We report the high performance of Au-coated SnO2 nanorod gas sensors for the detection of hazardous indoor volatile organic compounds (VOCs), such as benzene, toluene, xylene, and formaldehyde (BTXF) ...gases. Densely ordered SnO2 nanorod arrays were prepared via glancing angle deposition with an electron beam evaporator. The Au layer coating was used as a heterogeneous catalyst to promote the oxidation of VOCs, such as hydrocarbons. After optimizing the Au thickness, the sensor exhibited an excellent sensing response and a rapid response time of < 2.5 s for 10 ppm of BTXF gases. The maximum response was ∼662 for formaldehyde at 400 °C, ∼328 for toluene at 450 °C, ∼170 for xylene at 400 °C, and ∼139 for benzene at 500 °C, which are significantly higher than those of previously reported metal-oxide-semiconductor-based sensors. Each gas was selectively detected by integrating the sensor into a miniaturized gas chromatography (GC) system. The sensors detected ppb-level gas concentrations. Significantly, GC analysis revealed that four types of gases could be separately detected in a mixed gas within 5 min. Our study shows that Au-coated SnO2 nanorod gas sensors integrated with GC can be used as a facile indoor pollutant monitoring system.
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•We present the high-performance Au-coated SnO2 nanorod sensor for real-time indoor air pollutant monitoring.•The sensor exhibited an excellent sensing performance for benzene, toluene, xylene, and formaldehyde.•Each gas was able to detect at ppb-level by integrating the sensor into a miniaturized gas-chromatography (GC) system.•Significantly, four types of gases could be separately detected in a mixed gas within 5 min.
We report a breath hydrogen analyzer based on Pd-coated SnO2 nanorods (Pd-SnO2 NRs) sensor integrated into a miniaturized gas chromatography (GC) column. The device can measure a wide range of ...hydrogen (1–100 ppm), within 100 s, using a small volume of human breath (1 mL) without pre-concentration. Especially, the mini-GC integrated with Pd-SnO2 NRs can detect 1 ppm of H2, as a lower detection limit, at a low operating temperature of 152 °C. Furthermore, when the breath hydrogen analyzer was exposed to a mixture of interfering gases, such as carbon dioxide, nitrogen, methane, and acetone, it was found to be capable of selectively detecting only H2. We found that the Pd-SnO2 NRs were superior to other semiconducting metal oxides that lack selectivity in H2 detection. Our study reveals that the Pd-SnO2 NRs integrated into the mini-GC device can be utilized in breath hydrogen analyzers to rapidly and accurately detect hydrogen due to its high selectivity and sensitivity.
•We developed a new acetylene analyzer for transformer oils.•A sensor based on Pd-coated SnO2 nanorods was utilized in a miniaturized gas chromatography.•The performance of sensors was considerably ...enhanced by coating SnO2 nanorods with Pd.•The device performed well in sensitive and selective detection in a short time.
We report on the sensitive and selective sensing properties of SnO2 nanorods (NRs) based gas sensors coupled with a miniature gas chromatography (mini-GC) system for the detection of acetylene. The SnO2 NRs were fabricated by a glancing angle deposition (GLAD) method and their average height and diameter were ∼200 nm and ∼30 nm, respectively. In order to overcome a selectivity issue of metal oxide semiconductor gas sensors, we integrated our SnO2 NRs based sensors with a packed column. The device accurately and selectively detected acetylene within 2 min (∼120 s). We found that loading a thin layer (5 nm) of metal catalysts such as Au, Pt or Pd increases the sensing abilities of the SnO2 NRs sensors. Among the tested sensors, the Pd-coated SnO2 NRs sensor (Pd-SnO2 NRs) exhibited the best sensing performance for the detection of 10 ppm of acetylene and the lower detection limit of 0.01 ppm. The superior sensing properties of Pd-SnO2 NRs are due to the large amount of oxygen deficiencies on the surface of Pd-SnO2 NRs, which acts as reactive sites. More importantly, the mini-GC device can be used to selectively detect 10 ppm of acetylene from other gases such as H2. Our findings demonstrate that Pd-SnO2 NRs integrated with a mini-GC device can be utilized to monitor the dissolved acetylene gas in transformer oil in real time.
