Vertical organic electrochemical transistors for complementary circuits.

Organic electrochemical transistors (OECTs) and OECT-based circuitry offer great potential in bioelectronics, wearable electronics and artificial neuromorphic electronics because of their exceptionally low driving voltages (<1 V), low power consumption (<1 µW), high transconductances (>10 mS) and biocompatibility1-5. However, the successful realization of critical complementary logic OECTs is currently limited by temporal and/or operational instability, slow redox processes and/or switching, incompatibility with high-density monolithic integration and inferior n-type OECT performance6-8. Here we demonstrate p- and n-type vertical OECTs with balanced and ultra-high performance by blending redox-active semiconducting polymers with a redox-inactive photocurable and/or photopatternable polymer to form an ion-permeable semiconducting channel, implemented in a simple, scalable vertical architecture that has a dense, impermeable top contact. Footprint current densities exceeding 1 kA cm-2 at less than ±0.7 V, transconductances of 0.2-0.4 S, short transient times of less than 1 ms and ultra-stable switching (>50,000 cycles) are achieved in, to our knowledge, the first vertically stacked complementary vertical OECT logic circuits. This architecture opens many possibilities for fundamental studies of organic semiconductor redox chemistry and physics in nanoscopically confined spaces, without macroscopic electrolyte contact, as well as wearable and implantable device applications.

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.

Flexible complementary circuits operating at sub-0.5 V via hybrid organic-inorganic electrolyte-gated transistors.

Electrolyte-gated transistors (EGTs) hold great promise for next-generation printed logic circuitry, biocompatible integrated sensors, and neuromorphic devices. However, EGT-based complementary circuits with high voltage gain and ultralow driving voltage (<0.5 V) are currently unrealized, because achieving balanced electrical output for both the p- and n-type EGT components has not been possible with current materials. Here we report high-performance EGT complementary circuits containing p-type organic electrochemical transistors (OECTs) fabricated with an ion-permeable organic semiconducting polymer (DPP-g2T) and an n-type electrical double-layer transistor (EDLT) fabricated with an ion-impermeable inorganic indium-gallium-zinc oxide (IGZO) semiconductor. Adjusting the IGZO composition enables tunable EDLT output which, for In:Ga:Zn = 10:1:1 at%, balances that of the DPP-g2T OECT. The resulting hybrid electrolyte-gated inverter (HCIN) achieves ultrahigh voltage gains (>110) under a supply voltage of only 0.7 V. Furthermore, NAND and NOR logic circuits on both rigid and flexible substrates are realized, enabling not only excellent logic response with driving voltages as low as 0.2 V but also impressive mechanical flexibility down to 1-mm bending radii. Finally, the HCIN was applied in electrooculographic (EOG) signal monitoring for recording eye movement, which is critical for the development of wearable medical sensors and also interfaces for human-computer interaction; the high voltage amplification of the present HCIN enables EOG signal amplification and monitoring in which a small ∼1.5 mV signal is amplified to ∼30 mV.

A Simplified Amplification-Free Strategy with Lyophilized CRISPR-CcrRNA System for Drug-Resistant Salmonella Detection.

Drug resistance in pathogenic bacteria has become a major threat to global health. The misuse of antibiotics has increased the number of resistant bacteria in the absence of rapid, accurate, and cost-effective diagnostic tools. Here, an amplification-free CRISPR-Cas12a time-resolved fluorescence immunochromatographic assay (AFC-TRFIA) is used to detect drug-resistant Salmonella. Multi-locus targeting in combination crRNA (CcrRNA) is 27-fold more sensitive than a standalone crRNA system. The lyophilized CRISPR system further simplifies the operation and enables one-pot detection. Induction of nucleic acid fixation via differentially charged interactions reduced the time and cost required for flowmetric chromatography with enhanced stability. The induction of nucleic acid fixation via differentially charged interactions reduces the time and cost required for flowmetric chromatography with enhanced stability. The platform developed for the detection of drug-resistant Salmonella has an ultra-sensitive detection limit of 84 CFU mL-1 within 30 min, with good linearity in the range of 102 -106 CFU mL-1 . In real-world applications, spiked recoveries range from 76.22% to 145.91%, with a coefficient of variation less than 10.59%. AFC-TRFIA offers a cost-effective, sensitive, and virtually equipment-independent platform for preventing foodborne illnesses, screening for drug-resistant Salmonella, and guiding clinical use.

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.

Recent Advances in g-C3 N4 -Based Photocatalysts for Pollutant Degradation and Bacterial Disinfection: Design Strategies, Mechanisms, and Applications.

