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Detecting the acetone in human exhaled breath sensitively and selectively plays an important role in the noninvasive diagnosis of diabetes. However, obtaining a reliable response to ppb level acetone in exhaled breath directly is still a big challenge. Here, an ultrasensitive acetone gas sensor based on p-Rh 2 O 3 -n-ZnO porous heterostructure has been fabricated. The detection limit of the sensor reaches to 50 ppb. The sensor exhibits well repeatability, selectivity and linear response. A good linear relationship between the response and ambient relative humidity is observed. Without removing the water vapor of the exhaled gas, it can distinguish the acetone concentration of the diabetic patients from that of healthy people, implying that the sensor could be used in the diagnosis of diabetes. The synergistic effect of p-Rh 2 O 3 -n-ZnO porous heterostructure makes the sensor own ultrasensitive detecting ability towards acetone. Theoretical models have been built by first-principles calculation to reveal the possible reasons for its ultrasensitivity. It should be pointed out that the much lower adsorption energy (− 1.03 eV) of the acetone molecule on Rh 2 O 3 may be the chief cause of the lower detection limit of the sensor. [Display omitted] • The ultrasensitive gas sensor can detect 50 ppb acetone. • The plots of sensor's response against ambient relative humidity exhibits well linear behavior. • The sensor can distinguish the acetone concentration of the diabetic patients from that of healthy people. • Theoretical models have been built by first-principles calculation to reveal the possible reasons for its ultrasensitivity. [ABSTRACT FROM AUTHOR]

A highly sensitive H 2 gas sensor based on n-WO 3 /p-PdO heterostructure has been fabricated. Using hydrothermal method, through tuning the pH value of the solution, WO 3 nanospindles were synthesized. SEM reveals its uniform morphology; XRD result shows its high crystal quality; N 2 adsorption/desorption result proves its relatively high specific surface area. Through first soaking then calcinating method, PdO was loaded on the surface of WO 3 nanospindles. XPS and HRTEM together have proved the fabrication of the heterostructure between n-WO 3 /p-PdO. The gas sensing device was fabricated by coating the PdO loaded WO 3 paste on a ceramic substrate with silver palladium interdigital electrodes. After loaded into the test chamber, preheated to the required temperature and injecting a certain amount of H 2 , the sensing procedure was done. With optimal ratio of loaded PdO to WO 3 (3 at%), the sensor shows the best gas sensitivity at 150 °C. To 1, 5, 10, 20 and 50 ppm H 2 , the sensor shows the response values (R a /R g) of 1.3, 7, 23, 37 and 76, in the response time of 9s, 8s, 5s, 3s and 1s, respectively. The quasi-one dimensional (QOD) character of WO 3 nanospindle, the well-performance heterostructure between WO 3 and PdO and the optimal ratio of loaded PdO to WO 3 together make the sensor own strong sensing ability towards H 2. The such well-performance H 2 gas sensor based on n-WO 3 /p-PdO heterostructure reminds us that the WO 3 /PdO system has supplied a good material platform to explore the fabrication of ultrasensitive and stable H 2 gas sensor. Image 1 • Quasi-1D WO 3 nanospindles were synthesized by facile hydrothermal method. • P-type PdO with strong catalytic ability to H 2 was loaded on n-type WO 3 nanospindles. • The sensor based on n-WO 3 /p-PdO heterostructure was fabricated. • Towards H 2 , the detection limit of the sensor is 1 ppm, within 9 s. • The H 2 gas sensor shows good stability. [ABSTRACT FROM AUTHOR]