Development of a Low-Cost Portable Electronic Nose for Cigarette Brands Identification.

In China, the government and the cigarette industry yearly lose millions in sales and tax revenue because of imitation cigarettes. Usually, visual observation is not enough to identify counterfeiting. An auxiliary analytical method is needed for cigarette brands identification. To this end, we developed a portable, low-cost electronic nose (e-nose) system for brand recognition of cigarettes. A gas sampling device was designed to reduce the influence caused by humidity fluctuation and the volatile organic compounds (VOCs) in the environment. To ensure the uniformity of airflow distribution, the structure of the sensing chamber was optimized by computational fluid dynamics (CFD) simulations. The e-nose system is compact, portable, and lightweight with only 15 cm in side length and the cost of the whole device is less than $100. Results from the machine learning algorithm showed that there were significant differences between 5 kinds of cigarettes we tested. Random Forest (RF) has the best performance with accuracy of 91.67% and K Nearest Neighbor (KNN) has the accuracy of 86.98%, which indicated that the e-nose was able to discriminate samples. We believe this portable, cheap, reliable e-nose system could be used as an auxiliary screen technique for counterfeit cigarettes.

Chinese health literacy scale for tuberculosis patients: a study on development and psychometric testing.

BACKGROUND: The role of health literacy on tuberculosis patients has not been evaluated in China, in part because few special health literacy measurements exist. METHODS: A three-step design process was used: (1) Scale construction: Based on the model of revised Bloom's taxonomy, the item-pool was drafted from a literature review, focus group discussion, and in-depth interviews. In addition, a Delphi survey was used in order to select items for inclusion in the scales; (2) Pilot study: Acceptability and clarity were tested with 60 tuberculosis patients; and (3) Psychometric testing: Validity analysis includes content validity, construct validity, and discriminative validity. The Cronbach's alpha coefficient, split-half reliability, and test-retest method were used to assess reliability. Finally, a receiver operating characteristic analysis was conducted to generate a cut-off point. RESULTS: The final scale had 29 items with four domains. The item level Content Validity Index ranged from 0.70 to 1.0, and the scale level Content Validity Index was 0.95. The mean score among the lowest 27% group was significantly lower than that those of the highest 27% group (p < 0.01), which supports adequate discriminant validity. Explanatory factor analysis produced a clear four-factor construct, explaining 47.254% of the total variance. Factor 1 and Factor 2 were consistent with read and memorize TB-related words; Factor 3 was associated with understand the meaning of the health education leaflets and examine if TB patients can apply the correct approach to correct context; Factor 4 was related to the ability of TB patient to calculate and identify what unspecified assumptions are included in known conditions. The confirmatory factory analysis results confirmed that a four-factor model was an acceptable fit to the data, with a goodness-of-fit index = 0.930, adjusted goodness of fit index = 0.970, root mean square error of approximation = 0.069, and χ2/df = 2.153. The scale had good internal consistency and test-retest reliability. Additionally, the receiver operating characteristic analysis indicated that the cut-off point for the instrument was set at 45 and 35. CONCLUSIONS: The Chinese Health Literacy scale for Tuberculosis has good reliability and validity, and it could be used for measuring the health literacy of Chinese patients with tuberculosis.

WO3 nanolamella gas sensor: porosity control using SnO2 nanoparticles for enhanced NO2 sensing.