Emerging photocatalytic technology promises to provide an effective solution to the global energy crisis and environmental pollution. Graphite carbon nitride (g-C3 N4 ) has gained extensive attention in the scientific community due to its excellent physical and chemical properties, attractive electronic band structure, and low cost. In this paper, research progress in design strategies for g-C3 N4 -based photocatalysts in the past five years is reviewed from the perspectives of nanostructure construction, element doping, and heterostructure construction. To clarify the relationship between application requirements and structural design, variations in the morphology, electronic energy band structure, light absorption capacity, as well as interfacial charge transfer caused by various modification strategies are discussed in detail. The recent applications of g-C3 N4 -based photocatalysts for pollutant degradation and bacterial disinfection are reviewed, as well as the antimicrobial activity and degradation mechanisms. Finally, current challenges and future development directions for the practical application of g-C3 N4 -based photocatalysts are tentatively discussed.

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.

Fluorinated Graphene-Enabled Durable Triboelectric Coating for Water Energy Harvesting.

The durability issue of triboelectric nanogenerators (TENGs) still limits its practical application for long-term operation, especially in harvesting water energy, which is one of the most widespread energies in nature. Attempting to ameliorate this, fluorinated graphene (FG) with unique triboelectric negativity and superhydrophobic property is introduced to serve as a new triboelectric and protective layer for TENG construction. The self-cleaning as well as anti-corrosion property and durability of the FG coating-enabled TENG device is then demonstrated. Furthermore, this novel triboelectronegative material candidate is applied for consecutively coating on Cu mesh and the inner wall of sewage pipe to fabricate TENGs for water energy harvesting and working as a metal protective layer in the meantime. Through the extraordinary output performance, the feasibility of FG-enabled triboelectric coating to be used in the field of interference screening, filtering, and sewage pipes is proved. This developed triboelectronegative coating not only broadens the material selection of TENG but also significantly enhances the durability and robustness of TENG for water energy harvesting, which possesses great potential in applying in metal protection and water energy harvesting under extreme conditions (e.g., strong acid and strong alkaline environments).

Growth-Controllable Triboelectric Nanogenerator Based on Surface-Attached Metal-Organic Framework Layer on Living Leaf.

Plant nanoelectronics aims to achieve specific functions by selecting suitable nanomaterials to connect or implant into plants. In this work, a new cyclic-spraying method is developed to attain controllable growth of surface-attached metal-organic framework (SURMOF) coatings on various complex substrates, including cotton, silk, and plant leaves. The covalent bonds formed between the SURMOF layer and substrate enable them to connect firmly without additional adhesive and do not fall off from the microstructured substrate surface with the change of biological activity or environment. Noteworthily, the triboelectric polarity of SURMOF can be regulated by changing the ligand molecule. As a proof of concept, a growth-controllable triboelectric nanogenerator (GC-TENG) based on living leaves and coated SURMOF layer is developed, and the feasibility of using it in the self-driven agricultural monitoring system is explored. In addition, long-term monitoring results show that the growth of SURMOF coating will not cause damage to plant leaf tissue, nor will it affect plant photosynthesis.

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.

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.

Recent Advances in Nanomaterial-Enabled Wearable Sensors: Material Synthesis, Sensor Design, and Personal Health Monitoring.

Wearable sensors have gained much attention due to their potential in personal health monitoring in a timely, cost-effective, easy-operating, and noninvasive way. In recent studies, nanomaterials have been employed in wearable sensors to improve the sensing performance in view of their excellent properties. Here, focus is mainly on the nanomaterial-enabled wearable sensors and their latest advances in personal health monitoring. Different kinds of nanomaterials used in wearable sensors, such as metal nanoparticles, carbon nanomaterials, metallic nanomaterials, hybrid nanocomposites, and bio-nanomaterials, are reviewed. Then, the progress of nanomaterial-based wearable sensors in personal health monitoring, including the detection of ions and molecules in body fluids and exhaled breath, physiological signals, and emotion parameters, is discussed. Furthermore, the future challenges and opportunities of nanomaterial-enabled wearable sensors are discussed.

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.

Magnetic particles for integrated nucleic acid purification, amplification and detection without pipetting.

Nucleic acid amplification based detection plays an important role in food safety, environmental monitoring and clinical diagnosis. However, traditional nucleic acid detection process involves transferring liquid from one tube to another by pipetting. It requires trained persons, equipped labs and consumes lots of time. The ideal nucleic acid detection is integrated, closed, simplified and automated. Magnetic particles actuated by magnetic fields can efficiently adsorb nucleic acids and promote integrated nucleic acid assays without pipetting driven by pumps and centrifuges. We will comprehensively review magnetic particles assisted integrated system for nucleic acid detection and hope it can inspire further related study.

Recent developments in strontium-based biocomposites for bone regeneration.

