FOR SELF-CHARGING POWER, PROOF IS IN THE PAPER Although batteries currently power most portable electronics, these are usually the largest or heaviest component of each device and have significant drawbacks, such as the need to be charged or replaced frequently. Thus, finding new self-sustaining power sources is important for supporting portable electronics’ burgeoning growth. Triboelectric nanogenerators (TENGs), which couple triboelectrificaiton and electrostatic induction, have attracted attention for their ability to harvest mechanical energy efficiently. By attaching supercapacitors to these devices, researchers have created consolidated self-charging power units (SCPUs). However, most of these devices have used acrylic substrates, leading to relatively large and heavy devices. In a recent study, Guo et al. (DOI: 10.1021/acsnano.7b00866) looked to paper substrates for their SCPUs. The researchers created sandpaper-based supercapacitors with a conductive Au layer and a graphite coating as the active layer. They then attached these supercapacitors to a rhombic-shaped TENG composed of hard paper that was coated with nanostructured fluorinated ethylene propylene and Au and cut into pieces that integrated into complete units. Tests showed that when mechanical force was repeatedly applied, the TENG could charge the supercapacitor within minutes. Small enough to fit into a wallet, this SCPU could effectively run a wireless remote, an electric watch, and a temperature sensor. The authors suggest that this cut-paper device has potential as a sustainable power source for a variety of portable practical and medical applications.
accomplished only with ensemble methods that use fluorescently labeled ubiquitin or substrates, a method that cannot monitor the cascade of enzymes necessary for this process and might alter the kinetics and efficiency of the ubiquination reaction. In a recent study, Wloka et al. (DOI: 10.1021/ acsnano.6b07760) devised a method to monitor ubiquination in a fast, single-molecule, and label-free way. Their method relies on an engineered version of the biological nanopore Cytolysin A (ClyA) and the ubiquitin-conjugating protein Ubc4 from Saccharomyces cerevisae, which can ubiquinate itself in vivo. By adding Ubc4 to the cis side of the nanopore, either in purified, monoubiquinated, or polyubiquinated forms, and then monitoring the ionic currents, the researchers found that they could distinguish between these three varieties by differences in the individual current blockades. In addition, by modifying Ubc4 to enable precise placement of ubiquitin on any of three potential ubiquination sites, the researchers showed that it was possible to discriminate between different monoubiquinated isomers. Finally, they show that following changes in ionic current enables monitoring the ubiquination cascade in real time. The authors suggest that using nanopores could accelerate the understanding of the mechanisms behind ubiquination.
NANOPARTICLES SEEK AND DESTROY METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS Methicillin-resistant Staphylococcus aureus (MRSA) remains an urgent public health concern, accounting for numerous cases of morbidity and mortality annually. Sensitively diagnosing and treating infections caused by these drug-resistant bacteria at an early stage can greatly reduce these risks. Optical imaging based on activatable fluorescent probes, such as those that use florescence resonance energy transfer (FRET), offers one way to diagnose infection in vivo. However, the FRET probes developed thus far depend on a limited number of bacterial enzymes and usually require a complicated chemical design and synthesis process. In a recent study, Zhao et al. (DOI: 10.1021/ acsnano.7b00041) report an alternate strategy that uses probes that are able both to detect and to kill MRSA using photothermal therapy. These probes are composed of silica nanoparticles loaded with vancomycin-modified polyelectrolyte−cypate complexes. Because hydrophobic cypate, a cyanine dye, tends to
GETTING THE HOLE STORY ON UBIQUITINATION Ubiquination, the post-translational modification that involves covalently attaching the small protein ubiquitin to a larger substrate protein, is important in a variety of biological processes. This event can prompt protein degradation, the movement of proteins to different cellular locations, or the inhibition of protein interactions, and abnormal ubiquination has been linked to disease. Currently, monitoring ubiquination in vitro has been © 2017 American Chemical Society
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aggregate on the nanoparticles in aqueous environments, the probes remain nonfluorescent until they encounter MRSA. In vitro tests show that these bacteria can partly dissociate the polyelectrolyte from the nanoparticles, leading to near-infrared fluorescence. Microscopy showed that following up with photothermal therapy disrupted the bacterial cell wall and membrane, leading to cell death. In vivo experiments in mouse models showed that these nanoparticles could be used to diagnose MRSA infections in animals with either surface or deep tissue infections and treat them, leading to faster healing than mice treated with different methods. The authors suggest that the strategy outlined in this study might be used to combat a variety of other drug-resistant bacterial infections.
KNOCK, KNOCK: WATCHING INFLUENZA GAIN ENTRY INTO CELLS Influenza A virus (IAV) remains one of the most hazardous global public health threats, responsible for considerable morbidity and mortality each year. Although it has been established that the first step in IAV infection is for the virus to attach to a host cell by its major envelope protein, hemagglutinin, other events that lead to endocytosis are not well understood. For example, although most endocytosis of this virus is thought to be clathrin-mediated, several studies have also suggested a clathrin-independent route for infection. How this second pathway might work, as well as other proteins involved in both routes, are largely unknown. To understand IAV endocytosis, Sun et al. (DOI: 10.1021/ acsnano.6b07853) used fluorescence microscopy-based singlevirus tracking to visualize viral entry into cells. After biotinylating IAV viral envelopes, the researchers attached streptavidinquantum dots (SA-QDs). Clathrin and dynamin proteins were also fluorescently labeled. Using these tools, the researchers found that the majority of entry events are clathrin-dependent, with clathrin and dynamin recruited asynchronously. Dynamin appears to be important for maturation of the clathrin-coated pit. However, the majority of entry events through this route are abortive. Alternatively, experiments further supported a clathrinindependent route for viral endocytosis. Dynamin was also critical for this type of entry; using two different dynamin inhibitors, the researchers showed that viral endocytosis in either route cannot proceed. The authors suggest that using QDs to track viruses can reveal even more details about viral entry and other processes in cells.
