A Dual-Function Sensor for Highly Sensitive Detection of Flame and Humidity.

Early warning sensors rapidly monitor critical temperatures, humidity, and fires, which are crucial to reduce or avoid natural disasters in complex environments, such as fire or water disasters. Here, a highly sensitive, readable, and dual-functional sensor is designed for a fast-response fire alarm and rapid humidity detection based on sustainable biological films (named MSCG films). The MSCG films are composed of grafted sisal nanofibers (MgC), silk nanofibers, graphene, and citric acid (CA). After crosslinking with CA, MSCG films exhibit good wet strength (i.e., 128.8 MPa) after soaking in 100 °C water, thus confirming that the films would be applicable to a broad temperature range in humid environments. After flame ignition, the MSCG films are rapidly carbonized to activate an alarm sound and a light in the circuit with a fire response time as short as 1 s. It exhibits ultrafast temperature response/recovery time (i.e., 0.1 s/0.3 s) and rapid humidity response time (i.e., 0.9 s). The dual-functional sensor is further assembled into a versatile sensor system for real-time monitoring of fire accidents and environmental humidity, which can be integrated into consumer electronics, such as portable laptops and mobile phones.

A High-Wet-Strength Biofilm for Readable and Highly Sensitive Humidity Sensors.

Low-cost and flexible biofilm humidity sensors with good wet strength are crucial for humidity detection. However, it remains a great challenge to integrate good reversibility, rapid humidity response, and robust humid mechanical strength in one sensor. In this respect, we report a facile method to prepare a sustainable biofilm (named MC film) from sisal cellulose microcrystals (MSF-g-COOH) and citric acid (CA). After cross-linking with CA, the MC film exhibits excellent wet strength and rapid humidity response. More importantly, MC film can be used over a wide temperature range with excellent durability and reversibility for humidity detection. A highly sensitive humidity sensor fabricated from the MC film exhibits high reversibility and excellent water resistance and can be applied in humidity and personalized breath health monitoring. Our work fills the gap between biomaterial design and high-performance sensing devices.

A Hydrophobic Sisal Cellulose Microcrystal Film for Fire Alarm Sensors.

At present, environmentally friendly biobased flexible films are of particular interest as next-generation fireproof packaging and sensor materials. To reduce the moisture uptake and fire risks induced by hygroscopic and flammable biobased films, we report a simple and green approach to develop a hydrophobic, flame-retardant composite film with synergetic benefit from soy protein isolate (SPI), sisal cellulose microcrystals (MSF-g-COOH), graphene nanosheets (GN), and citric acid (CA). Compared with SPI/MSF-g-COOH composite films, the as-prepared SPI/MSF-g-COOH/CA/GN composite films have significantly improved water resistance and can maintain excellent physical structure and good electrical conductivity in an ethanol flame. This work opens a pathway for the development of novel fire-retardant fire alarm biosensors.

Tremella polysaccharide-based conductive hydrogel with anti-freezing and self-healing ability for motion monitoring and intelligent interaction.

The application of conductive hydrogels in flexible wearable devices has garnered significant attention. In this study, a self-healing, anti-freezing, and fire-resistant hydrogel strain sensor is successfully synthesized by incorporating sustainable natural biological materials, viz. Tremella polysaccharide and silk fiber, into a polyvinyl alcohol matrix with borax cross-linking. The resulting hydrogel exhibits excellent transparency, thermoplasticity, and remarkable mechanical properties, including a notable elongation (1107.3 %) and high self-healing rate (91.11 %) within 5 min, attributed to the dynamic cross-linking effect of hydrogen bonds and borax. A strain sensor based on the prepared hydrogel sensor can be used to accurately monitor diverse human movements, while maintaining exceptional sensing stability and durability under repeated strain cycles. Additionally, a hydrogel touch component is designed that can successfully interact with intelligent electronic devices, encompassing functions like clicking, writing, and drawing. These inherent advantages make the prepared hydrogel a promising candidate for applications in human health monitoring and intelligent electronic device interaction.