Recent advances in biomaterial designing techniques offer immense support to tailor biomimetic scaffolds and to engineer the microstructure of biomaterials for triggering bone regeneration in challenging bone defects. The current review presents the different categories of recently explored strontium-integrated biomaterials, including calcium silicate, calcium phosphate, bioglasses and polymer-based synthetic implants along with their in vivo bone formation efficacies and/or in vitro cell responses. The role and significance of controlled drug release scaffold/carrier design in strontium-triggered osteogenesis was also comprehensively described. Furthermore, the effects of stem cells and growth factors on bone remodeling are also elucidated.

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.

Colorimetric aggregation assay for kanamycin using gold nanoparticles modified with hairpin DNA probes and hybridization chain reaction-assisted amplification.

The authors describe a colorimetric method for determination of kanamycin by using gold nanoparticles (AuNPs) as the element of signal-conversion and by applying hybridization chain reaction-assisted signal amplification. The assay is carried out by monitoring the absorbance change and color change adding salt to the reaction solution containing kanamycin (analyte), hairpin DNA probe, and AuNPs. Three hairpin DNA probes with sticky ends were absorbed on the AuNPs via their sticky ends. Cating with DNA prevents them from salt-induced aggregation (which leads to a color change from red to blue) in the complete absence of kanamycin. In contrast, in the presence of kanamycin, the aptamer hairpin DNA probe binds kanamycin, and the newly exposed section of DNA triggers a cascade of hybridization chain reactions with formation of numerous dsDNAs. On addition of salt, the AuNPs form blue aggregates due to the repulsion between dsDNA and AuNPs. Under optimal conditions, the ration of absorbance at 520 and 630 nm drops with the kanamycin concentration in the range from 1 to 40 µM, and the limit of detection is 0.68 µM. The assay can selectively distinguish kanamycin from other antibiotics. The method was applied to kanamycin detection in (spiked) milk samples and gave excellent recoveries. Graphical abstract Schematic presentation of colorimetric method for kanamycin detection using gold nanoparticles modified with hairpin DNA probes and hybridization chain reaction-assisted amplification.

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.

A disposable electrochemical sensor based on electrospinning of molecularly imprinted nanohybrid films for highly sensitive determination of the organotin acaricide cyhexatin.

Nanofibrous polyporous membranes imprinted with cyhexatin (CYT) were formed via the ordered distribution of the imprints in electrospun nanofibers. The MIPs have a high mass transfer rate and enhanced adsorption capacity. In addition, a printed carbon electrode with enhanced sensitivity was developed via electrochemical fabrication of reduced graphene oxide (rGO) and gold nanoparticles (AuNPs). The molecularly imprinted sensor exhibits excellent selectivity and sensitivity for CYT. The structure and morphology of the nanohybrid films were characterized by using scanning electron microscopy, atomic force microscopy and chronoamperometry. The sensing performances were evaluated by cyclic voltammetry, differential pulse voltammetry and electrochemical impedance spectroscopy by using hexacyanoferrate(IV) as an electrochemical probe. The electrode, best operated at a working potential of around 0.16 V (vs. Ag/AgCl), has a linear response in the 1-800 ng mL-1 CYT concentration range and a detection limit of 0.17 ng mL-1 (at S/N = 3). The sensor demonstrated satisfactory recoveries when applied to the determination of CYT in spiked pear samples. Graphical abstract Schematic presentation of the electrochemical sensor for detection of CYT.

Fully Written Flexible Potentiometric Sensor Using Two-Dimensional Nanomaterial-Based Conductive Ink.

The emerging demand for flexible, portable, easily accessible, and cost-effective electronic fabrication has motivated the development of novel techniques to manufacture electronic components and devices. Inspired by daily hand-writing, an all-written potentiometric sensor was developed by using a Chinese brush pen-based writing technique. A writing ink made from graphene nanosheet (GN) as a conductive component, Triton X-100 as a stabilizer, and xanthan gum as a binder, was used to obtain flexible electrode substrate. Results demonstrate the GN ink-based writing electrode (GN-WE) possesses good conductivity, fast electron-transfer kinetics, considerable stability, and favorable flexibility. By further writing cadmium ion selective membrane (Cd2+-ISM) and photopolymerized reference membrane (RM) on the surface of GN-WE, an all-solid-state potentiometric sensor for cadmium ion was constructed. A large bulk capacitance (41.67 µF) and excellent potential stability (drift of 0.156 mV h-1) were achieved at the developed all-written potentiometric sensor, which is much superior to the solid-contact potentiometric sensor using GCE as electrode substrate. Furthermore, real sample analysis reveals that our GN ink-based potentiometric sensor could be used as a reliable and stable sensor for cadmium ion detection in food and in the environment.