Highly Sensitive Glucose Biosensors Based on Organic Electrochemical Transistors Using Platinum Gate Electrodes Modified with Enzyme and Nanomaterials

Organic electrochemical transistors with glucose oxidase‐modified Pt gate electrodes are successfully used as highly sensitive glucose sensors. The gate electrodes are modified with nanomaterials (multi‐wall carbon nanotubes or Pt nanoparticles) for the first time, which results in a dramatic improvement in the sensitivity of the devices. The detection limit of the device modified with Pt nanoparticles on the gate electrode is about 5 nM, which is three orders of magnitude better than a device without the nanoparticles. The improvement of the device performance can be attributed to the excellent electrocatalytic properties of the nanomaterials and more effective immobilization of enzyme on the gate electrodes. Based on the same principle, many other types of enzyme sensors with high sensitivity and low cost are expected to be realized by modifying the gate electrodes of organic electrochemical transistors with specific enzymes and nanomaterials.     

Laser Direct Writing of Ultrahigh Sensitive SiC‐Based Strain Sensor Arrays on Elastomer toward Electronic Skins

Electronic skins (e‐skins) have been widely investigated as important platforms for healthcare monitoring, human/machine interfaces, and soft robots. However, mask‐free formation of patterned active materials on elastomer substrates without involving high‐cost and complicate processes is still a grand challenge in developing e‐skins. Here, SiC‐based strain sensor arrays are fabricated on elastomer for e‐skins by a laser direct writing (LDW) technique, which is mask‐free, highly efficient, and scalable. The direct synthesis of active material on elastomer is ascribed to the LDW‐induced conversion of siloxanes to SiC. The SiC‐based devices own a highest sensitivity of ≈2.47 × 10⁵ achieved at a laser power of 0.8 W and a scanning velocity of 1.25 mm s^?1. Moreover, the LDW‐developed device provides a minimum strain detection limit of 0.05%, a small temperature drift, and a high mechanical durability for over 10 000 cycles. When it is mounted onto human skins, the SiC‐based device is able to monitor external stimuli and human health conditions, with the capability of wireless data transmission. Its potential application in e‐skins is further proved by an LDW‐fabricated device having 3 × 3 SiC sensor array for tactile sensing.     

In Situ Synthesis of Mechanically Robust,Transparent Nanofiber-Reinforced Hydrogels for Highly Sensitive Multiple Sensing

Hydrogels that are both highly conductive and mechanically robust have demonstrated great potential in various applications ranging from healthcare to soft robotics; however, the creation of such materials remains an enormous challenge. This study presents an in situ synthesis strategy for developing bioinspired chemically integrated silica-nanofiber-reinforced hydrogels (SFRHs) with robust mechanical and electronic performance. The strategy is to synthesize soft hydrogel matrices from acrylamide monomers in the presence of well-dispersed silica nanofibers and vinyl silane, which generates homogenous SFRHs with innovative interfacial chemical bonds. The resultant SFRHs exhibit excellent mechanical properties including high mechanical strength of 0.3 MPa at a fracture strain of 1400%, high Young's modulus of 0.11 MPa (comparable to human skin), and superelasticity over 1000 tensile cycles without plastic deformation, while maintaining high transmittance (≥83%). In parallel, the SFRHs show enhanced ionic conductivity (3.93 S m⁻¹) and can monitor multiple stimuli (stretching, compressing, and bending) with high sensitivity (gauge factor of 2.67) and ultra-durability (10 000 cycles). This work may shed light on the design and development of tough and stretchable hydrogels for various applications.     

Porous Fibers Composed of Polymer Nanoball Decorated Graphene for Wearable and Highly Sensitive Strain Sensors

Wearable textile strain sensors that can perceive and respond to human stimuli are an essential part of wearable electronics. Yet, the detection of subtle strains on the human body suffers from the low sensitivity of many existing sensors. Generally, the inadequate sensitivity originates from the strong structural integrity of the sensors because tiny external strains cannot trigger enough variation in the conducting network. Inspired by the rolling friction where the interaction is weakened by decreasing interface area, porous fibers made of graphene decorated with nanoballs are prepared via a prolonged phase‐separation process. This novel structure confers the graphene fibers with high gauge factors (51 in 0–5% and 87 in 5–8%), which is almost 10 times larger than the same structures without nanoballs. A low detection limit (0.01% strain) and good durability (over 6000 circles) are obtained. By the virtue of these qualities, these fiber‐based textile sensors can recognize a pulse wave and eyeball movement in real‐time while keeping comfortable wearing sense. Moreover, by weaving such fibers, the electronic fabrics with a specially designed structure can distinguish the multilocation in real time, which shows great potential as wearable electronics.     

