Though
the widely available, low-cost, and disposable papers have
been explored in flexible paper-based pressure sensors, it is still
difficult for them to simultaneously achieve ultrahigh sensitivity,
low limit and broad range of detection, and high-pressure resolution.
Herein, we demonstrate a novel flexible paper-based pressure sensing
platform that features the MXene-coated tissue paper (MTP) sandwiched
between a polyimide encapsulation layer and a printing paper with
interdigital electrodes. After replacing the polyimide with weighing
paper in the MTP pressure sensor, the silver interdigital electrodes
can be recycled through incineration. The resulting pressure sensor
with polyimide or paper encapsulation exhibits a high sensitivity
of 509.5 or 344.0 kPa–1, a low limit (∼1
Pa) and a broad range (100 kPa) of detection, and outstanding stability
over 10 000 loading/unloading cycles. With ultrahigh sensitivity
over a wide pressure range, the flexible pressure sensor can monitor
various physiological signals and human movements. Configuring the
pressure sensors into an array layout results in a smart artificial
electronic skin to recognize the spatial pressure distribution. The
flexible pressure sensor can also be integrated with signal processing
and wireless communication modules on a face mask as a remote respiration
monitoring system to wirelessly detect various respiration conditions
and respiratory abnormalities for early self-identification of opioid
overdose, pulmonary fibrosis, and other cardiopulmonary diseases.
The accurate, continuous analysis of healthcare-relevant gases such as nitrogen oxides (NOx) in a humid environment remains elusive for low-cost, stretchable gas sensing devices. This study presents the design and demonstration of a moisture-resistant, stretchable NOx gas sensor based on laser-induced graphene (LIG). Sandwiched between a soft elastomeric substrate and a moisture-resistant semipermeable encapsulant, the LIG sensing and electrode layer is first optimized by tuning laser processing parameters such as power, image density, and defocus distance. The gas sensor, using a needlelike LIG prepared with optimal laser processing parameters, exhibits a large response of 4.18‰ ppm−1 to NO and 6.66‰ ppm−1 to NO2, an ultralow detection limit of 8.3 ppb to NO and 4.0 ppb to NO2, fast response/recovery, and excellent selectivity. The design of a stretchable serpentine structure in the LIG electrode and strain isolation from the stiff island allows the gas sensor to be stretched by 30%. Combined with a moisture-resistant property against a relative humidity of 90%, the reported gas sensor has further been demonstrated to monitor the personal local environment during different times of the day and analyze human breath samples to classify patients with respiratory diseases from healthy volunteers. Moisture-resistant, stretchable NOx gas sensors can expand the capability of wearable devices to detect biomarkers from humans and exposed environments for early disease diagnostics.
The surge in air pollution and respiratory diseases across the globe has spurred significant interest in the development of flexible gas sensors prepared by low-cost and scalable fabrication methods. However, the limited breathability in the commonly used substrate materials reduces the exchange of air and moisture to result in irritation and a low level of comfort. This study presents the design and demonstration of a breathable, flexible, and highly sensitive NO2 gas sensor based on the silver (Ag) decorated laser-induced graphene (LIG) foam. The scalable laser direct writing transforms the self-assembled block copolymer and resin mixture with different mass ratios into highly porous LIG with varying pore sizes. Decoration of Ag nanoparticles on the porous LIG further increases the specific surface area and conductivity to result in a highly sensitive and selective composite to detect nitrogen oxides. The as-fabricated Ag/LIG gas sensor on a flexible polyethylene substrate exhibits a large response of -12‰, fast response/recovery of 40/291 s, a low detection limit of a few ppb at room temperature. Integrating the Ag/LIG composite on diver fabric substrates further results in breathable gas sensors and intelligent clothing, which allows permeation of air and moisture to provide long-term practical use with an improved level of comfort.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.