FULLY EXTENDABLE TRIBOELECTRIC YARNS? NOT A STRETCH The field of wearable electronics has undergone rapid growth over the past several years, necessitating wearable energy sources. Although lithium-ion batteries have successfully been used to power many portable electronics, they are not suitable for wearable electronics due to their limited capacity and low flexibility, stretchability, and biocompatibility. One alternative is harvesting the “wasted” biomechanical energy from human motion to power these devices. To that end, several research groups have investigated the use of triboelectric nanogenerators (TENGs) to power wearable electronics. However, the TENGs developed thus far suffer from low stretchability, durability, and suboptimal output. To address these challenges, Kwak et al. (DOI: 10.1021/ acsnano.7b05203) developed a fully stretchable, high performance TENG (s-TENG) made of strong, knitted materials that are already available in the textile industry. The researchers fabricated their s-TENG using knitted polytetrafluoroethylene (PTFE) and Ag as the negative and neutral triboelectric materials with an Ag electrode in the middle. Using three different weaves commonly used in the textile industry (plain knit, double knit, and rib knit), the researchers investigated differences in morphology, roughness, density, and stretchability on triboelectric performance. Tests showed that the rib knit fabric had the highest contact area and stretchability, which both translated into a higher generation of triboelectric charges upon stretching and releasing. As proof of principle, the output voltage of this fabric was used to illuminate green LEDs when integrated into sportswear that a volunteer wore while running. The authors suggest the feasibility of stretchable knitted TENGs for harvesting energy from human motion.
To improve on these techniques, Liu et al. (DOI: 10.1021/ acsnano.7b04878) designed and implemented a new tool they named the exosome total isolation chip, or ExoTIC. ExoTIC uses a simple filtration process in which fluids including culture media, plasma, and urine, are passed through a polycarbonate track-etched nanoporous filter membrane. While free nucleic acids, proteins, lipids, and other small fragments are flushed out, concentrated extracellular vesicles can be collected from the filter membrane using a standard pipet. Tests showed that this method resulted in significantly higher exosome yields from culture media and clinical samples than ultracentrifugation and PEG precipitation. The researchers also show that ExoTIC could sort extracellular vesicles by size using different filters. Comparing the microRNA and proteomic profiles of collected vesicles showed that results from ExoTIC were on par with ultracentrifugation. The authors suggest that this platform’s ability to extract exosomes from a broad array of complex biofluids could be applied to cancer and a wide range of infectious diseases.
LITHIUM-ION BATTERIES HIT THE ASPHALT Lithium-ion batteries (LIBs) have fueled the rise of portable electronics. Of available anode materials, Li metal has proven to be an excellent candidate. However, the charging process promotes the formation of Li dendrites, branching strands of Li that damage the cycling performance of the anode and increase the risk of fires. One strategy to suppress dendrite formation is to use a conductive host material on which Li can deposit uniformly. Host materials including hexagonal unstacked graphene, sparked reduced graphene oxide, and copper nanowire networks have recently shown promise. However, synthesizing these materials can be complicated, timeconsuming, or expensive, restricting their large-scale application. Wang et al. (DOI: 10.1021/acsnano.7b05874) report a simpler and cheaper solution to this problem: using glisonite, a naturally occurring, porous carbon with an ultrahigh surface area generated from asphalt. After activating this material with KOH, the researchers improved its conductivity by mixing it with graphene nanoribbons. They then tested the performance of this material in coin cells in which this anode was coated with Li through electrochemical deposition and surrounded by a concentrated electrolyte. Experiments showed that this material had high rate performance and Coulombic efficiencies.
AN EXOTIC SOLUTION TO EXOSOME ISOLATION Exosomes, nanometer-sized vesicles that are actively shed from cells into body fluids, have emerged as promising biomarkers for detecting cancers, following the progression and effects of treatments, and predicting outcomes. However, the lack of tools to isolate intact exosomes consistently with high yields and purity has stymied this field. Currently, the best way to isolate exosomes is through ultracentrifugation; however, this method is labor intensive, time-consuming, and can result in poor exosome quality. Alternative methods, such as polyethylene glycol (PEG) precipitation, are cumbersome, expensive, and slow. © 2017 American Chemical Society
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It was also stable for more than 500 cycles and demonstrated a high area capacity at a discharge/charging rate that was ten times faster than that of typical LIBs. Full batteries built with these anodes had both high power density and high energy density. The authors suggest that this material could offer an inexpensive option for ultrafast charging without compromising long-term performance.