Transparent,Flexible, and Highly Sensitive Piezocomposite Capable of Harvesting and Monitoring Kinetic Movements of Microbubbles in Liquid

In this study, a zinc oxide (ZnO)-decorated nickel microfiber (ZNMF)-based piezoelectric nanogenerator (ZNMF-PENG) using electrospinning, metal electroplating, electrospraying, and ceramic growing techniques is fabricated. The combination of these techniques enables the ZNMF-PENG to possess high transparency and flexibility that are difficult to achieve through the existing piezoceramic-based PENGs. In particular, the presence of innumerable piezoceramic ZnO nanowires inside the ZNMF-PENG allows for detecting microbubble movements having an extremely low buoyancy force of 0.009 N, which is beneficial for detecting cavitation. Moreover, in comparison to previously reported PENGs fabricated using an electrospinning technique, the ZNMF-PENG demonstrates the highest energy-harvesting efficiency of 8750 V N⁻¹ m⁻². The novel approach in materials and methods proposed in this study is expected to contribute to the further advancement in developing transparent, flexible, and performance-improved PENGs applicable to various industrial applications.     

Hybrid Organic/Inorganic Nanostructures for Highly Sensitive Photoelectrochemical Detection of Dissolved Oxygen in Aqueous Media

Precise, reliable, and remote measurement of dissolved oxygen in aqueous media is of great importance for many industrial, environmental, and biological applications. In particular, photoelectrochemical sensors working in differential mode have recently demonstrated promising properties, in terms of stability, sensitivity, and application potential. Here, a new approach is presented, combining visible light sensitivity, efficient photocurrent generation, and solution‐processed fabrication methods of conjugated polymers, with charge carriers selectivity, energetic alignment favorable to efficient interfacial charge transfer and high surface area achievable by using metal oxide nanostructures. Extensive characterization and optimization of the hybrid organic/inorganic system are carried out, leading to the realization of an oxygen sensor device, based on nanostructured palladium oxide/poly[(9,9‐dioctylfluorenyl‐2,7‐diyl)‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole]/[6,6]phenyl‐C61‐butyric acid methyl ester (PdO/APFO‐3:PCBM) as materials of choice. State‐of‐the‐art sensitivity, amounting at ?5.87 μA cm^?2 ppm^?1, low background signal, in the order of ?4.85 μA cm^?2, good electrochemical stability for more than 2 h of continuous functioning and high reproducibility of the signal over the pH 1 to 10 range, are reported, making the hybrid device suitable for several practical uses. The results fully validate the mixed organic/inorganic approach for photoelectrochemical applications, and pave the way for its further exploitation in fields like waste water treatment, environmental monitoring, and water splitting.     

Gold‐Nanocluster‐Based Fluorescent Sensors for Highly Sensitive and Selective Detection of Cyanide in Water

A novel, gold‐nanocluster‐based fluorescent sensor for cyanide in aqueous solution, which is based on the cyanide etching‐induced fluorescence quenching of gold nanoclusters, is reported. In addition to offering high selectivity due to the unique Elsner reaction between cyanide and the gold atoms of gold nanoclusters, this facile, environmentally friendly and cost‐effective method provides high sensitivity. With this sensor, the lowest concentration to quantify cyanide ions could be down to 200 × 10^?9 M , which is approximately 14 times lower than the maximum level (2.7 × 10^?6 M ) of cyanide in drinking water permitted by the World Health Organization (WHO). Furthermore, several real water samples spiked with cyanide, including local groundwater, tap water, pond water, and lake water, are analyzed using the sensing system, and experimental results show that this fluorescent sensor exhibits excellent recoveries (over 93%). This gold‐nanocluster‐based fluorescent sensor could find applications in highly sensitive and selective detection of cyanide in food, soil, water, and biological samples.     

A Simple and Innovative Route to Prepare a Novel Carbon Nanotube/Prussian Blue Electrode and its Utilization as a Highly Sensitive H2O2 Amperometric Sensor

The utilization of iron‐based species (mainly metallic iron, hematite and magnetite) encapsulated into multi‐walled carbon nanotubes (CNTs) as reactants in an electrochemical synthesis is reported for the first time in this work. Prussian blue (PB) is electrosynthesized in a heterogeneous reaction between ferricyanide ions in aqueous solution and the iron‐species encapsulated into CNTs, resulting in novel CNT/PB paste electrodes. This innovative preparation route produces an intimate contact between the PB and the CNTs, which improves the stability and redox properties of PB. The PB formation and the chemical interaction between the PB and the CNTs are confirmed by Raman spectroscopy. The electrode is employed as a hydrogen peroxide amperometric sensor, resulting in a very low limit of detection (1.94 × 10^?8 mol L^?1) and very high sensitivity (15.3 A cm^?2 M ^?1).     

