detection of isoprene at the ppb level and high humidity. The filter contains high surface area adsorbents that retain hydrophilic compounds (e.g., ketones, alcohols, ammonia) representing major interferants in breath while hydrophobic isoprene is not affected. As a proof-of-concept, filters of commercial activated alumina powder are combined with highly sensitive but rather nonspecific, nanostructured Pt-doped SnO sensors. This results in fast (10 s) measurement of isoprene down to 5 ppb at 90% relative humidity with outstanding selectivity (>100) to breath-relevant acetone, ammonia, ethanol, and methanol, superior to state-of-the-art isoprene sensors. Most importantly, when exposed continuously to simulated breath mixtures (four analytes) for 8 days, this filter-sensor system showed stable performance. It can be incorporated readily into a portable breath isoprene analyzer promising for simple-in-use monitoring of blood cholesterol or other patho/physiological conditions.

Guiding Ketogenic Diet with Breath Acetone Sensors

“…Such improved accuracy is especially required when lower ppb concentrations of acetone need to be detected (e.g., in search and rescue when sniffing entrapped humans [ 30 ]) but less important in KD monitoring where exhaled acetone concentrations are at elevated ppm levels ( Figure 2 ). Also filters (e.g., microporous membranes [ 51 ] for larger interfering molecules or adsorption packed beds [ 52 ]) or GC columns [ 53 ] are quite effective to improve selectivity.…”

Rapid and Selective NH3 Sensing by Porous CuBr

“…Also ethanol (selectivity ≈40) may be present at high ppm concentrations in the background of hospital air from disinfectants or cleaning agents. [34] However, this can be improved by combining the CuBr sensor with microporous membranes [35] or sorption columns (e.g., packed beds of activated ceramics [36] or polymers [37] ) that can remove critical confounders.…”

Sniffing Entrapped Humans with Sensor Arrays

“…2 ( Figure 3 b, triangles), ammonia levels increase steadily, consistent with slower rising RH levels ( Figure 3 d) that might be associated with his skinny physique (lowest weight at normal height, Table S2 ). Note that tracer concentrations may be altered also by construction materials, such as alumina that retains hydrophilic molecules, 32 or other background effects (e.g., fire or garbage) possibly present in USaR environments. Nevertheless, ammonia is still a promising human tracer due to its high skin emission rate and thus rapid accumulation in the vicinity of a person.…”