Tungsten trioxide (WO3) is one of the important multifunctional materials used for photocatalytic, photoelectrochemical, battery, and gas sensor applications. Nanostructured WO3 holds great potential for enhancing the performance of these applications. Here, we report highly sensitive NO2 sensors using WO3 nanolamellae and their sensitivity improvement by morphology control using SnO2 nanoparticles. WO3 nanolamellae were synthesized by an acidification method starting from Na2WO4 and H2SO4 and subsequent calcination at 300 °C. The lamellae were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), which clearly showed the formation of single-crystalline nanolamellae with a c-axis orientation. The stacking of each nanolamella to form larger lamellae that were 50-250 nm in lateral size and 15-25 nm in thickness was also revealed. From pore size distribution measurements, we found that introducing monodisperse SnO2 nanoparticles (ca. 4 nm) into WO3 lamella-based films improved their porosity, most likely because of effective insertion of nanoparticles into lamella stacks or in between assemblies of lamella stacks. In contrast, the crystallite size was not significantly changed, even by introducing SnO2. Because of the improvement in porosity, the composites of WO3 nanolamellae and SnO2 nanoparticles displayed enhanced sensitivity (sensor response) to NO2 at dilute concentrations of 20-1000 ppb in air, demonstrating the effectiveness of microstructure control of WO3 lamella-based films for highly sensitive NO2 detection. Electrical sensitization by SnO2 nanoparticles was also considered.

Discriminative Detection of Different Cigarette Brands Using a Fast-Response Electronic Nose.

Electronic noses are an artificial olfactory system that mimics the animal olfactory function. Currently, metal oxide semiconductor (MOS) gas sensors play a vital role in the development of high-performance electronic noses and have widespread applications across various fields. They are particularly valuable in ensuring food safety, monitoring air quality, and even detecting explosives for antiterrorism purposes. However, there is an increasing demand for electronic noses to exhibit faster response times in large-scale commercial applications. To address this challenge, we developed a novel MOS gas sensor with a porous ceramic substrate, specifically designed to facilitate rapid gas diffusion. The sensing performance of the sensor array was evaluated and the result showed that the T90 time of porous ceramic-assisted MOS sensor was significantly (57%) shorter than sensors with a normal substrate. Moreover, the electronic nose system had demonstrated remarkable capability in accurately distinguishing between five distinct types of hazardous gases, including VOCs as well as ammonia. Furthermore, a low-cost electronic system was developed and applied to cigarette brand identification; 2490 groups of data were collected for each individual test at only a cost of 20 s. By employing a machine learning algorithm to analyze the data, an accuracy higher than 95% was achieved (96.29% for K nearest neighbor and 96.32% for random forest). We found that our system can resolve the onset time of electronic nose measurement with enough precision, and it was expected that this special approach by using porous ceramic as an insulating substrate can provide a simple and reliable method to manufacture a fast-response electronic nose.

Ferroelectric Polarization and Oxygen Vacancy Synergistically Induced an Ultrasensitive and Fast Humidity Sensor for Multifunctional Applications.

With the arrival of the Internet of Things and artificial intelligence, humidity sensors monitoring water emissions from human metabolism have attracted great attention in the fields of smart wearable devices and noncontact human-machine interaction. However, their application is seriously limited by the trade-off between the sensitivity and response speed for traditional humidity sensors. Herein, to overcome it, a self-powered high performance humidity sensor is developed on the basis of the electric-poled and oxygen vacancy-rich BiFeO3 (BFO) ferroelectric material. The synergistic effect of ferroelectric polarization and oxygen vacancy provides a strong driving force and active adsorption sites for an abundance of OH/H2O adsorption, resulting in an ultrahigh response (∼104) and ultrafast response/recovery speed (∼84/376 ms). Benefiting from its promising advantages, the wearable humidity sensor can accurately record the respiration rate/depth and recognize different human respiratory behaviors in real-time. Importantly, by utilizing the moisture from mouth-blowing and skin, the sensors are successfully applied to noncontact control of a robotic car, noncontact switch, and noncontact interface for visualization applications. This work provides an effective strategy for developing excellent humidity sensors that meet the requirement of noncontact interaction for next-generation intelligent electronics.

Practical and Efficient: A Pocket-Sized Device Enabling Detection of Formaldehyde Adulteration in Vegetables.