Fluorescence‐Amplifying Detection of Hydrogen Peroxide with Cationic Conjugated Polymers,and Its Application to Glucose Sensing

A highly sensitive hydrogen peroxide probe that takes advantage of the amplified fluorescence quenching of conjugated polymers has been developed. The cationic conjugated polymer, poly(9,9‐bis(6′‐N,N,N‐trimethylammonium‐hexyl) fluorene phenylene) (PFP‐NMe₃⁺) and peroxyfluor‐1 with boronate protecting groups (Fl‐BB) are used to detect H₂O₂ optically. Without the addition of H₂O₂, the absence of electrostatic interactions between the cationic PFP‐NMe₃⁺ and the neutral Fl‐BB keeps the Fl‐BB well separated from the PFP‐NMe₃⁺, and no fluorescence quenching of the PFP‐NMe₃⁺ occurs. In the presence of H₂O₂, the formation of the anionic quencher, fluorescein, by specific reaction of the Fl‐BB with H₂O₂ results in strong electrostatic interactions between the PFP‐NMe₃⁺ and the fluorescein, and therefore efficient fluorescence quenching of the PFP‐NMe₃⁺ occurs. The absorption of fluorescein overlaps the emission of PFP‐NMe₃⁺, which encourages fluorescence resonance energy transfer (FRET) from the PFP‐NMe₃⁺ to the fluorescein. The H₂O₂ probe has very good sensitivity, with a detection range of 15 to 600 nM. Since glucose oxidase (GOx) can specifically catalyze the oxidation of β‐D ‐(+)‐glucose to generate H₂O₂, glucose detection is also realized with the H₂O₂ probe as the signal transducer.     

A Cruciform Electron Donor–Acceptor Semiconductor with Solid‐State Red Emission: 1D/2D Optical Waveguides and Highly Sensitive/Selective Detection of H2S Gas

In this paper, a new cruciform donor–acceptor molecule 2,2'‐((5,5'‐(3,7‐dicyano‐2,6‐bis(dihexylamino)benzo[1,2‐b:4,5‐b']difuran‐4,8‐diyl)bis(thiophene‐5,2‐diyl))bis (methanylylidene))dimalononitrile ( BDFTM ) is reported. The compound exhibits both remarkable solid‐state red emission and p‐type semiconducting behavior. The dual functions of BDFTM are ascribed to its unique crystal structure, in which there are no intermolecular face‐to‐face π–π interactions, but the molecules are associated by intermolecular CN…π and H‐bonding interactions. Firstly, BDFTM exhibits aggregation‐induced emission; that is, in solution, it is almost non‐emissive but becomes significantly fluorescent after aggregation. The emission quantum yield and average lifetime are measured to be 0.16 and 2.02 ns, respectively. Crystalline microrods and microplates of BDFTM show typical optical waveguiding behaviors with a rather low optical loss coefficient. Moreover, microplates of BDFTM can function as planar optical microcavities which can confine the emitted photons by the reflection at the crystal edges. Thin films show an air‐stable p‐type semiconducting property with a hole mobility up to 0.0015 cm²V^?1s^?1. Notably, an OFET with a thin film of BDFTM is successfully utilized for highly sensitive and selective detection of H₂S gas (down to ppb levels).     

Living Cells Directly Growing on a DNA/Mn3(PO4)2‐Immobilized and Vertically Aligned CNT Array as a Free‐Standing Hybrid Film for Highly Sensitive In Situ Detection of Released Superoxide Anions

It is important to detect reactive oxygen species (ROS) in situ for investigation of various critical biological processes, and this is however very challenging because of the limited sensitivity or/and selectivity of existing methods that are mainly based on sensing ROS released by cells with short lifetimes and low concentrations in a culture medium. Here, a new approach is reported to directly grow living cells on DNA/Mn₃(PO₄)₂‐immobilized and vertically aligned carbon nanotube (VACNT) array nanostructure as a smart free‐standing hybrid film, of which the DNA/Mn₃(PO₄)₂ and VACNT provide high electroactivity and excellent electron transport, respectively, while the directly grown cell on the nanostructure offers short diffusion distance to reaction sites, thus constructing a highly sensitive in situ method for detection of cancer‐cell‐released ROS under drug stimulations. Compared to the measured ROS released by cells in a culture medium, the detection sensitivity with this constructed hybrid film increases by more than six times, which implies that ROS molecules (superoxide anions) secreted from living cells are immediately captured by this smart structure without diffusion process or with extremely short diffusion distance. This design considerably reduces the time from release to detection of the target molecules, minimizing the potential molecular decay due to the short lifetime or high reactivity.