Skin-Inspired All-Natural Biogel for Bioadhesive Interface.

Natural material-based hydrogels are considered ideal candidates for constructing robust bio-interfaces due to their environmentally sustainable nature and biocompatibility. However, these hydrogels often encounter limitations such as weak mechanical strength, low water resistance, and poor ionic conductivity. Here, inspired by the role of natural moisturizing factor (NMF) in skin, a straightforward yet versatile strategy is proposed for fabricating all-natural ionic biogels that exhibit high resilience, ionic conductivity, resistance to dehydration, and complete degradability, without necessitating any chemical modification. A well-balanced combination of gelatin and sodium pyrrolidone carboxylic acid (an NMF compound) gives rise to a significant enhancement in the mechanical strength, ionic conductivity, and water retention capacity of the biogel compared to pure gelatin hydrogel. The biogel manifests temperature-controlled reversible fluid-gel transition properties attributed to the triple-helix junctions of gelatin, which enables in situ gelation on diverse substrates, thereby ensuring conformal contact and dynamic compliance with curved surfaces. Due to its salutary properties, the biogel can serve as an effective and biocompatible interface for high-quality and long-term electrophysiological signal recording. These findings provide a general and scalable approach for designing natural material-based hydrogels with tailored functionalities to meet diverse application needs.

In-Time Detection of Plant Water Status Change by Self-Adhesive, Water-Proof, and Gas-Permeable Electrodes.

Leaf capacitance can reflect plant water content. However, the rigid electrodes used in leaf capacitance monitoring may affect plant health status. Herein, we report a self-adhesive, water-proof, and gas-permeable electrode fabricated by in situ electrospinning of a polylactic acid nanofiber membrane (PLANFM) on a leaf, spraying a layer of the carbon nanotube membrane (CNTM) on PLANFM, and in situ electrospinning of PLANFM on CNTM. The electrodes could be self-adhered to the leaf via electrostatic adhesion due to the charges on PLANFM and the leaf, thus forming a capacitance sensor. Compared with the electrode fabricated by a transferring approach, the in situ fabricated one did not show obvious influence on plant physiological parameters. On that basis, a wireless leaf capacitance sensing system was developed, and the change of plant water status was detected in the first day of drought stress, which was much earlier than direct observation of the plant appearance. This work paved a useful way to realize noninvasive and real-time detection of stress using plant wearable electronics.

Bilayer Wood Membrane with Aligned Ion Nanochannels for Spontaneous Moist-Electric Generation.

Water-enabled electricity generation (WEG) technologies are considered to be an attractive and renewable approach to meet energy crisis and environmental pollution globally. However, the existing WEG technologies still face tremendous challenges including high material cost, harmful components, and specific environmental requirements. Herein, a high-performance wood-based moisture-enabled electric generator (WMEG) is fabricated. Natural wood is cut perpendicular to the tree growth direction and engineered by simple chemical modification. The obtained bilayer wood membrane has robust mechanical framework with aligned ion nanochannels, abundant dissociated functional groups, and spontaneous water adsorption in the air. At the relative humidity of 85%, one WMEG can generate a voltage of 0.57 V. The device can also effectively sense biological water information as a self-powered sensor. The biophile design contributes a practical moist-electric generation strategy that offers clean energy, especially for undeveloped and disaster-relief regions where electricity is limited by high cost or crippled power facilities.

Sustainable Natural Bio-Origin Materials for Future Flexible Devices.

Flexible devices serve as important intelligent interfaces in various applications involving health monitoring, biomedical therapies, and human-machine interfacing. To address the concern of electronic waste caused by the increasing usage of electronic devices based on synthetic polymers, bio-origin materials that possess environmental benignity as well as sustainability offer new opportunities for constructing flexible electronic devices with higher safety and environmental adaptivity. Herein, the bio-source and unique molecular structures of various types of natural bio-origin materials are briefly introduced. Their properties and processing technologies are systematically summarized. Then, the recent progress of these materials for constructing emerging intelligent flexible electronic devices including energy harvesters, energy storage devices, and sensors are introduced. Furthermore, the applications of these flexible electronic devices including biomedical implants, artificial e-skin, and environmental monitoring are summarized. Finally, future challenges and prospects for developing high-performance bio-origin material-based flexible devices are discussed. This review aims to provide a comprehensive and systematic summary of the latest advances in the natural bio-origin material-based flexible devices, which is expected to offer inspirations for exploitation of green flexible electronics, bridging the gap in future human-machine-environment interactions.

Breathable Nanogenerators for an On-Plant Self-Powered Sustainable Agriculture System.

