Rapid and In-Field Sensing of Hydrogen Peroxide in Plant by Hydrogel Microneedle Patch.

The rapidly changing climate is exacerbating the environmental stress that negatively impacts crop health and yield. Timely sensing of plant response to stress is beneficial to timely adjust planting conditions, promoting the healthy growth of plants, and improving plant productivity. Hydrogen peroxide (H2O2) is an important molecule of signal transduction in plants. However, the common methods for detecting H2O2  in plants are associated with certain drawbacks, such as long extraction time, cumbersome steps, dependence on large instruments, and difficulty in realizing in-field sensing. Therefore, it is urgent to establish more efficient detection methods to realize the rapid detection of H2O2 content in plants. In this research, poly (methyl vinyl ether-alt-maleic acid) (PMVE/MA) hydrogel microneedle (MN) patch for rapid extraction of leaf sap are prepared, and the extraction mechanism of PEG-crosslinked PMVE/MA hydrogel MN patch is studied. A method of rapid detection of H2O2 content in plants based on MN patch with optical detection technology is constructed. The hydrogel MN patch can be used for timely H2O2 analysis. This application enables new opportunities in plant engineering, and can be extended to the safety and health monitoring of other plants and animals.

Extrusion Printing of Surface-Functionalized Metal-Organic Framework Inks for a High-Performance Wearable Volatile Organic Compound Sensor.

Wearable sensors hold immense potential for real-time and non-destructive sensing of volatile organic compounds (VOCs), requiring both efficient sensing performance and robust mechanical properties. However, conventional colorimetric sensor arrays, acting as artificial olfactory systems for highly selective VOC profiling, often fail to meet these requirements simultaneously. Here, a high-performance wearable sensor array for VOC visual detection is proposed by extrusion printing of hybrid inks containing surface-functionalized sensing materials. Surface-modified hydrophobic polydimethylsiloxane (PDMS) improves the humidity resistance and VOC sensitivity of PDMS-coated dye/metal-organic frameworks (MOFs) composites. It also enhances their dispersion within liquid PDMS matrix, thereby promoting the hybrid liquid as high-quality extrusion-printing inks. The inks enable direct and precise printing on diverse substrates, forming a uniform and high particle-loading (70 wt%) film. The printed film on a flexible PDMS substrate demonstrates satisfactory flexibility and stretchability while retaining excellent sensing performance from dye/MOFs@PDMS particles. Further, the printed sensor array exhibits enhanced sensitivity to sub-ppm VOC levels, remarkable resistance to high relative humidity (RH) of 90%, and the differentiation ability for eight distinct VOCs. Finally, the wearable sensor proves practical by in situ monitoring of wheat scab-related VOC biomarkers. This study presents a versatile strategy for designing effective wearable gas sensors with widespread applications.

A Water-Driven and Low-Damping Triboelectric Nanogenerator Based on Agricultural Debris for Smart Agriculture.

The rapid progress in distributed electronics in agriculture depends on a wide range of energy supplies, such as cables and batteries. However, cable installation and maintenance are inconvenient in the agricultural environment, and the massive use of batteries will cause high replacement costs and serious environmental issues. To mitigate these problems, a water flow-driven and high-performance triboelectric nanogenerator based on agricultural debris (including derelict plant fibers and recycled greenhouse film) (AD-TENG) is developed. The precisely designed air gap and plant fiber-based dielectric brushes enable minimized frictional resistance and sustainable triboelectric charges, resulting in low damping and high performance for the AD-TENG. After nano-morphology modifications of the dielectric layer, the maximum power density of the AD-TENG increases by 64 times and reaches ≈1.24 W m-2 . The practical application demonstrates that the AD-TENG realizes the recycling of agricultural debris to achieve harvesting low-frequency and low-speed water-flow energy. Besides, the AD-TENG can be used to power agricultural sensors and develop the automatic irrigation system, which alleviates the energy consumption problem of agriculture and contributes to the realization of automated and informative intelligent agriculture.

Room-temperature high-precision printing of flexible wireless electronics based on MXene inks.

