Oligotriphenylene Nanofiber Sensors for Detection of Nitro‐Based Explosives

Blue light‐emitting oligotriphenylene nanofibers are synthesized by oxidizing triphenylene using ferric chloride. By adjusting the monomer concentration, the acid used, and the temperature employed, the average diameter and length of the nanofibers can be readily tuned from 50 to 200 nm and 0.5 to 5 μm, respectively. Structural characterization, electrical conductivity, thermal stability, and fluorescence of oligotriphenylene, along with a proposed nanofiber formation mechanism, are presented. Both oligotriphenylene nanofiber dispersions and oligotriphenylene/polysulfone composite films are developed as fluorescent sensors for detecting traces of nitro‐based explosives including nitromethane, nitrobenzene, and 2,4,6‐trinitrophenol, as well as an electron‐deficient metal ion, Fe(III). The sensors exhibit much better selectivity and sensitivity compared to conventional sensors, with detection limits down to 1.0 nm with a detection range covering ～4 orders of magnitude. The detection mechanism of the fluorescent sensors is also disscussed.     

Novel Signal‐Amplifying Fluorescent Nanofibers for Naked‐Eye‐Based Ultrasensitive Detection of Buried Explosives and Explosive Vapors

A novel electrospun fluorescent nanofiberous membrane with a function like “molecular wires” was developed via electrospinning for the detection of ultra‐trace nitro explosive vapors and buried explosives by naked eye under UV excitation. The high binding affinity between the electron‐deficient nitro explosives and the sensing film results in a rapid, dramatic quenching in its fluorescence emission. A wide spectrum of nitro explosives, in particular, TNT, Tetryl, RDX, PETN and HMX could be “visually” detected at their sub‐equilibrium vapors (less than 10 ppb, 74 ppt, 5 ppt, 7 ppt and 0.1 ppt, respectively) released from 1 ng explosives residues. Such outstanding sensing performance could be attributed to the proposed “sandwich‐like” conformation between pyrene and phenyl pendants of PS which may allow efficient long‐range energy migration similar to “molecular wire”, thus achieving amplified fluorescence quenching. Its application for the detection of buried explosives in soil by naked eye was also demonstrated, indicating its potential application for landmine mapping. To the best of our knowledge, this is the first report about the detection of buried explosives without the use of any advanced analytical instrumentation.     

Seeing Hydrogen in Colors: Low‐Cost and Highly Sensitive Eye Readable Hydrogen Detectors

There is a great interest in the development of reliable and low‐cost hydrogen sensors for applications in the hydrogen economy, industrial processes, space application, detection of environmental pollution, and biomedical applications. Here, a new type of optical detector that indicates the presence of hydrogen in concentration range 5 ppm to 0.1 vol% H₂ merely by a reversible and tunable color change is reported. The device takes advantage of the reversible change in optical properties of a Pd‐capped Y thin film upon exposure to H₂, while the color is tuned using the interference of light reflected between the Y and Pd layers. In this way, an eye‐readable optical sensor that circumvents the need for electronics and external digital readouts is created. Using surface modifications, the performance of the H₂ detector in humid and oxygen rich environment is greatly improved. Therefore, the device has the potential to be used for chemical and also biochemical/biomedical H₂ sensing applications such as breathe hydrogen tests.     

Light‐Boosting Highly Sensitive Pressure Sensors Based on Bioinspired Multiscale Surface Structures

Pressure sensors have attracted tremendous attention because of their potential applications in the fields of health monitoring, human–machine interfaces, artificial intelligence, and so on. Improving pressure‐sensing performances, especially the sensitivity and the detection limit, is of great importance to expand the related applications, however it is still an enormous challenge so far. Herein, highly sensitive piezoresistive pressure sensors are reported with novel light‐boosting sensing performances. Rose petal–templated positive multiscale millimeter/micro/nanostructures combined with surface wrinkling nanopatterns endow the assembled pressure sensors with outstanding pressure sensing performance, e.g. an ultrahigh sensitivity (70 KPa^?1, <0.5 KPa), an ultralow detection limit (0.88 Pa), a wide pressure detect ion range (from 0.88 Pa to 32 KPa), and a fast response time (30 ms). Remarkably, simple light illumination further enhances the sensitivity to 120 KPa^?1 (<0.5 KPa) and lowers the detection limit to 0.41 Pa. Furthermore, the flexible light illumination offers unprecedented capabilities to spatiotemporally control any target in multiplexed pressure sensors for optically enhanced/tailorable sensing performances. This light‐control strategy coupled with the introduction of bioinspired multiscale structures is expected to help design next generation advanced wearable electronic devices for unprecedented smart applications.     