Multi-functional bio-film based on sisal cellulose nanofibres and carboxymethyl chitosan with flame retardancy, water resistance, and self-cleaning for fire alarm sensors.

Flexible and environmentally friendly bio-based films have attracted significant attention as next-generation fire-responsive sensors. However, the low structural stability, durability, and flame retardancy of pure bio-based films limit their application in outdoor and extreme environments. Here, we report the design of a sustainable bio-based composite film assembled from carboxymethyl-modified sisal fibre microcrystals (C-MSF), carboxymethyl chitosan (CMC), graphene nanosheets (GNs), phytic acid (PA), and trivalent iron ions (Fe3+). Cross-linking between Fe3+ and the C-MSF/CMC matrix and the formation of PA-Fe3+ complexes on the surface of the film imparted excellent mechanical properties, chemical stability, self-cleaning ability, and flame retardancy to the bio-film. Furthermore, the bio-film produced a reversible and sensitive response to temperature at 55.3-214.1 °C, and a fire alarm system made from the bio-film had a fire-response time of 4.6 s. In addition, the char layer of the bio-film retained a stable cyclic response to temperature, enabling it to serve as a fire resurgence sensor with a response time of 2.3 s and recovery time of 11.2 s. This work provides a simple pathway for the fabrication of self-cleaning, flame retardant, and water-resistant bio-films that can be assembled into fire alarm systems for the real-time monitoring of fire accidents and resurgence.

Multifunctional bio-films based on silk nanofibres/peach gum polysaccharide for highly sensitive temperature, flame, and water detection.

Given their environment friendliness, light weight, and availability, bio-films have attracted wide interest for various applications in sensor materials. However, obtaining sensors with good environmental stability, excellent flame retardancy, and high wet strength remains a challenge. Herein, we prepared sensitive water, temperature and flame-responsive multi-function bio-films (named as PSCG bio-films) by combining peach gum polysaccharide, silk nanofibres, citric acid, and graphene. The PSCG bio-films demonstrated good flexibility, rapid and consistent water absorption, and stable wet strength at different temperatures. The bio-films showed excellent water sensitivity and rapid fire responsiveness within a short time frame (2 s); moreover, the response and recovery times of the bio-films in the temperature range of 50-150 °C were 0.1 and 0.3 s, respectively. In addition, the bio-films can be applied to micro-sized fire early warning devices and personalized breath monitoring. Our work presents a facile and green approach (without toxic solvent) to fabricate multi-function sensors with applications in various industries.

A stretchable, self-healing, okra polysaccharide-based hydrogel for fast-response and ultra-sensitive strain sensors.

Self-healing conductive hydrogels have attracted widespread attention as a new generation of smart wearable devices and human motion monitoring sensors. To improve the biocompatibility and degradability of such strain sensors, we report a sensor with a sandwich structure based on a biomucopolysaccharide hydrogel. The sensor was constructed with a stretchable self-healing hydrogel composed of polyvinyl alcohol (PVA), okra polysaccharide (OP), borax, and a conductive layer of silver nanowires. The obtained OP/PVA/borax hydrogel exhibited excellent stretchability (~1073.7%) and self-healing ability (93.6% within 5 min), and the resultant hydrogel-based strain sensor demonstrated high sensitivity (gauge factor = 6.34), short response time (~20 ms), and good working stability. This study provides innovative ideas for the development of biopolysaccharide hydrogels for applications in the field of sensors.

Tailoring Thermal Transport Properties of Graphene Paper by Structural Engineering.

As a two-dimensional material, graphene has attracted increasing attention as heat dissipation material owing to its excellent thermal transport property. In this work, we fabricated sisal nanocrystalline cellulose/functionalized graphene papers (NPGs) with high thermal conductivity by vacuum-assisted self-assembly method. The papers exhibit in-plane thermal conductivity as high as 21.05 W m-1 K-1 with a thermal conductivity enhancement of 403% from the pure cellulose paper. The good thermal transport properties of NPGs are attributed to the strong hydrogen-bonding interaction between nanocrystalline cellulose and functionalized graphene and the well alignment structure of NPGs.