High-range noise immune supersensitive graphene-electrolyte capacitive strain sensor for biomedical applications

Machine Learning-Enabled Environmentally Adaptable Skin-Electronic Sensor for Human Gesture Recognition

Stretchable sensors have been widely investigated and developed for the purpose of human motion detection, touch sensors, and healthcare monitoring, typically converting mechanical/structural deformation into electrical signals. The viscoelastic strain of stretchable materials often results in nonlinear stress-strain characteristics over a broad range of strains, consequently making the stretchable sensors at the body joints less accurate in predicting and recognizing human gestures. Accurate recognition of human gestures can be further deteriorated by environmental changes such as temperature and humidity. Here, we demonstrated an environment-adaptable high stress-strain linearity (up to ε = 150%) and high-durability (>100,000 cycles) stretchable sensor conformally laminated onto the body joints for human gesture recognition. The serpentine configuration of our ionic liquid-based stretchable film enabled us to construct broad data sets of mechanical strain and temperature changes for machine learning-based gesture recognition. Signal recognition and training of distinct strains and environmental stimuli using a machine learning-based algorithm analysis successfully measured and predicted the joint motion in a temperature-changing environment with an accuracy of 92.86% (R-squared). Therefore, we believe that our serpentine-shaped ion gel-based stretchable sensor harmonized with machine-learning analysis will be a significant achievement toward environmentally adaptive and multianalyte sensing applications. Our proposed machine learning-enabled multisensor system may enable the development of future electronic devices such as wearable electronics, soft robotics, electronic skin, and human-machine interaction systems.

Graphene-based strain sensor with sandwich structure and its application in bowel sounds monitoring

Surgery is one of the primary treatment modalities for gastrointestinal tumors but can lead to postoperative ileus (POI), which can aggravate pain and increase costs. The incidence of POI can be effectively reduced by monitoring bowel sounds to assist doctors in deciding the timing of transoral feeding. In this study, we prepared a flexible strain sensor based on a graphene composite material and tested the feasibility of sensor monitoring of bowel sounds using simultaneous stethoscope and sensor monitoring. We found that the time of hearing the bowel sounds (12.0–12.1 s) corresponded to the time of waveform change monitored by the sensor (12.036 s), and the sound tone magnitude corresponded to the waveform amplitude. This proves that the application of sensors to monitor bowel sounds is feasible, which opens up a new field for the application of graphene sensors and provides a new way for clinicians to judge the condition of the intestine.

Combining medicine and materials science. First application of graphene strain sensors for monitoring bowel sounds

Multifunctional Graphene Sensor Ensemble as a Smart Biomonitoring Fashion Accessory

Biomonitoring wearable sensors based on two-dimensional nanomaterials have recently elicited keen research interest and potential for a new range of flexible nanoelectronic devices. Practical nanomaterial-based devices suited for real-world service, which exhibit first-rate performance while being an attractive accessory, are still distant. We report a multifunctional flexible wearable sensor fabricated using an ultrathin percolative layer of graphene nanosheets on laser-patterned gold circular interdigitated electrodes for monitoring vital human physiological parameters. This graphene on laser-patterned electrode (GLE) sensor displays an excellent strain resolution of 245 με (0.024%) and a record high gauge factor of 6.3 × 10⁷, with exceptional stability and repeatability in its operating range. The sensor was tested for human physiological monitoring like measurement of heart rate, breathing rate, body temperature, and hydration level, which are vital health parameters, especially considering the current pandemic scenario. The sensor also served in applications such as a pedometer, limb movement tracker, and control switch for human interaction. The innovative laser-etch process used to pattern gold thin-film electrodes, with the multifunctional incognizable graphene layer, provides a technique for integrating multiple sensors in a wearable band. The reported work marks a giant leap from the conventional banal devices to a highly marketable multifunctional sensor array as a biomonitoring fashion accessory.