Interfacial Self‐Assembly of Amphiphilic Dual Temperature Responsive Actuating Janus Particles

Amphiphilic Janus particles feature the combination of two different functional materials in one single colloid, as well as the possibility of self‐assembly at interfaces into complex superstructures. In this article, the self‐assembly of dual temperature responsive amphiphilic Janus particles at liquid–liquid interfaces and their subsequent conversion into an actuating layer‐shaped surface are presented. These microparticles are produced in a capillaries based continuous flow microfluidic device by photoinitiated radical polymerization. The hydrophobic part of the Janus particles contains a liquid crystalline elastomer (LCE), which performs a strong actuation up to 95% during the nematic–isotropic phase transition. The other side consists of a p(NIPAAm) hydrogel, which features volumetric expansions up to 280% below the lower critical solution temperature. A multistep molding process is developed to uniformly align the Janus particles at a toluene/water boundary surface and to embed the particles into a hydrogel matrix. A particle covered hydrogel layer is obtained, which features a collective actuation of the rod‐like LCE parts on the surface and a bundling of the resulting forces during the phase transition.     

Ultrasensitive and Highly Selective Gas Sensors Based on Electrospun SnO2 Nanofibers Modified by Pd Loading

This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO₂ fibers. Unloaded and Pd‐loaded SnO₂ nanofiber mats are synthesized by electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO₂ crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO₂ crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO₂ grain growth during the calcination step. The Pd‐loaded SnO₂ sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H₂ and lower sensitivity to NO₂ compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO₂ crystallites and catalytic effect of PdO in promoting the oxidation of H₂ into H₂O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.     

Gas Sensors: Ultrasensitive and Highly Selective Gas Sensors Based on Electrospun SnO2 Nanofibers Modified by Pd Loading (Adv. Funct. Mater. 24/2010)

This work presents a new route to suppress grain growth and tune the sensitivity and selectivity of nanocrystalline SnO₂ fibers. Unloaded and Pd‐loaded SnO₂ nanofiber mats are synthesized by electrospinning followed by hot‐pressing at 80 °C and calcination at 450 or 600 °C. The chemical composition and microstructure evolution as a function of Pd‐loading and calcination temperature are examined using EDS, XPS, XRD, SEM, and HRTEM. Highly porous fibrillar morphology with nanocrystalline fibers comprising SnO₂ crystallites decorated with tiny PdO crystallites is observed. The grain size of the SnO₂ crystallites in the layers that are calcined at 600 °C decreases with increasing Pd concentration from about 15 nm in the unloaded specimen to about 7 nm in the 40 mol% Pd‐loaded specimen, indicating that Pd‐loading could effectively suppress the SnO₂ grain growth during the calcination step. The Pd‐loaded SnO₂ sensors have 4 orders of magnitude higher resistivity and exhibit significantly enhanced sensitivity to H₂ and lower sensitivity to NO₂ compared to their unloaded counterparts. These observations are attributed to enhanced electron depletion at the surface of the PdO‐decorated SnO₂ crystallites and catalytic effect of PdO in promoting the oxidation of H₂ into H₂O. These phenomena appear to have a much larger effect on the sensitivity of the Pd‐loaded sensors than the reduction in grain size.     

Bioinspired Anisotropic Hydrogel Actuators with On–Off Switchable and Color‐Tunable Fluorescence Behaviors

An effective approach to develop a novel macroscopic anisotropic bilayer hydrogel actuator with on–off switchable fluorescent color‐changing function is reported. Through combining a collapsed thermoresponsive graphene oxide‐poly(N‐isopropylacrylamide) (GO‐PNIPAM) hydrogel layer with a pH‐responsive perylene bisimide‐functionalized hyperbranched polyethylenimine (PBI‐HPEI) hydrogel layer via macroscopic supramolecular assembly, a bilayer hydrogel is obtained that can be tailored and reswells to form a 3D hydrogel actuator. The actuator can undergo complex shape deformation caused by the PNIPAM outside layer, then the PBI‐HPEI hydrogel inside layer can be unfolded to trigger the on–off switch of the pH‐responsive fluorescence under the green light irradiation. This work will inspire the design and fabrication of novel biomimetic smart materials with synergistic functions.     