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•We report on a breath-isoprene analyzer based on a gas chromatography column with catalyst-coated In2O3 thin films.•We found that Pd-coated In2O3 thin films were superior to Au- and ...Pt-coated films.•The analyzer was able to selectively detect isoprene in air within 2 min at 196 °C.•The detection limit was 0.4 ppb, which is the lowest level reported to date.•Our study demonstrates that the analyzer can be utilized to rapidly and accurately detect isoprene in breath.
Monitoring breath isoprene concentration plays a role in non-invasive diagnosis of blood-cholesterol levels. In this study, we developed a highly sensitive and selective isoprene analyzer based on a Pd-coated In2O3 thin film integrated in a miniaturized gas chromatography column. To improve the sensing performance, the In2O3 thin films were fabricated with high uniformity and crystallinity using a dual-ion-beam sputtering system, and various metal catalysts (Au, Pt, and Pd) were loaded on the film surface. Among them, the Pd catalyst afforded the highest sensing reaction and the lowest detection limit (approximately 0.4 ppb), which is the best performance ever reported. It also significantly lowered the optimal operating temperature of the sensor from 432 °C to 196 °C. The excellent isoprene sensing performance of the Pd-coated In2O3 film can be attributed to the high density of oxygen vacancies, efficient reduction-reoxidation of PdO, and the Mars-van-Krevelen catalytic reaction. We further optimized the isoprene sensing performance of a Pd-coated In2O3 film by varying the Pd thickness and discovered that 1 nm of Pd deposition showed the optimal status of discontinuous islands for sensing. We expect that our device can be applied to a portable breath isoprene analyzer.
•We developed a new chemical warfare agent simulant analyzer for 2-CEES detection.•A sensor based on Al-doped ZnO quantum dots was adopted in a miniaturized GC.•The detection time of 2-CEES was ...considerably reduced by optimizing column length.•The device performed well in sensitive and selective detection in a short time.
We report a new portable chemical warfare agent analyzer for miniaturized gas chromatography (mini-GC), comprising a packed column and hydrothermally synthesized Al-doped ZnO quantum dots (AZO QDs). This device uses a small volume of the target gas (1 ml) without pre-concentration and can be used to detect 2-chloroethyl ethyl sulfide (2-CEES) gas, which is a mustard gas simulant, over a wide concentration range. The AZO QD (˜5 nm) sensor exhibited an outstanding sensing response (R) of 5,393 in detecting 20 ppm of 2-CEES; this performance is superior to those of other previously reported 2-CEES sensors based on semiconducting metal oxides. By optimizing the length of the packed column, we successfully decreased the retention time of 2-CEES to ˜150 s. More importantly, the manufactured mini-GC device can be used to selectively detect a small amount of target gas from other gases such as NH3, NO, and CO. We demonstrated the excellent detection performance of the device for the real-time selective detection of 2-CEES.
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•Successful synthesis of Co-doped ZnO spherical bead through a sonochemical process.•Optimal sensor operating temperature reduction down to 250 °C due to Co doping.•Fabrication of ...sensors with a response 7.9 to 1 ppm acetone gas.•Fabrication of sensors with the lowest acetone detection concentration of 43 ppb.•Successful measurement of acetone concentration (0.44 ppm) from 1 ml real exhalation.
In this study, we introduce cobalt (Co)-doped zinc oxide (ZnO) spherical beads (SBs), synthesized using a sonochemical process, and their utilization for an acetone sensor that can be applied to an exhalation diagnostic device. The sonochemically synthezied Co-doped ZnO SBs were polycrystalline phases with sizes of several hundred nanometers formed by the aggregation of ZnO nanocrystals. As the Co doping concentration increased, the amount of substitutionally doped Co2+ in the ZnO nanocrystals increased, and we observed that the fraction of Co3+ in the Co-doped ZnO SBs increased while the fraction of oxygen vacancies decreased. At an optimal Co-doping concentration of 2 wt%, the sensor operating temperature decreased from 300 to 250 °C, response to 1 ppm acetone improved from 3.3 to 7.9, and minimum acetone detection concentration was measured at 43 ppb (response, 1.75). These enhancements are attributed to the catalytic role of Co3+ in acetone oxidation. Finally, a sensor fabricated using 2 wt% Co-doped ZnO SBs was installed in a commercially available exhalation diagnostic device to successfully measure the concentration of acetone in 1 ml of exhaled air from a healthy adult, returning a value of 0.44 ppm.
