Indirectly
monitoring halitosis via the detection of hydrogen sulfide
(H2S) biomarkers using gas sensors is a newly emerging
technique. However, such H2S sensors are required with
critically high selectivity and sensitivity, as well as a ppb-level
detection limit, which remains technologically challenging. To address
such issues, here, we have developed highly sensitive and selective
H2S sensors with NiO/WO3 nanoparticles (NPs),
which have been synthesized by firstly hydrolyzing WO3 NPs
and subsequently decorating with NiO NPs in a hydrothermal process.
Theoretically, the NiO/WO3 NPs assist in forming a thicker
electron depletion layer, adsorbing more oxygen species O2
– to oxidize H2S and finally release
more electrons. Beneficially, 2.1 wt % NiO/WO3 NPs show
high sensitivity to H2S (R
a/R
g = 15031 ± 1370 @ 10 ppm, 100
°C), which is 42.6-fold higher than that of the pristine WO3 NPs (R
a/R
g = 353 ± 5.6 @ 10 ppm, 100 °C). Further, the H2S sensor shows ppb-level detection limit (R
a/R
g = 4.95 ± 2.9 @ 0.05
ppm, 100 °C) and high selectivity. Practically, NiO/WO3 NP sensor prototype has been employed to detect the simulated exhaled
halitosis compared with that of gas chromatography, revealing a close
concentration of H2S. Our investigation offers an experimental
base in future intelligent medical applications.
Ammonia (NH 3 ) sensors proposed for the simultaneous exhalation diagnosis, environmental pollution monitoring, and industrial leakage alarm require high flexibility, selectivity, stability, humidity tolerance, and wide-concentration-range detection; however, technical challenges still remain. Herein, twistable and water-tolerant paper-based sensors integrated over surgical masks have been developed for NH 3 detection at room temperature, via decorating specially designed ternary nanocomposites (ternary-NCs) on the commercial filter paper. The NCs consist of a multiwalled carbon nanotube framework with a polypyrrole nanolayer and are further loaded with Pt nanodots. Benefiting from the synergy effect of ternary components, the ternary-NCs exhibit an ultrasensitive response to 5 ppb−60 v/v% NH 3 and present high selectivity confirmed by the theory calculations. Remarkably, the filter-paper-based sensors possess outstanding stability against twisting 0−1080°, along with excellent cuttability and foldability. Critically, such paper-based sensors can be integrated over surgical masks for simulated exhaled diagnosis and display superior water tolerance even being immersed in water for 24 h. Practically, the detecting accuracy of the filter-paper-based sensor toward the simulated exhaled NH 3 , environmental NH 3 pollution, and industrial NH 3 leakage is validated using ion chromatography.
Novel mesoporous NiO nanocuboids (M-NiO NCs) enriched with surface multichannel pathways have been achieved to sensitively detect 3H-2B biomarkers for real-time monitoring of Listeria monocytogenes.
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