Ionic Tactile Sensors for Emerging Human‐Interactive Technologies: A Review of Recent Progress

Ionic tactile sensors (ITS) represent a new class of deformable sensory platforms that mimic not only the tactile functions and topological structures but also the mechanotransduction mechanism across the biological ion channels in human skin, which can demonstrate a more advanced biological interface for targeting emerging human‐interactive technologies compared to conventional e‐skin devices. Recently, flexible and even stretchable ITS have been developed using novel structural designs and strategies in materials and devices. These skin‐like tactile sensors can effectively sense pressure, strain, shear, torsion, and other external stimuli with high sensitivity, high reliability, and rapid response beyond those of human perception. In this review, the recent developments of the ITS based on the novel concepts, structural designs, and strategies in materials innovation are entirely highlighted. In particular, biomimetic approaches have led to the development of the ITS that extend beyond the tactile sensory capabilities of human skin such as sensitivity, pressure detection range, and multimodality. Furthermore, the recent progress in self‐powered and self‐healable ITS, which should be strongly required to allow human‐interactive artificial sensory platforms is reviewed. The applications of ITS in human‐interactive technologies including artificial skin, wearable medical devices, and user‐interactive interfaces are highlighted. Last, perspectives on the current challenges and the future directions of this field are presented.     

Polymer Nanocomposites Containing Carbon Nanofibers as Soft Printable Sensors Exhibiting Strain‐Reversible Piezoresistivity

Designed as flexible and extendable conductive print media for pervasive computing as strain sensors, nanocomposites composed of a plasticized thermoplastic or a cross‐linked elastomer and containing carbon nanofibers at concentrations just above the percolation threshold are observed to exhibit a uniquely strain‐reversible piezoresistive response upon application of quasi‐static tensile strain. At small strain levels, the electrical resistance of these nanocomposites reduces with increasing strain, indicative of negative piezoresistivity. Beyond a critical strain, however, the resistance reverses and increases with increasing strain, revealing the existence of a negative‐to‐positive piezoresistivity transition that is fully strain‐reversible and repeatable upon strain cycling. These characteristics imply that the nanocomposite morphologies are highly stable with little evidence of mechanical hysteresis. The mechanism underlying this transition is attributed to reorientation of high‐aspect‐ratio nanofibers (initially homogeneously dispersed) at low strains, followed by separation at high strains. While deposition of these nanocomposites as robust print coatings on textile fabric alters the percolation threshold, strain‐reversible piezoresistivity is retained, confirming that they are suitable as printable strain sensors.     

Fabrication of CdSe‐Nanofibers with Potential for Biomedical Applications

The design and synthesis of nanostructured functional hybrid biomaterials are essential for the next generation of advanced diagnostics and the treatment of disease. A simple route to fabricate semiconductor nanofibers by self‐assembled, elastin‐like polymer (ELP)‐templated semiconductor nanoparticles is reported. Core–shell nanostructures of CdSe nanoparticles with a shell of ELPs are used as building blocks to fabricate functional one‐dimensional (1D) nanostructures. The CdSe particles are generated in situ within the ELP matrix at room temperature. The ELP controls the size and the size‐distribution of the CdSe nanoparticles in an aqueous medium and simultaneously directs the self‐assembly of core–shell building blocks into fibril architectures. It was found that the self‐assembly of core–shell building blocks into nanofibers is strongly dependent on the pH value of the medium. Results of cytotoxicity and antiproliferation of the CdSe‐ELP nanofibers demonstrate that the CdSe‐ELP does not exhibit any toxicity towards B14 cells. Moreover, these are found to be markedly capable of crossing the cell membrane of B14. In contrast, unmodified CdSe nanoparticles with ELPs cause a strong toxic response and reduction in the cell proliferation. This concept is valid for the fabrication of a variety of metallic and semiconductor 1D‐architectures. Therefore, it is believed that these could be used not only for biomedical purposes but for application in a wide range of advanced miniaturized devices.     