Formaldehyde, as a carcinogenic substance, is often intentionally used to adulterate vegetables to increase their shelf life, and the adhesive tape used to attach labels can also leave formaldehyde on the surface of vegetables. However, as the "gold" standard, gas chromatography (GC) and high-performance liquid chromatography (HPLC) are expensive for individual tests and confined to the laboratory owing to their size and a suitable detector (low-cost, portable, fast detection speed) to check formaldehyde contamination in vegetables not being available. Here, we tested formaldehyde contamination in vegetables using a low-cost and hand-held detector combined with a screen-printed electrode (SPE) amperometric sensor and an open-sourced potentiostat. The analyzer can detect a concentration of 100 µmol/L formaldehyde and achieve a good linear range between 100 and 1000 µmol/L. Furthermore, the detector successfully identified formaldehyde contamination in 53 samples of six different kinds of vegetables even after residual formaldehyde on the surface was evaporated. Most importantly, under the practicability-oriented idea, a cost-effective strategy was implemented for this detector design rather than using other pricey methods (e.g., photolithography, electron-beam evaporation, chemical deposition), which enormously reduces the cost (under ∼USD 0.5 per test) and meets all of the requirements of ASSURED device. We believe this cheap, portable detector could help law-enforcing authorities, healthcare workers, and customers to screen formaldehyde contamination easily. Also, the cost-saving strategy is appropriate for low-income areas, where there is a lack of laboratories, funds, and trained experts.

Amperometric Hydrogen Sensor Based on Solid Polymer Electrolyte and Titanium Foam Electrode.

Trace hydrogen detection plays an important role in the safety detection of lithium-ion batteries (LIBs) due to the generation and leakage of trace hydrogen in the early stage of LIBs damage. In this work, an amperometric hydrogen sensor based on solid polymer electrolyte was reported. The sandwich device structure was realized, which could directly diffuse the gas from both sides to the three-phase interface (gas/electrode/electrolyte) to participate in the reaction through the optimal design of the gas diffusion path. Then, platinum nanoparticles (Pt-NPs) were loaded on the metal foam by electroplating, and the porous electrode was filled with solid polymer electrolyte. A sensor with high specific surface area, high catalytic activity, and high sensitivity was obtained. Finally, the hydrogen oxidation reaction (HOR) mechanism of the platinum-loaded (Pt-loaded) titanium foam (Ti foam) electrode under both anaerobic and aerobic conditions was verified, and the properties of the sensor was evaluated. The hydrogen sensor with a "sandwich" structure has the advantages of high sensitivity, good stability, low detection limit and low cost, which provides a technical solution for the safety and real-time monitoring of LIBs.

Distribution of bacteriologically positive and bacteriologically negative pulmonary tuberculosis in Northwest China: spatiotemporal analysis.

Pulmonary tuberculosis (PTB) is a major health issue in Northwest China. Most previous studies on the spatiotemporal patterns of PTB considered all PTB cases as a whole; they did not distinguish notified bacteriologically positive PTB (BP-PTB) and notified bacteriologically negative PTB (BN-PTB). Thus, the spatiotemporal characteristics of notified BP-PTB and BN-PTB are still unclear. A retrospective county-level spatial epidemiological study (2011-2018) was conducted in Shaanxi, Northwest China. In total, 44,894 BP-PTB cases were notified, with an average annual incidence rate of 14.80 per 100,000 persons between 2011 and 2018. Global Moran's I values for notified BP-PTB ranged from 0.19 to 0.49 (P < 0.001). Anselin's local Moran's I analysis showed that the high-high (HH) cluster for notified BP-PTB incidence was mainly located in the southernmost region. The primary spatiotemporal cluster for notified BP-PTB (LLR = 612.52, RR = 1.77, P < 0.001) occurred in the central region of the Guanzhong Plain in 2011. In total, 116,447 BN-PTB cases were notified, with an average annual incidence rate of 38.38 per 100,000 persons between 2011 and 2018. Global Moran's I values for notified BN-PTB ranged from 0.39 to 0.69 (P < 0.001). The HH clusters of notified BN-PTB were mainly located in the north between 2011 and 2014 and in the south after 2015. The primary spatiotemporal cluster for notified BN-PTB (LLR = 1084.59, RR = 1.85, P < 0.001) occurred in the mountainous areas of the southernmost region from 2014 to 2017. Spatiotemporal clustering of BP-PTB and BN-PTB was detected in the poverty-stricken mountainous areas of Shaanxi, Northwest China. Our study provides evidence for intensifying PTB control activities in these geographical clusters.