Flexible strain sensor with high sensitivity, fast response, and good sensing range for wearable applications

Flexible strain sensors are emerging rapidly and overcoming the drawbacks of traditional strain sensors. However, many flexible sensors failed to balance the sensitivity, response time, and the desired sensing range. This work proposes a novel and cost-effective strain sensor which simultaneously achieved high sensitivity, fast response, and a good sensing range. It illustrates a prototype strain sensor realized with a nanocomposite constituting reduced graphene oxide and palladium as the primary sensing elements. These sensors were fabricated with manual screen-printing technology. The sensor exhibited an outstanding performance for the different strains ranging from 0.1% to 45%. As a result, a substantially high gauge factor around 1523 at a strain of as high as 45% and a rapid response time of 47 ms was obtained. This work demonstrated potential applications like real-time monitoring of pulse and respiration, and other physical movement detection, which become crucial parameters to be measured continuously during the COVID-19 pandemic.

Application of Graphene as a Nanoindenter Interacting with Phospholipid Membranes-Computer Simulation Study

Synthesis of graphene (GN) in 2004 stimulated wide interest in potential applications of 2D materials in catalysis, optoelectronics, biotechnology, and construction of sensing devices. In the presented study, interactions between GN sheets and phospholipid bilayers are examined using steered molecular dynamics simulations. GN sheets of different sizes were inserted into a bilayer and subsequently withdrawn from it at two different rates (1 and 2 m/s). In some cases, nanoindentation led to substantial damage of the phospholipid bilayer; however, an effective self-sealing process occurred even after significant degradation. The average force and work, deflection of the membrane during indentation, withdrawal processes, and structural changes caused by moving sheets are discussed. These quantities are utilized to estimate the suitability of GN sheets for targeted drug delivery or other nanomedicine tools. The results are compared with those obtained for other nanostructures such as homogeneous and heterogeneous nanotubes.

Stretchable respiration sensors: Advanced designs and multifunctional platforms for wearable physiological monitoring

Respiration signals are a vital sign of life. Monitoring human breath provides critical information for health assessment, diagnosis, and treatment for respiratory diseases such as asthma, chronic bronchitis, and emphysema. Stretchable and wearable respiration sensors have recently attracted considerable interest toward monitoring physiological signals in the era of real time and portable healthcare systems. This review provides a snapshot on the recent development of stretchable sensors and wearable technologies for respiration monitoring. The article offers the fundamental guideline on the sensing mechanisms and design concepts of stretchable sensors for detecting vital breath signals such as temperature, humidity, airflow, stress and strain. A highlight on the recent progress in the integration of variable sensing components outlines feasible pathways towards multifunctional and multimodal sensor platforms. Structural designs of nanomaterials and platforms for stretchable respiration sensors are reviewed.

Electric Spark Induced Instantaneous and Selective Reduction of Graphene Oxide on Textile for Wearable Electronics

Reduced graphene oxide (rGO) attracts great popularity as an alternative to pristine graphene because of the facile synthesis process of its precursor, graphene oxide (GO). Electrical conduction of GO is tunable, subject to the extent of reduction of oxygen functional groups in it. This work for the first time demonstrates rapid reduction of GO using spark at ambient conditions. A stream of spark generated by applying high electric potential across two electrodes, when passed through a film of GO deposited on a porous substrate, reduces it into rGO. Upon sparking, the electrical resistance of the GO film drops down by an order of six within a second, making the reduction process instantaneous. X-ray photoelectron spectroscopy and Raman spectra of spark-reduced graphene oxide (SrGO) films revealed a high C/O ratio with an increase in the domain of sp²-hybridized carbon. The electromechanical properties of SrGO were practically examined by testing it as a flex sensor by incorporating its films with commercially available gloves. It showed high sensitivity for bending and good repeatability while offering an easy route for textile integration, making an impactful statement about the potential of sparking as a cost-effective method to reduce GO on a large scale.