Stretchable and Heat‐Resistant Protein‐Based Electronic Skin for Human Thermoregulation

Silk protein is one of the a promising materials for on‐skin and implantable electronic devices due to its biodegradability and biocompatibility. However, its intrinsic brittleness as well as poor thermal stability limits its applications. In this work, robust and heat‐resistant silk fibroin composite membranes (SFCMs) are synthesized by mesoscopic doping of regenerated silk fibroin (SF) via the strong interactions between SF and polyurethane. Surprisingly, the obtained SFCMs can endure the tensile test (>200%) and thermal treatment (up to 160 °C). Attributed to these advantages, traditional micromachining techniques, such as inkjet printing, can be carried out to print flexible circuits on such protein substrate. Based on this, Ag nanofibers (NFs) and Pt NFs networks are successfully constructed on both sides of the SFCMs to function as heaters and temperature sensors, respectively. Furthermore, the integrated protein‐based electronic skin (PBES) exhibits high thermal stability and temperature sensitivity (0.205% °C^?1). Heating and temperature distribution detection are realized by array‐type PBES, contributing to potential applications in dredging of the blood vessel for alleviating arthritis. This PBES is also inflammation‐free and air‐permeable so that it can directly be laminated onto human skin for long‐term thermal management.     

3D2 Self‐Assembling Janus Peptide Dendrimers with Tailorable Supermultivalency

The self‐assembly of peptides enables the construction of self‐assembled peptide nanostructures (SPNs) with chemical composition similar to those of natural proteins; however, the structural complexity and functional properties of SPNs are far beneath those of natural proteins. One of the most fundamental challenges in fabricating more elaborate SPNs lies in developing building blocks that are simultaneously more complex and relatively easy to synthesize. Here, the development of self‐assembling Janus peptide dendrimers (JPDs) is reported, which have fully 3D structures similar to those of globular proteins. For the reliable and convenient synthesis of JPDs, a solid‐phase bifurcation synthesis method is devised. The self‐assembly behavior of JPDs is unique because only the dendrimer generation and not the weight fraction dictates the morphology of SPNs. The coassembly of two JPD building blocks provides an opportunity not only to enlarge the morphological repertoire in a predictable manner but also to discover SPNs with unusual and interesting morphologies. Because JPD assemblies have dual multivalency, i.e., supramolecular and unimolecular multivalency, the JPD system enables the statistical selection of materials with high avidity for the desired cell types and possibly any target receptors.     

Janus Microcarriers for Magnetic Field‐Controlled Combination Chemotherapy of Hepatocellular Carcinoma

Combination chemotherapy administering multiple chemo agents is widely exploited for the treatment of various cancers in the clinic. Specially for hepatocellular carcinoma (HCC), one of the most common malignancies, a coadministration of combinational cytostatic multikinase inhibitors and cytotoxic chemo agents has been suggested as a potential curative approach. Here, Janus microcarriers are developed for the controlled local combination chemotherapy of HCC. The Janus microcarriers are composed of a polycaprolactone (PCL) compartment and a magnetic nanoparticle‐loaded poly(lactide‐co‐glycolic acid) (PLGA) compartment which contains hydrophobic regorafenib and hydrophilic doxorubicin, respectively. Exploiting the magnetic anisotropy, rotational motion of the Janus microcarriers is controlled with a magnetic field, which enables the active corelease of dual chemo agents. Furthermore, Janus microcarriers exhibit magnetic resonance (MR) contrast effect, supporting the successful transcatheter intra‐arterial delivery of the combination chemo agents loaded in the microcarriers to the targeted tumor. This Janus microcarrier potentially serves as a general combinational chemotherapeutic platform for the codelivery of various combinations of multichemo agents.     

