The conduction mechanism in highly porous thick film SnO 2 sensing layers, obtained by a direct deposition technique using FSP (Flame Spray Pyrolysis), and the influence of different antimony (Sb) doping levels on the electrical properties of the host material is investigated by simultaneous DC electrical resistance and work function changes measurements in various ambient atmospheres. The situation in the case of the undoped FSP-sensors is very similar to the results obtained on polycrystalline thick film layers: we found a seamless transfer of the conduction mechanism from a depletion layer controlled one to the flat band situation and to an accumulation layer controlled one. The switch between these two models directly occurs in the absence of ambient oxygen, indicating that the depletion region is only determined by its adsorption. The degeneration of the semiconductor, in the case of the accumulation layer controlled conduction mechanism, is not observed. The addition of Sb influences the conduction mechanism dramatically due to its effect on the bulk concentration of free charge carriers. In contrast to the undoped FSP-SnO 2 sensor there is a direct switch from a conduction mechanism controlled by the depletion layer to the degenerate semiconductor situation that indicates a deep crossing of the Fermi level into the conduction band; moreover an initial upward band bending is observed.

The presence of certain volatile organic compounds (VOCs) in the breath of patients with gastric cancer has been reported by a number of research groups; however, the source of these compounds remains controversial. Comparison of VOCs emitted from gastric cancer tissue to those emitted from non-cancerous tissue would help in understanding which of the VOCs are associated with gastric cancer and provide a deeper knowledge on their generation. Gas chromatography with mass spectrometric detection (GC-MS) coupled with head-space needle trap extraction (HS-NTE) as the pre-concentration technique, was used to identify and quantify VOCs released by gastric cancer and non-cancerous tissue samples collected from 41 patients during surgery. Excluding contaminants, a total of 32 VOCs were liberated by the tissue samples. The emission of four of them (carbon disulfide, pyridine, 3-methyl-2-butanone and 2-pentanone) was significantly higher from cancer tissue, whereas three compounds (isoprene, γ-butyrolactone and dimethyl sulfide) were in greater concentration from the non-cancerous tissues (Wilcoxon signed-rank test, p < 0.05). Furthermore, the levels of three VOCs (2-methyl-1-propene, 2-propenenitrile and pyrrole) were correlated with the occurrence of H. pylori; and four compounds (acetonitrile, pyridine, toluene and 3-methylpyridine) were associated with tobacco smoking. Ex vivo analysis of VOCs emitted by human tissue samples provides a unique opportunity to identify chemical patterns associated with a cancerous state and can be considered as a complementary source of information on volatile biomarkers found in breath, blood or urine.

An innovative concept for an electronic nose (eNose) system based on a unique combination of analog and digital sensors for online monitoring is presented. The developed system consists of small sensing arrays of commercially available semiconducting metal oxide (MOX) gas sensors in a compact, modular, low sample volume, temperature-controlled sensing chamber. The sensing chamber comprises three compartments, each of which may contain several analog and/or digital MOX sensors. Additional sensors within the digital compartment allow for pressure, humidity, and temperature measurements. The presented prototype eNose system comprises one compartment with 8 analog MOX sensors and two compartments with 10 digital sensors each and was explicitly tested here for the discrimination between midrange (3–18 ppm) concentrations of ethanol and acetone at dry and moderately humid conditions.

BACKGROUND: Detection of disease by means of volatile organic compounds from breath samples using sensors is an attractive approach to fast, noninvasive and inexpensive diagnostics. However, these techniques are still limited to applications within the laboratory settings. Here, we report on the development and use of a fast, portable, and IoT-connected point-of-care device (so-called, SniffPhone) to detect and classify gastric cancer to potentially provide new qualitative solutions for cancer screening. METHODS: A validation study of patients with gastric cancer, patients with high-risk precancerous gastric lesions, and controls was conducted with 2 SniffPhone devices. Linear discriminant analysis (LDA) was used as a classifying model of the sensing signals obatined from the examined groups. For the testing step, an additional device was added. The study group included 274 patients: 94 with gastric cancer, 67 who were in the high-risk group, and 113 controls. RESULTS: The results of the test set showed a clear discrimination between patients with gastric cancer and controls using the 2-device LDA model (area under the curve, 93.8%; sensitivity, 100%; specificity, 87.5%; overall accuracy, 91.1%), and acceptable results were also achieved for patients with high-risk lesions (the corresponding values for dysplasia were 84.9%, 45.2%, 87.5%, and 65.9%, respectively). The test-phase analysis showed lower accuracies, though still clinically useful. CONCLUSION: Our results demonstrate that a portable breath sensor device could be useful in point-of-care settings. It shows a promise for detection of gastric cancer as well as for other types of disease.

Our recently demonstrated innovative concept of electronic nose (eNose) based on a combination of gas sensors was further tested and benchmarked in the present study. The system is a test...