Electronic Nose Based on Temperature Modulation of MOS Sensors for Recognition of Excessive Methanol in Liquors.

An electronic nose based on metal oxide semiconductor (MOS) sensors has been used to identify liquors with excessive methanol. The technique for a square wave temperature modulated MOS sensor was applied to generate the response patterns and a back-propagation neural network was used for pattern recognition. The parameters of temperature modulation were optimized according to the difference in response features of target gases (methanol and ethanol). Liquors with excessive methanol were qualitatively and quantitatively identified by the neural network. The results showed that our electronic nose system could well identify the liquors with excessive methanol with more than 92% accuracy. This electronic nose based on temperature modulation is a promising portable adjunct to other available techniques for quality assurance of liquors and other alcoholic beverages.

MXene-Derived TiO2 Nanoparticles Intercalating between RGO Nanosheets: An Assembly for Highly Sensitive Gas Detection.

Tight stacking between two-dimensional (2D) sheet-like materials, such as graphene, in the solid state is a major challenge hindering their applications, especially in the gas sensing field. Here, we report on a TiO2 nanoparticle-spaced reduced graphene oxide (RGO) assembly for the design of highly sensitive gas sensors. The TiO2 nanospacers are derived from a 2D MXene that is intercalated between RGO sheets. The produced TiO2-spaced RGO assembly exhibits a uniform nanoparticle distribution and highly wrinkled RGO sheets that interconnect in micrometer-scale pores. The space limitation between adjacent RGO sheets can restrict the particle growth and lead to the formation of TiO2 nanoparticles with uniform diameters of ca. 6.2 nm. The sensitivity of the TiO2-spaced RGO sensor to NO2 improved by over 400% in comparison with pure RGO due to the more available surface area and active adsorption sites. Furthermore, fast response and recovery, excellent selectivity and flexibility, and reliable workability in a humid environment (with the relative humidity ranging from 5 to 95%) were also simultaneously achieved, demonstrating great potential for next-generation wearable sensors.

Global, regional, and national prevalence of diabetes mellitus in patients with pulmonary tuberculosis: a systematic review and meta-analysis.

BACKGROUND: Both pulmonary tuberculosis (PTB) and diabetes mellitus (DM) are major global public health problems. We estimated the global, regional, and national prevalence of diabetes mellitus in a population with PTB. METHODS: We searched for observational studies of DM in people with PTB using the PubMed and Embase electronic bibliographic databases, focusing on articles published in the English language from database inception until March 31, 2021. We included original research that reported the prevalence of DM in PTB or those that had sufficient data to compute these estimates. Studies were excluded if they did not provide primary data or were case studies or reviews. Two authors independently extracted the articles and collected detailed information using a predefined questionnaire. A country-specific random-effects meta-analysis was used for countries with two or more available studies, and a fractional response regression model was employed to predict the prevalence of DM in PTB for countries with one or no study. The study was registered with the International Prospective Register of Systematic Reviews, using the registration number CRD42018101989. RESULTS: We identified 22,658 studies, and 153, across 51 countries, were retained for data extraction. The global prevalence of DM among patients with PTB was estimated to be 13.73% (95% confidence interval [CI] 12.51-14.95). The prevalence rates were 19.32% (95% CI 13.18-25.46) in the region of the Americas, 17.31% (95% CI 12.48-22.14) in the European region, 14.62% (95% CI 12.05-17.18) in Southeast Asia, 13.59% (95% CI 7.24-19.95) in the western Pacific region, 9.61% (95% CI 4.55-14.68) in the eastern Mediterranean region, and 9.30% (95% CI 2.83-15.76) in the African region. The country with the highest estimated prevalence was the Marshall Islands (50.12%; 95% CI 4.28-95.76). CONCLUSION: Comorbid PTB and DM remain prevalent worldwide.

