Sniffing Entrapped Humans with Sensor Arrays

Abstract

Earthquakes are lethal natural disasters frequently burying people alive under collapsed buildings. Tracking entrapped humans from their unique volatile chemical signature with hand-held devices would accelerate urban search and rescue (USaR) efforts. Here, a pilot study is presented with compact and orthogonal sensor arrays to detect the breath- and skin-emitted metabolic tracers acetone, ammonia, isoprene, CO2, and relative humidity (RH), all together serving as sign of life. It consists of three nanostructured metal-oxide sensors (Si-doped WO3, Si-doped MoO3, and Ti-doped ZnO), each specifically tailored at the nanoscale for highly sensitive and selective tracer detection along with commercial CO2 and humidity sensors. When tested on humans enclosed in plethysmography chambers to simulate entrapment, this sensor array rapidly detected sub-ppm acetone, ammonia, and isoprene concentrations with high accuracies (19, 21, and 3 ppb, respectively) and precision, unprecedented by portable sensors but required for USaR. These results were in good agreement (Pearson’s correlation coefficients ≥0.9) with benchtop selective reagent ionization time-of-flight mass spectrometry (SRI-TOF-MS). As a result, an inexpensive sensor array is presented that can be integrated readily into hand-held or even drone-carried detectors for first responders to rapidly screen affected terrain.

Guiding Ketogenic Diet with Breath Acetone Sensors

“…Also the high relative humidity in exhaled breath alters the sensor response to acetone [ 26 ]. To compensate for these, the Si:WO 3 sensor could be combined with other selective sensors (e.g., Ti-doped ZnO for isoprene [ 31 ], Si-doped MoO 3 for ammonia [ 32 ] and commercial humidity sensors) in orthogonal arrays [ 30 ]. 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 ).…”

“…To compensate for these, the Si:WO 3 sensor could be combined with other selective sensors (e.g., Ti-doped ZnO for isoprene [ 31 ], Si-doped MoO 3 for ammonia [ 32 ] and commercial humidity sensors) in orthogonal arrays [ 30 ]. 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.…”

“…Combined with an end-tidal breath sampler [ 28 ], such sensors have been used already to monitor fat burn rates through breath acetone online during exercise and rest in 20 volunteers in good agreement to state-of-the-art proton transfer reaction time-of-flight mass spectrometry and venous blood BOHB [ 29 ]. Even sub-ppm concentrations of breath- and skin-emitted acetone can be detected with high accuracy (i.e., 19 ppb) [ 30 ] when used in combination with isoprene-selective Ti-doped ZnO [ 31 ] and ammonia-selective Si-doped MoO 3 [ 32 ] as an orthogonal sensor array for search and rescue applications. Note that isoprene is an attractive breath marker for physical activity [ 33 ] and has potential for non-invasive cholesterol monitoring [ 34 ] while breath ammonia could be applied to detect end-stage renal disease [ 35 ].…”

Volatolomics: A broad area of experimentation

“…To assist USaR teams, researchers also developed a low-cost nanostructured metal oxide sensor array (Si-doped WO 3 , Si-doped MoO 3 , and Ti-doped ZnO) and combined it with commercial CO 2 and relative humidity sensors to detect characteristic breath and skin emitted volatile metabolic tracers (acetone -lipolysis, ammonia -protein metabolism and isoprene -biosynthesis of cholesterol) during the first 2 h of entrapment [128]. The developed sensor was tested with nine volunteers placed within a plethysmographic chamber, and its performance was evaluated with selective reagent ionization time-of-flight mass spectrometry (SRI-TOF-MS) [128]. The small size and weight alongside its high sensitivity (low ppb), specificity and response times (< 3 min) allows integration onto handheld devices of rescuers or on unmanned aerial vehicles (UAV) for remote sensing.…”

Gas sensors using ordered macroporous oxide nanostructures

“…) on sensor substrates to build a single sensor [61][62][63][64][65] and sensors arrays [66][67][68] for the selective detection of human breath biomarkers. If combined with in situ resistance measurements during deposition, the formation of highly porous networks can be monitored with morphologydependent resistance patterns to systematically design metaloxide-based gas sensors with high performances.…”