The
high moisture level of exhaled gases unavoidably limits the
sensitivity of breath analysis via wearable bioelectronics. Inspired
by pulmonary lobe expansion/contraction observed during respiration,
a respiration-driven triboelectric sensor (RTS) was devised for simultaneous
respiratory biomechanical monitoring and exhaled acetone concentration
analysis. A tin oxide-doped polyethyleneimine membrane was devised
to play a dual role as both a triboelectric layer and an acetone sensing
material. The prepared RTS exhibited excellent ability in measuring
respiratory flow rate (2–8 L/min) and breath frequency (0.33–0.8
Hz). Furthermore, the RTS presented good performance in biochemical
acetone sensing (2–10 ppm range at high moisture levels), which
was validated via finite element analysis. This work has led to the
development of a novel real-time active respiratory monitoring system
and strengthened triboelectric–chemisorption coupling sensing
mechanism.
Aerosol deposition (AD) is a novel ceramic film preparation technique exhibiting the advantages of room-temperature operation and highly efficient film growth. Despite these advantages, AD has not been used for preparing humidity-sensing films. Herein, room-temperature AD was utilized to deposit BaTiO films on a glass substrate with a Pt interdigital capacitor, and their humidity-sensing performances were evaluated in detail, with further optimization performed by postannealing at temperatures of 100, 200, ..., 600 °C. Sensor responses (i.e., capacitance variations) were measured in a humidity chamber for relative humidities (RHs) of 20-90%, with the best sensitivity (461.02) and a balanced performance at both low and high RHs observed for the chip annealed at 500 °C. In addition, its response and recovery were extremely fast, respectively, at 3 and 6 s and it kept a stable recording with the maximum error rate of 0.1% over a 120 h aging test. Compared with other BaTiO-based humidity sensors, the above chip required less thermal energy for its preparation but featured a more than 2-fold higher sensitivity and a superior detection balance at RHs of 20-90%. Cross-sectional transmission electron microscopy imaging revealed that the prepared film featured a transitional variable-density structure, with moisture absorption and desorption being promoted by a specific capillary structure. Finally, a bilayer physical model was developed to explain the mechanism of enhanced humidity sensitivity by the prepared BaTiO film.
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