Precise
detection of breath isoprene can provide valuable information
for monitoring the physical and physiological status of human beings
or for the early diagnosis of cardiovascular diseases. However, the
extremely low concentration and low chemical reactivity of breath
isoprene hamper the selective and sensitive detection of isoprene
using oxide semiconductor chemiresistors. Herein, we report that macroporous
WO3 microspheres whose inner macropores are surrounded
by Au nanoparticles exhibit a high response (resistance ratio = 11.3)
to 0.1 ppm isoprene under highly humid conditions at 275 °C and
an extremely low detection limit (0.2 ppb). Furthermore, the sensor
showed excellent selectivity to isoprene over five interferants that
could be exhaled by humans. Notably, the selectivity to isoprene is
critically dependent on the location of Au nanocatalysts and macroporosity.
The mechanism underlying the selective isoprene detection is investigated
in relation to the reforming of less reactive isoprene into more reactive
intermediate species promoted by macroporous catalytic reactors, which
is confirmed by the analysis using a proton transfer reaction quadrupole
mass spectrometer. The sensor for breath analysis has high potential
for simple physical and physiological monitoring as well as disease
diagnosis.
Real-time breath isoprene sensing provides noninvasive methods for monitoring human metabolism and early diagnosis of cardiovascular diseases. Nonetheless, the stable alkene structure and high humidity of the breath hinder sensitive and selective isoprene detection. In this work, we derived well-defined Co 3 O 4 @polyoxometalate yolk−shell structures using a metal− organic framework template. The inner space, including highly catalytic Co 3 O 4 yolks surrounded by a semipermeable polyoxometalate shell, enables stable isoprene to be reformed to reactive intermediate species by increasing the gas residence time and the reaction with the inner catalyst. This sensor exhibited selective isoprene detection with an extremely high chemiresistive response (180.6) and low detection limit (0.58 ppb). The high sensing performance can be attributed to electronic sensitization and catalytic promotion effects. In addition, the reforming reaction of isoprene is further confirmed by the proton transfer reaction−quadrupole mass spectrometry analysis. The practical feasibility of this sensor in smart healthcare applications is exhibited by monitoring muscle activity during the workout.
In article number 1903093, Jong‐Heun Lee and co‐workers describe exclusive detection of sub‐ppm‐level ethylene, a representative plant hormone, using bilayer sensors. The sensor can be widely used for real‐time assessment of fruit freshness/ripening or the control of plant growth/development.
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