Triazine-Based Two-Dimensional Organic Polymer for Selective NO2 Sensing with Excellent Performance.

Gas sensors with high sensitivity, fast response/recovery, good selectivity, and room-temperature operation are highly desirable for practical use. However, most of the existing gas sensing materials, either conventional metal oxide semiconductors or advanced inorganic two-dimensional (2D) polymers, can hardly satisfy the above requirements. Herein, we demonstrate an organic 2D polymer derived from a covalent triazine framework (CTF), which possesses nanoscale thickness, intrinsic and periodic pore structures, and abundant functional groups with excellent gas sensing performance. The as-prepared triazine-based 2D polymer (T-2DP) exhibits selective recognition to NO2 with an ultrahigh sensitivity of 452.6 ppm-1, which outperforms most other 2D nanomaterials and its CTF matrix. The sensing effect is superfast (35-47 s) and fully reversible operated at room temperature. The superior comprehensive gas sensing performance of T-2DP and the underlying mechanism was experimentally studied and further discussed by comparison with that of CTF and widely investigated inorganic 2D polymers including graphene and MXene. As a proof of concept, a flexible NO2 chemiresistor based on T-2DP was fabricated to demonstrate its potential for integration into wearable electronics. The scientific findings in this work may propose a new route for the design of high-performance gas sensing materials on the basis of organic 2D polymers in next-generation wearable electronic devices.

Developing and Validating an Adjustment Scale: The Adaptation Status Assessment of Drug-Resistant Tuberculosis Patients.

PURPOSE: Drug-resistant tuberculosis (DR-TB) remains a major global public health issue. For DR-TB patients, effective adaptation is crucial to prevent disease progression, improve health outcomes and decrease mortality. To date, there is no appropriate tool for evaluating the adaptation status of DR-TB patients. In this work, we aim to develop an adjustment scale for DR-TB patients (AS-DRTBP) and to evaluate its psychometric properties. PATIENTS AND METHODS: The development of the AS-DRTBP was based on the theory of the Roy adaptation model (RAM). The scale was designed through a literature review, in-depth individual interviews, a Delphi survey, and pilot testing. In total, 433 patients with DR-TB were recruited to validate the instrument. The split-half reliability coefficient, Cronbach's alpha coefficient, and test-retest reliability coefficient were calculated to assess the reliability of the instrument. Content validity, construct validity and concurrent validity tests were applied to calculate the validity of the instrument. RESULTS: The final AS-DRTBP consisted of four dimensions and 26 items. The Cronbach's alpha coefficient, split-half reliability coefficient and test-retest reliability coefficient were 0.893, 0.954, and 0.853, respectively. The content validity index was 0.92. Four factors that explained 64.605% of the total variance were also further determined by confirmatory factor analysis (CFA). The CFA results showed that the fitting effect of the model was appropriate (CMIN/DF = 1.681, GFI = 0.832, AGFI = 0.799, RMSEA = 0.055, SRMR = 0.0684). The AS-DRTBP and adjustment scale had correlation in the total score, and the correlation coefficient was 0.355 (p<0.05). CONCLUSION: The findings of this study demonstrate that the AS-DRTBP is a reliable and valid instrument for measuring the adaptation status of patients with DR-TB, allowing health providers to comprehend the adaptive level of DR-TB patients and thus laying the foundation for interventions to help these patients achieve a physiologically, psychologically and socially optimal outcome.

Efficient NH3 Detection Based on MOS Sensors Coupled with Catalytic Conversion.

