Over the past decade, the demand for high-performance wearable sensors has increased because of their capability for interaction with humans. Such sensors have typically been prepared on conventional substrates, such as silicon, PDMS, and copper mesh. In this work, we propose a class of wearable sensors fabricated from reduced graphene oxide (rGO) patterned paper substrates (rGO-paper). These rGO-paper sensors are highly sensitive to various deformations and capable of measuring bending and folding angles as small as 0.2° and 0.1°, respectively. We have demonstrated the applicability of these high-performance rGO-paper sensors by patterning rGO on kirigamis that can detect pulse and the motion of knees, wrists, and fingers. Finally, paper rings lined with rGO sensors were used to control a robotic hand, and an rGO-paper keyboard was used to light LEDs.
Research background of the field:
Conventional metal and semiconductor-based strain sensors cannot fulfil these requirements because of their limited flexibility and sensitivity. To address the above issues and attain the required performance for an ideal flexible strain sensor, many researchers have investigated the use of various nanomaterials, such as nanowires, nanoparticles, carbon nanotubes and graphenes. Among them, graphene, graphene-metal nanowire hybrids, graphene foam and graphene on woven copper mesh have been intensively studied because of their superior flexibility, high conductivity and robust mechanical strength. However, the fabrication processes for these devices require either expensive chemical vapour deposition (CVD), harmful etching, complicated mixing processes, or a combination of these factors. Herein, we have presented a novel and facile approach for developing bendable and foldable strain sensors based on paper substrates patterned with reduced graphene oxide (rGO-paper) that allow full-range operation of wearable electronics. On the one hand, rGO-paper sensors maintain the simplicity of paper-based devices; on the other hand, these devices are inexpensive, scalable and highly sensitive to tiny deflections over a broad sensing range.
Novelty of rGO-paper strain sensors:
Inexpensive paper-based devices have generated considerable interest because these devices are ubiquitous, light in weight, portable, flexible, foldable and biodegradable. Whereas previous studies on paper-based devices have focused on labs-on-a-chip, supercapacitors, actuators, and transistors, no significant attempt has been made to develop wearable paper electronics before our work. We have demonstrated the use of rGO-paper sensors as wearable devices for detecting human body moments and controlling robotic hands. Furthermore, highly sensitive rGO-paper sensors were used to develop a paper-based keyboard.
Compared with conventional graphene/GO patterning approaches, our proposed method not only is simple, rapid and straightforward but also allows freedom in the choice of creative and delicate designs. The key advantage of our rGO-paper sensor fabrication process is that it supports sensor production in remote locations with limited laboratory facilities.
The rGO-paper sensors possess excellent bending and folding sensitivity over a wide detection range from 0 to ± 180° with detection limits of 0.2° and 0.1° for the bending and folding angles, respectively. The rGO-paper sensors provide a stable change in conductance during initial bending/folding cycles and allow us to plan for a low-cost and use-and-through paper-based sensor, which open a new door of biodegradable electronics.
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