Wireless technologies-supported printed flexible electronics are crucial for the Internet of Things (IoTs), human-machine interaction, wearable and biomedical applications. However, the challenges to existing printing approaches remain, such as low printing precision, difficulty in conformal printing, complex ink formulations and processes. Here we present a room-temperature direct printing strategy for flexible wireless electronics, where distinct high-performance functional modules (e.g., antennas, micro-supercapacitors, and sensors) can be fabricated with high resolution and further integrated on various flat/curved substrates. The additive-free titanium carbide (Ti3C2Tx) MXene aqueous inks are regulated with large single-layer ratio (>90%) and narrow flake size distribution, offering metallic conductivity (~6, 900 S cm-1) in the ultrafine-printed tracks (3 µm line gap and 0.43% spatial uniformity) without annealing. In particular, we build an all-MXene-printed integrated system capable of wireless communication, energy harvesting, and smart sensing. This work opens a door for high-precision additive manufacturing of printed wireless electronics at room temperature.

A flexible virtual sensor array based on laser-induced graphene and MXene for detecting volatile organic compounds in human breath.

Detecting volatile organic compounds (VOCs) in human breath is critical for the early diagnosis of diseases. Good selectivity of VOC sensors is crucial for the accurate analysis of VOC biomarkers in human breath, which consists of more than 200 types of VOCs. In this paper, a flexible virtual sensor array (FVSA) was proposed based on a sensing layer of MXene and laser-induced graphene interdigital electrodes (LIG-IDEs) for detecting VOCs in exhaled human breath. The fabrication of LIG-IDEs avoids the costly and complicated procedures required for the preparation of traditional IDEs. The FVSA's responses of multiple parameters help build a unique fingerprint for each VOC, without a need for changing the temperature of the sensing element, which is commonly used in the VSA of semiconductor VOC sensors. Based on machine learning algorithms, we have achieved highly precise recognition of different VOCs and mixtures and accurate prediction (accuracy of 89.1%) of the objective VOC's concentration in variable backgrounds using this proposed FVSA. Moreover, a blind analysis validates the capacity of the FVSA to identify alcohol content in human breath with an accuracy of 88.9% using breath samples from volunteers before and after alcohol consumption. These results show that the proposed FVSA is promising for the detection of VOC biomarkers in human exhaled breath and early diagnosis of diseases.

Phase-dependent ion-to-electron transducing efficiency of WS2 nanosheets for an all-solid-state potentiometric calcium sensor.

Ultrathin metallic WS2 (M-WS2) nanosheets and semiconductive WS2 (S-WS2) nanosheets were exfoliated and for the first time employed as ion-to-electron transducing layer to construct an all-solid-state ion-selective electrode. Importantly, we found that the transducing efficiency of WS2 nanosheet-based solid-contact layer is phase-dependent. The M-WS2 nanosheets with larger content of 1 T-phase structure exhibit higher transducing efficiency than S-WS2 nanosheets, which can be ascribed to the remarkable conductivity of M-WS2 nanosheets. In order to demonstrate the excellent properties of the M-WS2 nanosheet-based tranducing layer, an all-solid-state calcium ion potentiometric sensor was constructed as the model. As expected, a Nernstian response (27.41 mV per decade, R2 = 0.9998) with a wide linear range of 1.0 × 10-5.0 to 1.0 × 10-2.0 M and a limit of detection of 2.0 µM was obtained. The developed all-solid-state potentiometric sensor using M-WS2 nanosheets as ion-to-electron transducing layer is expected to bring new progress for routine detection in various fields. Graphical Abstract Schematic illustration of the introduction of WS2 nanosheets with different phase structures as a new-generation solid-contact ion-to-electron transducing layer for all-solid-state potentiometric sensors.

Noble metal alloy nanoparticles coated flexible MoS2 paper for the determination of reactive oxygen species.