A solution of NH3 detection based on catalytic conversion of NH3 into NOx was proposed by using MOS gas detectors and Pt-supported catalysts. The catalysts convert NH3 into NOx, which is a very sensitive analyte for MOS detectors. Catalysts based on Pt-loaded HZSM-5 and Al2O3 were prepared by wet impregnation. MOS detectors were fabricated from nanosized In2O3 and WO3 using screen-printing techniques. As expected, MOS sensors based on In2O3 and WO3 have an extremely high sensitivity to NO2; nevertheless, they have a relatively low response to NH3 and a large cross-sensitivity to typical interfering gases such as CO and ethanol. By the present solution, MOS sensors could very sensitively respond to NH3, even down to 0.25 ppm. In addition, it was also found that the catalysis also combusts the reducing gases into CO2 and water and consequently significantly improves the selectivity of NH3. Lastly, we would to like to stress that the proposed concept of the catalytic conversion method suggests the potential utility for broader measurements by using different catalysts and gas detectors and that only a part of the usage for NH3 was presented here.

Effect of Parental Migration on the Intellectual and Physical Development of Early School-Aged Children in Rural China.

OBJECTIVE: The purpose of this study is to estimate the effect of parent migration on intellectual and physical development of early school-aged children in rural China. DESIGN: setting and participants: The present cross-sectional study participants were a subset from a controlled, cluster-randomized, double-blind trial. From October 2012 to September 2013, the offspring of women who participated in a large trial were examined in the present study. Wechsler intelligence scale for children (WISC-IV) in which validity and reliability were shown to be satisfactory was used to measure the intellectual function and trained anthropometrists measured weight and height of children using standard procedures. RESULTS: The mean difference of FSIQ scores between non-migration and both-parent migration groups was -3.68 (95%CI: -5.49, -1.87). After adjusting for the confounders, the mean difference of full-scale IQ between non-migration and both-parent migration group was -1.97 (95%CI: -3.92, -0.01), the mean differences of perceptual reasoning index and processing speed index were -2.41 (95%CI: -4.50, -0.31) and -2.39 (95%CI: -4.42, -0.35) between two groups respectively. CONCLUSION: Our results emphasized the impairment of both-parental migration in intellectual function (FSIQ, PRI, PSI) of children. These findings have important policy implications for the Chinese government to prevent the impairment of left-behind children. Further research is required to clarify the mechanisms by which both-parental migration influence the impairment in intellectual function of children.

NO2 Sensing Properties of Cr2WO6 Gas Sensor in Air and N2 Atmospheres.

Gas sensors were fabricated from Cr2WO6 nanoparticles for NO2 detection. Low dimensional materials Cr2WO6 were prepared by a wet chemistry method followed by hydrothermal treatment. The morphology of the nanoparticles and their sensing properties to NO2 were investigated in both dry and humid conditions. Additionally, the sensing response was also characterized in a non-oxygen condition. It was concluded that the sensor responses in N2 conditions were higher than that in air conditions at 200°C. Moreover, the sensing characteristics were inhibited by water vapor at 200°C. The oxygen adsorption behavior was also investigated to verify the basic sensing mechanism of Cr2WO6 in the absence and presence of NO2 and water vapor separately. Based on the power law response, it was indicated that both NO2 and water vapor have a strong adsorption ability than oxygen ions of Cr2WO6 sensors.

Development And Preliminary Evaluation Of Psychometric Properties Of A Tuberculosis Self-Efficacy Scale (TBSES).

