Here we present a useful ammonia (NH₃) gas sensor based on reduced graphene oxide (RGO)–polyaniline (PANI) hybrids. PANI nanoparticles were successfully anchored on the surface of RGO sheets by using RGO–MnO₂ hybrids as both of the templates and oxidants for aniline monomer during the process of polymerization. The resultant RGO–PANI hybrids were characterized by transmittance electron microscopy, infrared spectroscopy, Raman spectroscopy, UV-Vis spectroscopy, and scanning electron microscopy. The NH₃ gas sensing performance of the hybrids was also investigated and compared with those of the sensors based on bare PANI nanofibers and bare RGO sheets. It was revealed that the synergetic behavior between both of the candidates allowed excellent sensitivity and selectivity to NH₃ gas. The RGO–PANI hybrid device exhibited much better (3.4 and 10.4 times, respectively, with the concentration of NH₃ gas at 50 ppm) response to NH₃ gas than those of the bare PANI nanofiber sensor and bare graphene device. The combination of the RGO sheets and PANI nanoparticles facilitated the enhancement of the sensing properties of the final hybrids, and pave a new avenue for the application of RGO–PANI hybrids in the gas sensing field.

Ultrafast and sensitive room temperature NH3 gas sensors based on chemically reduced graphene oxide (rGO) are demonstrated in this work. rGO, which was prepared via the reduction of graphene oxide by pyrrole, exhibited excellent responsive sensitivity and selectivity to ammonia (NH3) gas. The high sensing performance of these rGO sensors with resistance change as high as 2.4% and response time as fast as 1.4 s was realized when the concentration of NH3 gas was as low as 1?ppb. Furthermore, the rGO sensors could rapidly recover to their initial states with IR illumination. The devices also showed excellent repeatability and selectivity to NH3. These rGO sensors, with low cost, low power, and easy fabrication, as well as scalable properties, showed great potential for ultrasensitive detection of NH3 gas in a wide variety of fields.

We present a useful ammonia gas sensor based on chemically reduced graphene oxide (rGO) sheets by self-assembly technique to create conductive networks between parallel Au electrodes. Negative graphene oxide (GO) sheets with large sizes (>10 μm) can be easily electrostatically attracted onto positive Au electrodes modified with cysteamine hydrochloride in aqueous solution. The assembled GO sheets on Au electrodes can be directly reduced into rGO sheets by hydrazine or pyrrole vapor and consequently provide the sensing devices based on self-assembled rGO sheets. Preliminary results, which have been presented on the detection of ammonia (NH₃) gas using this facile and scalable fabrication method for practical devices, suggest that pyrrole-vapor-reduced rGO exhibits much better (more than 2.7 times with the concentration of NH₃ at 50 ppm) response to NH₃ than that of rGO reduced from hydrazine vapor. Furthermore, this novel gas sensor based on rGO reduced from pyrrole shows excellent responsive repeatability to NH₃. Overall, the facile electrostatic self-assembly technique in aqueous solution facilitates device fabrication, the resultant self-assembled rGO-based sensing devices, with miniature, low-cost portable characteristics and outstanding sensing performances, which can ensure potential application in gas sensing fields.

Graphene is a promising material for gas sensing, but high-performance gas sensors often require a robust structural design in order to endow the resultant sensing devices with batch uniformity, good response, sensitivity, and selectivity. In this study, a novel gas sensor based on assembled porous reduced graphene oxide (rGO) multilayer frameworks was designed and fabricated for gas sensing. To this end, negatively charged holey graphene oxide (GO) and positively charged holey graphene oxide (rGO) were assembled on gold (Au) electrodes through electrostatic interactions to form a porous structural framework. A reduction process was then performed to ensure the formation of a porous framework composed of the r(GO/rGO)_n multilayers. The combined chemical assembly, etching and modification methods resulted in porous r(GO/rGO)_n multilayers with an increased specific surface area. This improved the gas sensor response towards dimethyl methylphosphonate (DMMP) vapour at room temperature. The sensor that was assembled with 12 layers of porous graphene (r(GO/rGO)₁₂) showed a resistance change reaching 8.95% in the presence of 50 ppm DMMP vapour. This value was 3-fold higher than that obtained with the sensor constructed with one-layered graphene. At the low DMMP vapour concentration of 1 ppm, the resistance change in (r(GO/rGO)₁₂) reached a substantial 2.21%. Furthermore, the assembled porous r(GO/rGO)₁₂ sensor showed good repeatability, excellent stability, good uniformity, and elevated selectivity towards DMMP vapour. Overall, the proposed concept looks promising for the design of future high-performance gas sensing devices with broad applications.

The nanosheet stacking phenomenon in graphene thin films significantly deteriorates their gas-sensing performance. This nanosheet stacking issue should be

Continuous monitoring of physical motion, which can be successfully achieved via a wireless flexible wearable electronic device, is essential for people to ensure the appropriate level of exercise. Currently, most of the flexible LC pressure sensors have low sensitivity because of the high Young’s modulus of the dielectric properties (such as PDMS) and the inflexible polymer films (as the substrate of the sensors), which don’t have excellent stretchability to conform to arbitrarily curved and moving surfaces such as joints. In the LC sensing system, the metal rings, as the traditional readout device, are difficult to meet the needs of the portable readout device for the integrated and planar readout antenna. In order to improve the pressure sensitivity of the sensor, the Ecoflex microcolumn used as the dielectric of the capacitive pressure sensor was prepared by using a metal mold copying method. The Ecoflex elastomer substrates enhanced the levels of conformability, which offered improved capabilities to establish intimate contact with the curved and moving surfaces of the skin. The pressure was applied to the sensor by weights, and the resonance frequency curves of the sensor under different pressures were obtained by the readout device connected to the vector network analyzer. The experimental results show that resonant frequency decreases linearly with the increase of applied pressure in a range of 0–23,760 Pa with a high sensitivity of −2.2 MHz/KPa. We designed a coplanar waveguide-fed monopole antenna used to read the information of the LC sensor, which has the potential to be integrated with RF signal processing circuits as a portable readout device and a higher vertical readout distance (up to 4 cm) than the copper ring. The flexible LC pressure sensor can be attached to the skin conformally and is sensitive to limb bending and facial muscle movements. Therefore, it has the potential to be integrated as a body sensor network that can be used to monitor physical motion.