High Performance Three‐Dimensional Chemical Sensor Platform Using Reduced Graphene Oxide Formed on High Aspect‐Ratio Micro‐Pillars

The sensing performance of chemical sensors can be achieved not only by modification or hybridization of sensing materials but also through new design in device geometry. The performance of a chemical sensing device can be enhenced from a simple three‐dimensional (3D) chemiresistor‐based gas sensor platform with an increased surface area by forming networked, self‐assembled reduced graphene oxide (R‐GO) nanosheets on 3D SU8 micro‐pillar arrays. The 3D R‐GO sensor is highly responsive to low concentration of ammonia (NH₃) and nitrogen dioxide (NO₂) diluted in dry air at room temperature. Compared to the two‐dimensional planar R‐GO sensor structure, as the result of the increase in sensing area and interaction cross‐section of R‐GO on the same device area, the 3D R‐GO gas sensors show improved sensing performance with faster response (about 2%/s exposure), higher sensitivity, and even a possibly lower limit of detection towards NH₃ at room temperature.     

Free‐Standing Functionalized Graphene Oxide Solid Electrolytes in Electrochemical Gas Sensors

A free‐standing sulfonic acid functionalized graphene oxide (fSGO)‐based electrolyte film is prepared and used in an electrochemical gas sensor, an alcohol fuel cell sensor (AFCS), for the detection of alcohol. The fSGO electrolyte film‐based AFCS detects ethanol vapor with excellent response, linearity, and sensitivity, since it possesses a high proton conductivity (58 mS cm^?1 at 55 °C). An ethanol detection limit level as low as 25 ppm is achieved and high selectivity for ethanol over acetone is demonstrated. These results do not only show the promising potential of fSGO films in an electrochemical gas sensors, specifically a portable breathalyzer, but also open an alternative pathway to investigate the application of graphene derivatives in the field of gas sensors.     

Flexible Transparent Reduced Graphene Oxide Sensor Coupled with Organic Dye Molecules for Rapid Dual‐Mode Ammonia Gas Detection

Flexible chemical sensors utilizing chemically sensitive nanomaterials are of great interest for wearable sensing applications. However, obtaining high performance flexible chemical sensors with high sensitivity, fast response, transparency, stability, and workability at ambient conditions is still challenging. Herein, a newly designed flexible and transparent chemical sensor of reduced graphene oxide (R‐GO) coupled with organic dye molecules (bromophenol blue) is introduced. This device has promising properties such as high mechanical flexibility (>5000 bending cycles with a bending radius of 0.95 cm) and optical transparency (>60% in the visible region). Furthermore, stacking the water‐trapping dye layer on R‐GO enables a higher response as well as workability in a large relative humidity range (up to 80%), and dual‐mode detection capabilities of colorimetric and electrical sensing for NH₃ gas (5–40 ppm). These advantageous attributes of the flexible and transparent R‐GO sensor coupled with organic dye molecules provide great potential for real‐time monitoring of toxic gas/vapor in future practical chemical sensing at room conditions in wearable electronics.     

A Flexible Reduced Graphene Oxide Field‐Effect Transistor for Ultrasensitive Strain Sensing

A new kind of flexible strain sensor based on a reduced graphene oxide field‐effect transistor (rGO FET) with ultrasensitivity, stability, and repeatability for the detection of tensile and compressive strains is demonstrated. The novelty of the rGO FET strain sensor is the incorporation of a rGO channel as a sensing layer in which the electrical resistance can be greatly modified upon application of an extremely low level of strain resulting in an intrinsically amplified sensing signal. The rGO FET device is ultrasensitive to extremely low strain levels, as low as 0.02%. Due to weak coupling between adjacent nanosheets, therefore, upon applying small levels of strain into the rGO thin film, a modulation of the internanosheet resistance (R_inter) is expected, inducing a large change in the transconductance of the rGO FET. Using a simple printing and self‐assembly process, the facile fabrication of an rGO FET array over a large area is also demonstrated. In addition, the device can detect small and rapid physical movements of the human body.