A WELL-ROUNDED WAY TO MAKE SINGLE-MODE LASERS Semiconductor lasers oscillating at a single frequency, such as single-mode lasers, have promise for use in on-chip optical processing, communications, and data storage. However, most reported thus far are subject to random fluctuations and instabilities because they lack a mode selection mechanism. One way to obtain a single-mode laser is to reduce the optical path of the laser cavity to keep only one mode surviving in the bandwidth of the optical gain. However, reducing the cavity size also usually increases optical loss, resulting in high thresholds and low cavity quality factors for lasing action. To avoid these issues, Tang et al. (DOI: 10.1021/ acsnano.7b04496) developed single-mode lasers based on cesium lead halide perovskite submicron spheres, a material with high optical gain and good optical confinement. Their success relies on both the high gain nature of the material as well as the perfectly spherical shape of these particles, leading to whispering gallery resonant modes. The researchers synthesized these spheres using a simple chemical vapor deposition method, then tested them in optically pumped laser experiments. Results showed that these materials could be used to form single-mode lasers with a narrow line width, low threshold, and high-cavity quality factor. Further experiments showed that altering the halide composition and size of the spheres could tune the laser’s wavelength throughout the visual spectrum from red to violet. The authors suggest that this work offers a way to produce a widely tunable and miniaturized single-mode laser.
MAGNETOSOMES MASQUERADE AS ANTIGEN-PRESENTING CELLS Immunotherapy is a burgeoning category of cancer-fighting modalities that turn a patient’s own immune system against the disease. These strategies are highly dependent on the efficient stimulation of antigen-specific immune cells. One of these therapies, known as adoptive T-cell transfer, involves isolating and expanding autologous T cells while simultaneously stimulating them with antigen-presenting cells, particularly dendritic cells. These cytotoxic T cells (CTLs) are then reinfused into the cancer patient to elicit an antitumor response. Although promising, this strategy has several drawbacks, including taking several months to perform, exhibiting poor reproducibility due to dendritic cell variability, and poor survival and unpredictable paths of the CTLs, limiting their therapeutic effect. Seeking a way around these problems, Zhang et al. (DOI: 10.1021/acsnano.7b04955) developed a platform that uses magnetic nanoclusters to mimic antigen-presenting cells, not only to expand and to stimulate CTLs but also to guide them to tumor tissues visually. The researchers used a hydrothermal technique to construct magnetic nanoclusters out of many smaller units, creating resulting particles that were both superparamagnetic and magnetic. These particles were then coated with azide-engineered leukocyte membranes and decorated with T-cell stimuli using mild and efficient copperfree click chemistry. These nano artificial antigen-presenting cells demonstrated that they could successfully be used to expand and to stimulate T cells, and their magnetic and superparamagnetic features could be used to guide them to tumors in vivo with a magnetic field while visualizing them with magnetic resonance imaging. The resulting CTLs delayed tumor growth in a murine lymphoma model. The authors suggest that this platform shows promise in cancer immunotherapy.
TRAP AN ATOM, CHANGE A FUNCTION One way to develop nanoscale components with desired functionality is by manipulating individual atoms and molecules. The probe tip of a scanning tunneling microscope 10634
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record-high quality factor of 1011. The researchers explore these resonance modes with finite difference time domain simulations, with results supporting experimental findings. The authors suggest that these results illustrate the promise of light emitters based on all-dielectric metasurfaces for devices such as lasers and modulators.
can be used to accomplish this goal, with organic molecules serving as traps for single adatoms. Researchers have used this technique to control the electronic spectrum of a molecule by doping or bond formation, to trap and to drive atoms, or to confine a molecular motion to rotation during manipulation. Pham et al. (DOI: 10.1021/acsnano.7b05235) go a step further, achieving each of these functionalities in a single system. The researchers accomplish this feat by combining a gold adatom on a Au(111) surface with a tetraphenylporphorin molecule (H2TPP) that contains three types of trapping sites: phenyl groups; pyrrole groups; and the center of the macrocycle pointed by four nitrogen atoms, two of which are hydrogenated. Their experiments show that atom trapping on a phenyl or pyrrole group leads to electron doping of the molecule. Trapping the adatom at the macrocycle center along tip-induced single deprotonation leads the molecule to rotate; a second deprotonation leads to a molecular jumper, with translation and rotation under voltage pulse excitation. Density functional theory calculations add insight into the mechanisms behind these findings. Further experiments show that more complicated combinations are possible, with a second adatom being used to design a rotor with an off-centered axis. The authors suggest that the atom-trapping chemistry illustrated in this study could be used for bottom-up design to create molecules with desired functionalities.