When attempts to lose body fat mass frequently fail, breath acetone (BA) monitoring may assist fat mass loss during a low-carbohydrate diet as it can provide real-time body fat oxidation levels. This ...randomized controlled study aimed to evaluate the effectiveness of monitoring BA levels and providing feedback on fat oxidation during a three-week low-carbohydrate diet intervention. Forty-seven participants (mean age = 27.8 ± 4.4 years, 53.3% females, body mass index = 24.1 ± 3.4 kg m
) were randomly assigned to three groups (1:1:1 ratio): daily BA assessment with a low-carbohydrate diet, body weight assessment (body scale (BS)) with a low-carbohydrate diet, and low-carbohydrate diet only. Primary outcome was the change in fat mass and secondary outcomes were the changes in body weight and body composition. Forty-five participants completed the study (compliance rate: 95.7%). Fat mass was significantly reduced in all three groups (all
< 0.05); however, the greatest reduction in fat mass was observed in the BA group compared to the BS (differences in changes in fat mass, -1.1 kg; 95% confidence interval: -2.3, -0.2;
= 0.040) and control (differences in changes in fat mass, -1.3 kg; 95% confidence interval: -2.1, -0.4;
= 0.013) groups. The BA group showed significantly greater reductions in body weight and visceral fat mass than the BS and control groups (all
< 0.05). In addition, the percent body fat and skeletal muscle mass were significantly reduced in both BA and BS groups (all
< 0.05). However, no significant differences were found in changes in body fat percentage and skeletal muscle mass between the study groups. Monitoring BA levels, which could have motivated participants to adhere more closely to the low-carbohydrate diet, to assess body fat oxidation rates may be an effective intervention for reducing body fat mass (compared to body weight assessment or control conditions). This approach could be beneficial for individuals seeking to manage body fat and prevent obesity.
The purpose of our study was to validate a newly developed breath acetone (BrAce) analyzer, and to explore if BrAce could predict aerobic exercise-related substrate use. Six healthy men ran on a ...treadmill at 70% of maximal oxygen consumption (VO
) for 1 h after two days of a low-carbohydrate diet. BrAce and blood ketone (acetoacetate (ACAC), beta-hydroxybutyrate (BOHB)) levels were measured at baseline and at different time points of post-exercise. BrAce values were validated against blood ketones and respiratory exchange ratio (RER). Our results showed that BrAce was moderately correlated with BOHB (
= 0.68,
< 0.01), ACAC (
= 0.37,
< 0.01) and blood ketone (
= 0.60,
< 0.01), suggesting that BrAce reflect blood ketone levels, which increase when fat is oxidized. Furthermore, BrAce also negatively correlated with RER (
= 0.67,
< 0.01). In our multiple regression analyses, we found that when BMI and VO
were added to the prediction model in addition to BrAce, R
values increased up to 0.972 at rest and 0.917 at 1 h after exercise. In conclusion, BrAce level measurements of our BrAce analyzer reflect blood ketone levels and the device could potentially predict fat oxidation.
OBJECTIVEWe examined the effects of short-term KD on exercise efficiency and hormonal response during and after the graded exercise testing. METHODSFourteen untrained healthy adults (8 males, 6 ...females, age 26.4 ± 3.1 SD years; BMI 24.8 ± 4.6 kg/m2; peak VO2max 54.0 ± 5.8 ml/kg FFM/min) completed 3-days of a mixed diet (MD) followed by another 3-days of KD after 3-days of washout period. Upon completion of each diet arm, participants underwent graded exercise testing with low- (LIE; 40% of VO2max), moderate- (MIE; 55%), and high-intensity exercise (HIE; 70%). Exercise efficiency was calculated as work done (kcal/min)/energy expenditure (kcal/min). RESULTSFat oxidation during the recovery period was higher in KD vs. MD. Despite identical workload during HIE, participants after having KD vs. MD showed higher energy expenditure and lower exercise efficiency (10.1 ± 0.7 vs. 12.5 ± 0.3%, p < .01). After KD, free fatty acid (FFA) concentrations were higher during MIE and recovery vs. resting, and beta-hydroxybutylate (BOHB) was lower at HIE vs. resting. Cortisol concentrations after KD was higher during recovery vs. resting, with no significant changes during graded exercise testing after MD. CONCLUSIONSOur data suggest that short-term KD is favorable to fat metabolism leading increased circulating FFA and BOHB during LIE to MIE. However, it is notable that KD may cause 1) exercise inefficiency manifested by increased energy expenditure and 2) elevated exercise stress during HIE and recovery. Trial registration: KCT0005172, International Clinical Trials Registry Platform.
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