Pencil-on-Paper Humidity Sensor Treated with NaCl Solution for Health Monitoring and Skin Characterization

Abstract

Although flexible humidity sensors are essential for human health monitoring, it is still challenging to achieve high sensitivity and easy disposal with simple, low-cost fabrication processes. This study presents the design and fabrication of highly reliable hand-drawn interdigital electrodes from pencil-on-paper treated with NaCl solution for highly sensitive hydration sensors working over a wide range of relative humidity (RH) levels from 5.6% to 90%. The applications of the resulting flexible humidity sensor go beyond the monitoring of respiratory rate and proximity to characterizations of human skin types and evaluations of skin barrier functions through insensible sweat measurements. The sensor array can also be integrated with a diaper to result in smart diapers to alert for an early diaper change. The design and fabrication strategies presented in this work could also be leveraged for the development of wearable, self-powered, and recyclable sensors and actuators in the future.

Recent Advances in Biodegradable Green Electronic Materials and Sensor Applications

“…Niu et al fabricated a pencil‐on‐paper humidity sensor using a facile and cost‐effective fabrication process, which was further integrated with smart face masks and diapers for health monitoring (Figure 6c). [ 132 ] Chemical treatment with NaCl increased the number of mobile electrons and improved the ionic conductivity, eventually facilitating vapor absorption. The sensor soaked in NaCl exhibited a highly enhanced signal‐to‐noise ratio (SNR) of 1573‐fold between the treated and untreated sensors.…”

Stretchable Organohydrogel with Adhesion, Self-Healing, and Environment-Tolerance for Wearable Strain Sensors

“…The overlap of wearable healthcare applications and flexible electronic engineering is guiding the development direction of functional soft materials 1,2 and device design integration. 3,4 Recently, hydrogel-based wearable sensors with high hydration, tunable functionality, and high sensitivity have shone in fields such as medical devices, 5−8 human−machine interfaces, 9−12 and flexible electrodes. 13−16 For example, Fu et al developed a super-stretchable conductive hydrogel based on triple crosslinking for sensitive monitoring of human physiological motions.…”

“…The overlap of wearable healthcare applications and flexible electronic engineering is guiding the development direction of functional soft materials , and device design integration. , Recently, hydrogel-based wearable sensors with high hydration, tunable functionality, and high sensitivity have shone in fields such as medical devices, − human–machine interfaces, − and flexible electrodes. − For example, Fu et al developed a super-stretchable conductive hydrogel based on triple crosslinking for sensitive monitoring of human physiological motions . Nevertheless, due to the lack of adhesion properties, the conventional hydrogel-based strain sensor required additional assistance to achieve close contact between the sensor and the substrate during usage, which largely impair the accuracy and durability of signal detection. − Meanwhile, these hydrogels were easily damaged during the complex and continuous movement of the human body, which limited their application especially in human health care monitoring.…”

Response Regulation for Epidermal Fabric Strain Sensors via Mechanical Strategy

“…Recent advances in flexible electronics have paved the way for a wide variety of important applications, [ 1–4 ] such as low‐power radio communication systems, [ 5 ] efficient energy harvesting/storage devices, [ 6,7 ] human‐machine interaction technologies, [ 8–11 ] miniaturized electronic/optoelectronic components, 12–14] electronic microfliers [ 15 ] and smart electronic skin for robots [ 16 ] and aircraft. [ 17,18 ] At the same time, low‐cost materials and manufacturing methods, [ 19–24 ] fabrication methods to prepare deformable sensors or functional circuits on 3D freeform surfaces, [ 25–29 ] and self‐powered (standalone) stretchable sensing platforms have also been flourishing. [ 30,31 ] Extensive opportunities are created for developing the bio‐integrated flexible electronic devices at intimate biotic/abiotic interfaces [ 32,33 ] for disease treating [ 34 ] and health monitoring [ 35,36 ] purposes, eliminating the inherent mechanic mismatch between soft bio‐tissues and rigid electronic components.…”