THE MAKING OF A META-ARYNE Arynes are important intermediates for a variety of different types of synthesis reactions. Recent studies have shown that these species can be generated on surfaces from dihalogenated aromatic precursors by cleaving two C−X bonds, where X = Br or I. Generating arynes from physisorbed diiodobenzene precursor molecules on metal surfaces causes them to form bonds to the metal, but these products are stabilized on insulating surfaces. The character of the resulting meta-arynes remains controversial; whereas some reports have concluded that they have a diradical structure, others suggest an anti-Bredt olefin structure. To clarify this issue, Pavliček et al. (DOI: 10.1021/ acsnano.7b06137) took advantage of the different behaviors of arynes on metals and insulators by generating meta-arynes on both the more reactive Cu(111) surface and the relatively inert NaCl surface. Starting with a precursor, the researchers applied a pulse to break the two C−I bonds. Results show significant differences between the meta-arynes generated on the two surfaces. For example, the threshold voltage to cleave the C−I bonds was significantly lower on the NaCl surface compared to the Cu(111) surface. Whereas the meta-aryne formed on the Cu(111) surface was tilted due to bond formation with the metal, the product formed on the NaCl surface was planar, enabling it to be readily visualized with atomic force microscopy. This molecule had a diradical structure, rather than an anti-Bredt olefin one. The authors suggest that in addition to helping solve a fundamental question, these findings could be useful for designing onsurface transformations based on meta-aryne intermediates.
A BRIGHT FUTURE FOR PHOTOLUMINESCENCE ENHANCEMENT Enhancing light−matter interactions with metallic nanoparticles and nanostructures has a variety of applications in fields including lasing, nonlinear optical processes, and enhanced light emission. However, strong dissipative metal losses accompany the optical response in these structures, which compromises their performance. To compensate for this loss, significant efforts have focused on using gain materials. Recent research suggests that all-dielectric materials have significant potential for light emitters due to their strong electric and magnetic resonances, with negligible loss at wavelengths above the material bandgap. Yuan et al. (DOI: 10.1021/acsnano.7b04810) pursue this strategy, reporting an all-dielectric asymmetric metasurface structure that exhibits strong photoluminescent enhancement. This metasurface consists of a periodic lattice of asymmetric air holes, in the shape of a combined semicircle and semiellipse, in a silicon-on-insulator slab embedded with four layers of selfassembled Ge quantum dots (QDs). When the QDs are pumped by an external light source, their light emission excites collective oscillations of displacement currents in the metasurface. These displacement currents interfere destructively, eventually leading to Fano resonances. The reinforcement of this resonance behavior from the identical unit cells enhances the photoluminescence of the QDs more than 1000-fold, with a
UNDERSTANDING INTERACTIONS BETWEEN SINGLE-MOLECULE MAGNETS Single-molecule magnets (SMMs) have attracted increasing attention as promising candidates for encoding information in 10635
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single, identical units. Among these, the TbPc2 double-decker molecule, a type of mononuclear bis(phthalocyaninato)lanthanide(III) complex, has been the most investigated mononuclear SMM in recent years. In addition to its high magnetic antisotropy barrier, slow relaxation time of the magnetization, robustness, and evaporability, studies have suggested that its unique spin characteristics could be exploited in quantum computing. Despite significant advances in understanding SMMs over the past decade, much remains unknown about the effects of the environment on the magnetic properties of these unusual molecules, particularly how they operate in groups. Amokrane et al. (DOI: 10.1021/acsnano.7b05804) help to answer this question by examining the role of the unpaired radical electron in the top ligand of TbPc2 by comparing the spectroscopic features of these SMMs either when isolated or in two-dimensional (2D) assemblies on surfaces. Their findings suggest that the presence or absence of Kondo resonance in dI/ dV maps is a good determinant of the lateral interaction between molecules in 2D networks. High-resolution scanning tunneling microscopy showed that π-orbital lobes linked through orbital overlap have paired-up electron wave function, and thus do not have Kondo resonance. Consequently, small clusters built through molecular manipulation show alternating Kondo features of quantum mechanical origin. However, when these SMMs form extended domains, a geometric rearrangement occurs that causes the quenching of the Kondo signal on one lobe of each pair. The authors suggest that these results could help in designing and engineering chemically tailored molecules with desired electronic structure and magnetic behavior.
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