PURPOSE: No instrument exists for measuring TB patients' self-efficacy which is vital for choosing and insisting in benefit TB-management behaviors. Our study aimed to develop and test a new tuberculosis self-efficacy scale (TBSES). PATIENTS AND METHODS: The TBSES was designed through literature review, individual interviews, Delphi surveys, and pilot testing. After that, 460 TB patients were recruited to validate TBSES. Exploratory and confirmatory factor analysis and correlation analysis were used to evaluate the scale reliability and validity. The cut-off point for TBSES was identified using receiver operating characteristic (ROC) analysis. RESULTS: The final TBSES includes 21 items scored on a 5-point Likert scale, and these items are loaded in four distinct factors that explain 67.322% of the variance, both exploratory and confirmatory factor analysis proved that the scale had good construct validity. The scale had adequate internal consistency, split-half reliability, test-retest reliability, as well as demonstrated content, concurrent validity. The ROC analysis results showed the cut-off point was 86.5. CONCLUSION: This 21-item TBSES demonstrated favorable psychometric properties. It provides an instrument for not only measuring specific self-efficacy in TB, but also identifying patients with low self-efficacy and determining the specific area toward designing interventions for enhance self-efficacy.

Perceptions of engagement in health care among patients with tuberculosis: a qualitative study.

PURPOSE: Adherence to treatment is cited as a key challenge in fighting tuberculosis (TB). Treatment of TB requires patients to actively engage in their care. The purpose of this study was to explore the perceptions of patients with TB regarding their engagement in health care. PATIENTS AND METHODS: The study was conducted in three medical wards in one hospital. Purposive sampling was used to recruit participants. Semi-structured, audiotaped interviews were conducted and analyzed using thematic analysis. RESULTS: Twenty-three patients participated in the study. Four major themes emerged: 1) devaluing engagement; 2) interacting with health care providers (HCPs); 3) facing inability; and 4) seeking external support. CONCLUSION: The patients' perceptions of their engagement in health care were generally negative. Paying attention to the preferences and needs of patients and making decisions accordingly are effective strategies for promoting patient engagement. Moreover, HCPs should be aware of their crucial role in helping patients make sense of what engagement is and how to engage. In the process of engagement, providers should establish effective interactions with patients and cooperate with family and peers.

Acetone Sensing Properties and Mechanism of Rh-Loaded WO3 Nanosheets.

WO3 nanosheets was prepared by an acidification method and the Rh catalyst was dispersed on the surface of the nanosheets with a wet impregnation method. The morphology of pristine WO3 and Rh modified WO3 nanosheets and their responses to acetone gas were studied. According to oxygen adsorption combined with TPR results, the sensing and sensitization mechanism of acetone were discussed. It was found that no visible changes in nanostructures or morphologies were observed in WO3 nanosheets with Rh, however, the sensor resistance and sensor response were greatly promoted. The basic sensitization mechanism could be caused by the electronic interaction between oxidized Rh and WO3 surface.

Nanoparticle cluster gas sensor: controlled clustering of SnO2 nanoparticles for highly sensitive toluene detection.

Gas sensing with nanosized oxide materials is attracting much attention because of its promising capability of detecting various toxic gases at very low concentrations. In this study, using clustered SnO2 nanoparticles formed by controlled particle aggregation, we fabricated highly sensitive gas sensing films to detect large gas molecules such as toluene. A hydrothermal method using stanic acid (SnO2·nH2O) gel as a precursor produced monodispersed SnO2 nanoparticles of ca. 5 nm at pH 10.6. Decreasing the solution pH to 9.3 formed SnO2 clusters of ca. 45 nm that were assemblies of the monodispersed nanoparticles, as determined by dynamic light scattering, X-ray diffraction, and transmission electron microscopy analyses. Porous gas sensing films were successfully fabricated by a spin-coating method using the clustered nanoparticles due to the loose packing of the larger aggregated particles. The sensor devices using the porous films showed improved sensor responses (sensitivities) to H2 and CO at 300 °C. The enhanced sensitivity resulted from an increase in the film's porosity, which promoted the gas diffusivity of the sensing films. Pd loading onto the clustered nanoparticles further upgraded the sensor response due to catalytic and electrical sensitization effects of Pd. In particular, the Pd-loaded SnO2 nanoparticle clusters showed excellent sensitivity to toluene, able to detect it at down to low ppb levels.