Many studies have identified tungsten trioxide (WO 3 ) as a promising candidate for optical gas sensing applications. WO 3 , coated with thin catalytic metals such as Pd , was reported to show a color change from transparent to dark blue upon exposure to oxidizing gas such as hydrogen (H 2 ). Reliable hydrogen sensor is widely used in medical and energy application area. In this work, WO 3 nanostructured thin films were deposited onto sapphire substrates via pulsed laser deposition (PLD) technique by using ArF Excimer laser operating at very short wavelength of 193 nm, the shortest wavelength used in the fabrication of semiconductor oxide thin films. By ablating the target oxides by high energy photons, we could fabricate good crystalline nanostructure thin films. Electron microscopy studies revealed that the uniform and homogeneous WO 3 nanostructured films consist of nanorods of about 50 nm sizes. XRD and Raman studies verified good crystalline formation. Absorbance response toward H 2 gas was investigated for a WO 3 film coated with 25 Å thick palladium (Pd). The Pd/WO 3 nanostructured thin films exhibited excellent gasochromic response toward H 2 when measured in the visible-NIR range at 100°C. As low as 0.06% H 2 concentration was clearly sensed. The larger dynamic response was measured at NIR wavelength of 900 nm as compared to the response at visible wavelength of 500 nm. The dynamic response of the films observed in the range of 500–800 nm showed more significant response toward H 2 with low concentrations (0.06%–1%) than the one at single wavelength. As a result, H 2 with very low concentration was able to be sensed reliably in real time. The response and recovery times were found to be < 2 min. The results indicated that the Pd/WO 3 nanorod films on sapphire substrates responded to very low H 2 concentration (0.06%) which is well below its lower explosive level threshold (4%).
Nanoporous Nb2O5 has been previously demonstrated to be a viable electrochromic material with strong intercalation characteristics. Despite showing such promising properties, its potential for optical gas sensing applications, which involves the production of ionic species such as H+, has yet to be explored. Nanoporous Nb2O5 can accommodate a large amount of H+ ions in a process that results in an energy bandgap change of the material which induces an optical response. Here, we demonstrate the optical hydrogen gas (H2) sensing capability of nanoporous anodic Nb2O5 with a large surface-to-volume ratio prepared via a high temperature anodization method. The large active surface area of the film provides enhanced pathways for efficient hydrogen adsorption and dissociation, which are facilitated by a thin layer of Pt catalyst. We show that the process of H2 sensing causes optical modulations that are investigated in terms of response magnitudes and dynamics. The optical modulations induced by the intercalation process and sensing properties of nanoporous anodic Nb2O5 shown in this work can potentially be used for future optical gas sensing systems.
Summary Background Intestinal gases are currently used for the diagnosis of disorders including small intestinal bacterial overgrowth and carbohydrate malabsorption. Aim To compare the performance of measuring hydrogen production within the gut directly with the telemetric gas‐sensing capsule with that of indirect measurement through breath testing. Methods Using standard breath testing protocols, the capsules and breath tests were simultaneously evaluated in a single‐blinded trial in 12 healthy subjects. Eight received a single dose of 1.25‐40 g inulin and four 20 or 40 g glucose. Safety and reliability of the capsules were also assessed. Results There were no reported adverse events. All capsules were retrieved and operated without failure. Capsule measurements were in agreement with breath test measurements in magnitude but not in timing; minimal hydrogen production was observed after glucose ingestion and capsule measurements correlated with breath hydrogen after ingestion of 40 g inulin. A dose‐dependent increase in concentration of hydrogen was observed from the capsule following ingestion of inulin as low as 1.25 g compared with >10 g for breath measurements. Specifically, the capsule measured >3000 times higher concentrations of hydrogen compared to breath tests, resulting in a signal‐to‐noise ratio of 23.4 for the capsule compared to 4.2 for the breath test. Conclusions The capsule showed high sensitivity and signal‐to‐noise ratio in measuring luminal hydrogen concentrations, provided information on the site of intestinal gas production, and demonstrated safety and reliability. The capsule has potential for improving diagnostic precision for disorders such as small intestinal bacterial overgrowth.
Front Cover In article number 2200429, Zhou, Li, Ou, and co-workers developed a universal ion-exchange and in-situ pyrolysis strategy to co-regulate structural morphologies and chemical contents of metal-organic framework derivatives, achieving enhanced microwave absorption performances.
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