Wearable, Flexible, Disposable Plasma-Reduced Graphene Oxide Stress Sensors for Monitoring Activities in Austere Environments

In austere environments, for example, in outer space, on surfaces of extra-terrestrial bodies (Moon, Mars, etc.), or under water, technologies that can enable continuous, reliable, and authentic monitoring of movement of human operators and devices can be critical. We report here the production and human body test of wearable, flexible graphene oxide stress sensors suitable for real-time monitoring of body parameters, state and position of humans, and automatic equipment. These sensors have excellent sensitivity and signal strength across a wide strain range, alleviating the need for additional instrumentation for signal processing and amplification. Their low cost makes them virtually disposable, which may benefit such applications as smart clothing. The sensors were fabricated by a concomitant reduction and N-doping of graphene oxide on polydimethylsiloxane in N₂-H₂ plasma. The direct bias and other plasma parameters have a significant effect on the reduction and properties of graphene oxide sensors, as shown by optical emission, Raman and X-ray photoelectron spectroscopies, and X-ray diffraction. Optical emission showed different excitation and ionization processes involving atomic and molecular species in the N₂-H₂ discharge. The photoelectron spectroscopy has confirmed the graphene reduction and introduction of nitrogen doping into the reduced graphene oxide. The bias efficiently controls plasma-induced electric fields, and plasma-related effects determine the N-doping levels. The reduced graphene oxides demonstrate excellent tensile properties, which make them suitable for efficient but cheap stress sensors. This eco-friendly, fast, room-temperature method shows a great potential for fabrication of efficient, flexible sensors.