Building an intelligent interface between plants and the environment is of paramount importance for real-time monitoring of the health status of plants, especially promising for high agricultural yield. Although the advancement of various sensors allows automated monitoring, developing a sustainable power supply for these electronic devices remains a formidable challenge. Herein, a waterproof and breathable triboelectric nanogenerator (WB-TENG) is designed based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanofibers embedded with fluorinated carbon nanotubes (F-CNT) microspheres, which was realized by simultaneous electrospinning and electrospraying, respectively. Using carbon nanotubes (CNT) as the electrode, the WB-TENG shows micro-to-nano hierarchical porous structures and high electrostatic adhesion, exhibiting a high output power density of 330.6 µW cm-2, breathability, and hydrophobicity. Besides, the WB-TENG can be conformally self-attached to plant leaves without sacrificing the intrinsic physiological activities of plants, capable of harvesting typical environmental energy from wind and raindrops. Results demonstrate that the WB-TENG can serve as a sustainable power supply for a wireless plant sensor, enabling real-time monitoring of the health status of plants. This work realizes the concept of constructing a plant compatible TENG with environment adaptivity and energy scavenging ability, showing great potential in building a self-powered agriculture system.

One-step and large-scale fabrication of flexible and wearable humidity sensor based on laser-induced graphene for real-time tracking of plant transpiration at bio-interface.

The rapidly growing demand for humidity sensing in various applications such as noninvasive epidermal sensing, water status tracking of plants, and environmental monitoring has triggered the development of high-performance humidity sensors. In particular, timely communication with plants to understand their physiological status may facilitate preventing negative influence of environmental stress and enhancing agricultural output. In addition, precise humidity sensing at bio-interface requires the sensor to be both flexible and stable. However, challenges still exist for the realization of efficient and large-scale production of flexible humidity sensors for bio-interface applications. Here, a convenient, effective, and robust method for massive production of flexible and wearable humidity sensor is proposed, using laser direct writing technology to produce laser-induced graphene interdigital electrode (LIG-IDE). Compared to previous methods, this strategy abandons the complicated and costly procedures for traditional IDE preparation. Using graphene oxide (GO) as the humidity-sensitive material, a flexible capacitive-type GO-based humidity sensor with low hysteresis, high sensitivity (3215.25 pF/% RH), and long-term stability (variation less than ± 1%) is obtained. These superior properties enable the sensor with multifunctional applications such as noncontact humidity sensing and human breath monitoring. In addition, this flexible humidity sensor can be directly attached onto the plant leaves for real-time and long-term tracking transpiration from the stomata, without causing any damage to plants, making it a promising candidate for next-generation electronics for intelligent agriculture.

Alchemy-Inspired Green Paper for Spontaneous Recovery of Noble Metals.

Recycling of noble metal from waste materials, namely from electronic wastes (e-waste), spent catalyst, and industrial wastewater, is attracting growing attention due to the scarcity, economic importance, and criticality of those noble metals. Traditional techniques reported to date require toxic reagent and strict extraction conditions, which deeply hinders the development of precious metal recovery in complex environments. Here, an approach is proposed that uses flexible metallic transition metal dichalcogenide (TMD) paper, which provides abundant active sites for spontaneous adsorption and reduction of noble metal ions, as an Alchemy-inspired template to recover noble metal in an efficient and green way without the aid of reductant and heating. The metallic TMD (MoS2 , WS2 ) paper is shown to rapidly extract five noble metal ions (Au, Pd, Pt, Ag, and Ru) from complex samples containing various interferents. This unique property endows the metallic TMD paper with gifted ability in extracting gold from e-waste, and recovering platinum group metals (palladium and platinum) from spent catalysts, which provides a blueprint for the design of next-generation green platforms for noble metal regeneration.

One-Step and Spontaneous in Situ Growth of Popcorn-like Nanostructures on Stretchable Double-Twisted Fiber for Ultrasensitive Textile Pressure Sensor.

Highly conductive fibers play an essential role in the development of electronic textiles for wearable devices. Even though great progress has been made recently, big challenges of developing simple and rapid methods to prepare functional fibers with stretchability, high sustainability, and electrical conductivity still remain. Herein, we proposed a simple, rapid, and scalable approach to fabricate stretchable and conductive fibers by growing Au nanostructures on a double-twisted fiber coated with metallic MoS2 nanosheets. The formation of Au nanostructures with a unique "popcorn"-like shape (namely, Au "nanopopcorn", AuNPC) occurs instantaneously and spontaneously on the surface of MoS2-coated fiber, without any additional reducing reagents or heating conditions. Moreover, the overall fabrication process takes less than 5 min, demonstrating the realization of fast fabrication of functional conductive fibers. The obtained fiber with piezoresistive property can be fabricated into a pressure sensor. The unique morphology of AuNPC with a rough surface can significantly enhance the performance of the pressure sensor, with high sensitivity of up to 0.19 kPa-1 and a fast response time of 93 ms. Furthermore, the functional fiber can be woven into electronic textiles with sensing arrays, which has multiple two-dimensional (2D) force mapping properties. Therefore, we envision that this simple, rapid, and scalable method to fabricate conductive functional fibers would show great potential in the field of electronic textiles and wearable devices.

Spontaneous growth and regulation of noble metal nanoparticles on flexible biomimetic MXene paper for bioelectronics.