The monitoring of reactive oxygen species (ROS) in biological system has been occupying research hotspots recently, since the biochemical alterations caused by the overproduction of ROS are the main incentives of diseases and accelerated aging process. In this work, we proposed an effective and simple strategy for the construction of high-performance ROS electrochemical sensor. Noble metal alloy nanoparticles (AuPt nanoparticles) with high catalytic activity were spontaneously coated on the freestanding metallic molybdenum disulfide (MoS2) paper independent of any auxiliary conditions. Results have found that the abundant defects and electrons distributed on the metallic MoS2 paper could provide active sites for the nucleation and growth of noble metal nanoparticles. Besides, the excellent mechanical properties of the MoS2 paper promote the formation of flexible sensors. The fabricated MoS2 paper-based sensor was demonstrated to detect ROS with the advantages of wide linear range, prominent selectivity and flexibility, satisfactory detection stability, as well as simple and convenient preparation process. Furthermore, the desirable results obtained in the real sample experiments operated in plant extract pave the way for further real-time monitoring of plant physiological status to provide valuable information for guidance during plant growth.

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends.

From environmental monitoring to point-of-care biofluid analysis, rapid ion determination requires robust analytical tools. In recent years, driven by the development of materials science and processing technology, solid-contact ion-selective electrodes (SC-ISEs) with high-performance functional materials and creative structures have shown great potential for routine and portable ion detection. In particular, the introduction of nanomaterials as ion-to-electron transducers and the adoption of different performance enhancement strategies have significantly promoted the development of SC-ISEs. Besides, with the increasing miniaturization, flexibility, and dependability of SC-ISEs, this field has gradually begun to evolve from conventional potentiometric ion sensing to integrated sensing systems with broader application scenarios. This comprehensive review covers pioneering research on functional materials and state-of-the-art technologies for the construction of SC-ISEs, with an emphasis on new development trends and applications.

Self-reduction bimetallic nanoparticles on ultrathin MXene nanosheets as functional platform for pesticide sensing.

Two-dimensional (2D) transition metal carbides and nitrides, named MXene, appear promising application prospects in sensor filed. Metal nanoparticles, especially bimetallic nanoparticles, are the superior nanocatalyst, which process excellent features due to the high specific surface area and synergistic catalytic capacity. Using ultrathin MXene nanosheets as the natural reducing agent and support, we prepare the shape-controlled Au-Pd bimetallic nanoparticles via a self-reduction process at room temperature in a short time, which can well enhance the catalytic performance and are benefit for the acetylcholinesterase immobilization. Based on their desired properties, we propose a disposable electrochemical biosensor for the detection of organophosphorus pesticide using the multi-dimensional nanocomposites (MXene/Au-Pd) as the functional platform. Under the optimized conditions, our fabricated biosensor exhibits a favorable linear relationship with the concentration of paraoxon from 0.1 to 1000 µg L-1, with a low detection limit of 1.75 ng L-1. Furthermore, the biosensor can be applied for paraoxon detection in pear and cucumber samples, providing an effective and useful avenue for the applicability of novel 2D nanomaterials in biosensing field.

Two-dimensional MXene nanosheets (types Ti3C2Tx and Ti2CTx) as new ion-to-electron transducers in solid-contact calcium ion-selective electrodes.

Two kinds of two-dimensional MXene (of type Ti3C2Tx and Ti2CTx) nanosheets are described for use in solid-contact ion-selective electrodes (SC-ISEs) where they act as ion-to-electron transducers. Electrochemical characterizations show that the MXene-coated electrodes possess high double layer capacitance and enable rapid electron transport. This demonstrates the enhanced efficiency of MXene-based solid-contact layers to improve ion-electron transduction. Both Ti3C2Tx- and Ti2CTx-based SC-ISEs exhibited a Nernstian response (26.4 and 24.9 mV/decade, respectively) between 10-1 and 10-5.5 M Ca(II) concentrations with rapid response (<10 s) and low limits of detection (0.79 µM and 1.0 µM, respectively). The SC-ISEs display a lower charge impedance compared to ISEs without solid-contact layer. The new SC-ISEs possess outstanding potentiometric performance, extraordinary long-term stability, and insensitivity to light, CO2, O2, and redox couples, thus showing great promising prospect for routine sensing applications. Graphical abstractSchematic representation of MXene nanosheets for use as new intermediate layers in solid-contact ion-selective electrodes (SC-ISEs) for the potentiometric detection of calcium ion.