In the present work, single-phase CuO particles were synthesized by a hydrothermal method and characterized by SEM, TEM and XRD. The gas sensing properties of the CuO based sensor to some representative flammable VOC gases such as ethanol, isopropanol, acetone, benzene, para-xylene and decane were investigated. The sensor resistance increased when exposed to these flammable analytes, as well as when the concentration of oxygen in air decreased. That phenomenon is attributed to the surface accumulation conduction mechanism of the p-type metal oxide semiconductor, when negatively charged surface oxygen desorbs from the surface of CuO and releases electrons back to the CuO bulk. According to our research, the detection limit of the CuO based sensor to decane was better than 1 ppm, which indicated the potential applications of CuO based sensors in detecting low concentration decane.

Methoxy propanol has been widely used in modern industry and consumer products. Inhalation or skin exposure to methoxy propanol for a long period would bring about safety challenges on human habitat and health. Ag decorated SnO₂ mesoporous material has been synthesized and shown to exhibit high sensitivity and good selectivity to methoxy propanol among other interferential VOC gases. Density Functional Theory study were conducted to yield insight into the surface–adsorbate interactions and therefore the gas sensing improvement mechanism by presenting accurate energetic and electronic properties for the Ag/SnO₂ system. Firstly, an electron transfer model on Ag and SnO₂ grain interface was put forward to illustrate the methoxy propanol gas sensing mechanism. Then, a three-layer adsorption model (TLAM) was proposed to investigate methoxy propanol gas sensing properties on a SnO₂ (110) surface. In the TLAM method, taking SnO₂ (110) surface for the basis, layer 1 illustrates the decoration of metal Ag on SnO₂ (110) surface. Layer 2 represents the adsorption of molecular oxygen on metal Ag decorated SnO₂ (110) surface. Layer 3 indicates the adsorption of methoxy propanol, and for comparison, three other VOC gases (namely, ethanol, isopropanol and p-xylene) on Ag decorated SnO₂ (110) surface with oxygen species pre-adsorbed consecutively. All the adsorption processes were calculated by means of Density Functional Theory method; the adsorption energy, net charge transfer, DOS, PDOS and also experimental data were utilized to investigate the methoxy propanol gas sensing mechanism on Ag decorated SnO₂ (110) surface with oxygen species pre-adsorbed.

Sweat collection and real time monitoring of sweat rate play essential roles in physiology monitoring and assessment of an athlete’s performance during exercise. In this paper, we report a micropump for sweat simulant collection based on the capillary–evaporation effect. An electrochemical sensor is integrated into the micropump, which monitors the flow rate in real-time by detecting the current using three electrodes. The evaporation rate from micropore array, equivalent to the sweat rate, was theoretically and numerically investigated. The designed micropump yields the maximum collection rate as high as 0.235 $\mathsf{\mu }$ L/min. In addition, the collection capability of the micropump was validated experimentally; the flow rate through the microchannel was further detected in real-time with the electrochemical sensor. The experimental maximum collection rate showed good consistency with the theoretical data. Our proposed device shows the potential for sweat collection and real-time monitoring of sweat rate, which is a promising candidate for being a wearable platform for real-time physiology and performance monitoring during exercise.

Flexible pressure sensors are widely applied in tactile perception, fingerprint recognition, medical monitoring, human–machine interfaces, and the Internet of Things. Among them, flexible capacitive pressure sensors have the advantages of low energy consumption, slight signal drift, and high response repeatability. However, current research on flexible capacitive pressure sensors focuses on optimizing the dielectric layer for improved sensitivity and pressure response range. Moreover, complicated and time-consuming fabrication methods are commonly applied to generate microstructure dielectric layers. Here, we propose a rapid and straightforward fabrication approach to prototyping flexible capacitive pressure sensors based on porous electrodes. Laser-induced graphene (LIG) is produced on both sides of the polyimide paper, resulting in paired compressible electrodes with 3D porous structures. When the elastic LIG electrodes are compressed, the effective electrode area, the relative distance between electrodes, and the dielectric property vary accordingly, thereby generating a sensitive pressure sensor in a relatively large working range (0–9.6 kPa). The sensitivity of the sensor is up to 7.71%/kPa⁻¹, and it can detect pressure as small as 10 Pa. The simple and robust structure allows the sensor to produce quick and repeatable responses. Our pressure sensor exhibits broad potential in practical applications in health monitoring, given its outstanding comprehensive performance combined with its simple and quick fabrication method.