Mussel‐Inspired Electrospun Smart Magnetic Nanofibers for Hyperthermic Chemotherapy

A method for the versatile synthesis of novel, mussel‐inspired, electrospun nanofibers with catechol moieties is reported. These mussel‐inspired nanofibers are used to bind iron oxide nanoparticles (IONPs) and the borate‐containing anticancer drug Bortezomib (BTZ) through a catechol metal binding mechanism adapted from nature. These smart nanofibers exhibit a unique conjugation of Bortezomib to their 1, 2‐benzenediol (catechol) moieties for enabling a pH‐dependent drug delivery towards the cancer cells and the IONPs via strong coordination bonds for exploiting the repeated application of hyperthermia. Thus the synergistic anticancer effect of these mussel‐inspired magnetic nanofibers were tested in vitro for the repeated application of hyperthermia along with the chemotherapy and found that the drug‐bound catecholic magnetic nanofibers exhibited excellent therapeutic efficacy for potential anticancer treatment.     

Strain Engineering of Wave‐like Nanofibers for Dynamically Switchable Adhesive/Repulsive Surfaces

Engineering surfaces that enable the dynamic tuning of their wetting state is critical to many applications including integrated microfluidics systems, flexible electronics, and smart fabrics. Despite extensive progress, most of the switchable surfaces reported are based on ordered structures that suffer from poor scalability and high fabrication costs. Here, a robust and facile bottom‐up approach is demonstrated that allows for the dynamical and reversible switching between lotus leaf (repulsive) and rose petal (adhesive) states by strain engineering of wave‐like nanofiber layers. Interestingly, it is found that the controlled switching between these two distinctive states is sensitive to the shape of the nanofibers. Moreover, it is observed that the structural integrity of the nanofibers is fully preserved during multicycle dynamic switching. The application of these optimal structures is showcased as mechanical hands demonstrating the capture of water microdroplets and their subsequent release in a well‐controlled manner. It is envisioned that this low‐cost and highly scalable surface texture is a powerful platform for the design of portable microfluidics systems, and the fabrication of large‐scale devices for ambient humidity harvesting and water purification.     

Iron Fluoride–Carbon Nanocomposite Nanofibers as Free‐Standing Cathodes for High‐Energy Lithium Batteries

The development of low‐cost, high‐energy cathodes from nontoxic, broadly available resources is a big challenge for the next‐generation rechargeable lithium or lithium‐ion batteries. As a promising alternative to traditional intercalation‐type chemistries, conversion‐type metal fluorides offer much higher theoretical capacity and energy density than conventional cathodes. Unfortunately, these still suffer from irreversible structural degradation and rapid capacity fading upon cycling. To address these challenges, here a versatile and effective strategy is harnessed for the development of metal fluoride–carbon (C) nanocomposite nanofibers as flexible, free‐standing cathodes. By taking iron trifluoride (FeF₃) as a successful example, assembled FeF₃–C/Li cells with a high reversible FeF₃ capacity of 550 mAh g^?1 at 100 mA g^?1 (three times that of traditional cathodes, such as lithium cobalt oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese oxide) and excellent stability (400+ cycles with little‐to‐no degradation) are demonstrated. The promising characteristics can be attributed to the nanoconfinement of FeF₃ nanoparticles, which minimizes the segregation of Fe and LiF upon cycling, the robustness of the electrically conductive C network and the prevention of undesirable reactions between the active material and the liquid electrolyte using the composite design and electrolyte selection.     

Interference‐aware convergecast scheduling in wireless sensor/actuator networks for active airflow control applications

Emerging wireless sensor/actuator network (WSAN) technology has the potential to enable semi‐autonomous airflow control to improve the aerodynamic performance of aircraft. In this paper, a WSAN comprising of multiple linear sensor clusters terminated by actuators is proposed for active airflow control with the objective of minimizing convergecast latency. Here, the convergecast delay is defined as the time required from the beginning of a sampling period to all all sensor's data of this sampling period is received by the actuator. The objective is achieved by minimizing the separation distance of concurrent data transmission so that the number of nodes sending data in the same time slot is maximized. The problem turns into a scheduling problem with a proper selection of interference separation. However, most existing work on the scheduling in linear networks use the minimum separation of two hops to avoid collisions. This paper examines the relationship between the hop separation, signal‐to‐noise ratio, and the latency to make a selection of interference separation. A new interference aware hybrid line scheduling (HLS) algorithm is proposed and its energy consumption is analyzed. Compared with other line scheduling policies, the analysis and simulation results show that, at moderately high node densities, the proposed HLS with carefully selected hop separation is able to reduce both the delay by up to 15% and the energy consumption somehow. Copyright © 2012 John Wiley & Sons, Ltd.