Smart and green construction of noble metal nanostructures on two-dimensional nanomaterials-based flexible paper-like materials have gained extensive attention due to the formed hybrid papers have shown great promise in the applications of energy devices, sensing electronics, actuators, and chemical filters. Herein, a cost-effective and environment-friendly strategy to realize the spontaneous growth of noble metal nanoparticles (Au, Pd, and Pt) on flexible biomimetic MXene paper was proposed. The self-defined regulation of formed noble metal nanoparticles could be easily achieved, and the bimetallic (AuPt, PdPt) nanoparticles decorated MXene paper could be obtained at the mean time. These findings bring a simple, efficient and green way for constructing various hybrid MXene paper with outperforming electrocatalytic activities, which was demonstrated by the sensitive detection of superoxide (O2•-) and the good stability and reproducibility after a long-term usage. The outstanding analytical performance of the obtained AuPtNPs/MXene paper in O2•- monitoring leads to a satisfactory application in real-time extracellular biosensing. The investigation for spontaneous growth and regulation of noble metal nanoparticles on flexible biomimetic MXene paper exhibits a huge application potential for constructing high-performance flexible bioelectronics and energy-related devices.

Phase-Dependent Fluorescence Quenching Efficiency of MoS2 Nanosheets and Their Applications in Multiplex Target Biosensing.

Two-dimensional layered transition-metal dichalcogenide nanosheets have shown great potential in biosensors owing to their unique properties. Here, we exfoliated ultrathin metallic and semiconductive MoS2 nanosheets based on a chemical exfoliation method. We compared the difference of fluorescence quenching efficiency between metallic and semiconductive MoS2 nanosheets. We found that the fluorescence quenching efficiency of MoS2 nanosheets is phase-dependent. The ultrathin metallic MoS2 nanosheets with larger contents of a 1T-phase structure show higher fluorescence quenching efficiency than semiconductive MoS2 nanosheets, which can be ascribed to the higher conductivity of metallic MoS2 nanosheets. On the basis of the excellent fluorescence quenching efficiency of metallic MoS2 nanosheets and their discriminative adsorption toward single-strand DNA and double-strand DNA, a fluorescent biosensor for multiplex detection of DNA was developed. This fluorescent biosensing platform allows simultaneous fluorescence quenching of two single-strand DNA probes labeled with different fluorophores, resulting in multiplex detection of different DNA sequences in one homogeneous solution with high sensitivity.

Metallic Transition Metal Dichalcogenide Nanosheets as an Effective and Biocompatible Transducer for Electrochemical Detection of Pesticide.

Owing to their large specific surface, favorable electrical conductivity, and excellent electrocatalytic capabilities, two-dimensional transition metal dichalcogenides have received considerable attention in the field of biosensors. On the basis of these properties, we developed a portable and disposable enzyme-based biosensor for paraoxon detection using a metallic MoS2 nanosheets modified screen-printed electrode (SPE). The exfoliated ultrathin metallic MoS2 nanosheets can accelerate the electron transfer on electrode surface and contribute to the immobilization of acetylcholinesterase (AChE) via the cross-linking of glutaraldehyde. Electrodeposited gold nanoparticles (AuNPs) on SPE were used to immobilize MoS2 nanosheets through the interaction between Au atoms on AuNPs and S atoms on MoS2. Using acetylcholine as the substrate, AChE can catalyze the formation of electroactive thiocholine and further generate the redox current. In the presence of paraoxon, the activity of AChE can be inhibited, making the related electrochemical signals weaken. Under the optimized conditions, this electrochemical biosensor exhibited a favorable linear relationship with the concentration of paraoxon from 1.0 to 1000 µg L-1, with the detection limit of 0.013 µg L-1. Furthermore, this developed biosensor was successfully applied to detect paraoxon in pretreated apple and pakchoi samples, which can provide a reliable method for the rapid analysis of organophosphorus pesticides in agricultural products.

Recent Progress in Nanomaterial-Based Optical Aptamer Assay for the Detection of Food Chemical Contaminants.

Food chemical contaminants are a major factor in the cause of foodborne diseases and can do harm to human health. Hence, it is highly desirable to develop robust, easy, and sensitive methods for rapid evaluation of food chemical contaminants. Nanomaterial-based optical aptasensors combined with the advantages of the high selectivity of optical detection techniques, excellent stability of aptamer, and the unique properties of nanomaterials have been recognized as useful tools for routine biosensing applications. The recent progress in nanomaterial-based optical aptamer assays to determine food chemical contaminants including heavy metals, toxins, pesticides, and antibiotics are presented in this paper. Furthermore, the major challenges and future prospects in this field are discussed to provide ideas for further research.

Recent advances in nanomaterial-based biosensors for antibiotics detection.

Antibiotics are able to be accumulated in human body by food chain and may induce severe influence to human health and safety. Hence, the development of sensitive and simple methods for rapid evaluation of antibiotic levels is highly desirable. Nanomaterials with excellent electronic, optical, mechanical, and thermal properties have been recognized as one of the most promising materials for opening new gates in the development of next-generation biosensors. This review highlights the current advances in the nanomaterial-based biosensors for antibiotics detection. Different kinds of nanomaterials including carbon nanomaterials, metal nanomaterials, magnetic nanoparticles, up-conversion nanoparticles, and quantum dots have been applied to the construction of biosensors with two main signal-transducing mechanisms, i.e. optical and electrochemical. Furthermore, the current challenges and future prospects in this field are also included to provide an overview for future research directions.