SHINING A NEW LIGHT ON CANCER THERAPY Photodynamic therapy (PDT), which uses photosensitizers to generate reactive oxygen species (ROS) under light irradiation, can kill cancer cells both directly and indirectly. In addition to the tumor cells killed by exposure to ROS, the generated tumor cell residues can promote antitumor immune responses. However, PDT has prominent drawbacks. For example, conventional photosensitizers used for this purpose are typically excited by visible light, which has limited tissue penetration and cannot reach deep-seated tumors. Moreover, the immune stimulating effect is not strong enough to inhibit significantly the growth of tumor cells left behind after PDT. To combat these drawbacks, Xu et al. (DOI: 10.1021/ acsnano.7b00715) developed a multicomponent method to improve tissue penetration and to boost immune response. This view on upconversion nanoparticles converts long-wavelength near-infrared light, which penetrates tissues more deeply, into the short-wavelength light necessary for stimulating photosensitizers. The authors coloaded these nanoparticles with the photosensitizer chlorin e6 and imiquimod, a Toll-like-receptor7 agonist that serves as an immune adjuvant. These particles stimulated both cellular destruction and immune stimulation in vitro. By combining this treatment with a CTLA-4 blockade, a checkpoint inhibitor that removes a negative regulator to cancerfighting immune cells, the researchers show complete elimination of primary tumors and strong inhibition of distant tumors. Furthermore, rechallenging treated mice with a second inoculation of cancer cells resulted in further tumor inhibition, suggesting long-term immune memory. The authors suggest that this combination method shows significant potential for fighting cancer and preventing recurrence. 4378
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THE AMAZING TECHNICOLOR NANODISKS People have long manipulated the interactions between light and matter to influence the color of objects, often through the localized surface plasmon resonances of metallic nanoparticles. The optical qualities of these materials can be tuned by changing the nanoparticles’ size, shape, arrangement, or material. This effect has attracted attention recently for potential uses of nanoparticles in high-resolution, high-fidelity, or ultrathin color displays. However, results thus far have been disappointing, with plasmonic nanostructures having low color saturation and brightness. Various methods have been used to improve these parameters, including a Fabry−Perot cavity with multilayer films, guided mode resonances, or gratings, but these methods are not suitable for ultrasmall pixel design. In a recent study, Wang et al. (DOI: 10.1021/ acsnano.6b08465) tested a different approach for generating highly saturated and bright colors: metal−insulator−metal sandwich nanodisks that enhance in-phase electric dipole modes that are blue-shifted compared to nanodisks composed only of metal. This tweak enables relatively large nanodisks, which are significantly easier to synthesize than small ones, to generate short wavelength colors. Using nanodisks made of an aluminum oxide layer between two silver layers, the researchers realized vivid red-green-blue colors in reflection and cyanmagenta-yellow colors in transmission as a result of hybridization between Wood’s anomaly and the in-phase electric dipole modes. By changing the radius of the nanodisks and the period of each array, the researchers were able to generate 16 samples of different colors. The authors suggest that this method can be used to generate bright, saturated colors for use in imaging, data storage, ultrafine displays, and plasmon-based biosensors.
substrates using the same method but altered variables to better understand their roles. After varying the pressures of precursor gases SiH4, PH3, HCl, and Au catalysts, the researchers found that NW growth in the ⟨111⟩ direction was unstable at high SiH4 partial pressures and growth rates, but HCl can stabilize growth through chlorination of the NW sidewall. In addition, Au deposited on the NW surface aggregates and can impede wet etching by KOH but not by buffered HF. However, this effect can be mitigated by increasing the SiH4 partial pressure and the NW growth rate. Taking these findings into consideration, the researchers were able to realize several complex and arbitrary Si NW morphologies. The authors suggest that being able to control the parameters used in this method precisely could lead to specifically designed morphologies necessary for a variety of electronic and photonic applications.
TRUE COLORS SHINE THROUGH WITH TIO2 METASURFACES Instead of pigments that absorb some wavelengths of light and scatter others or light sources that directly produce particular wavelengths, structural coloration uses nanostructures to separate different colors through scattering, diffraction, and material dispersion. The natural world has a myriad of examples of this phenomenon, including peacock feathers, butterfly wings, opals, and pearl oyster shells. Synthetic versions of structural coloration have been generated with the plasmonic resonances of metallic nanoparticles; however, the colors produced through this method are not always distinct and have low spatial resolution. Seeking a way around these drawbacks, Sun et al. (DOI: 10.1021/acsnano.7b00415) developed TiO2 metasurfaces to generate structural coloration through electric and magnetic resonances. The researchers fabricated these materials using electron-beam lithography on an ITO-coated glass substrate, onto which a TiO2 film was deposited. The resulting nanostructures have square bases extending into trapezoids in the vertical direction. By changing the unit sizes of this design, the researchers created 88 samples that produce a range of distinct colors representing the entire visible spectrum with a spatial resolution down to 16000 dpi. Using the parameters discovered in these samples, the researchers used these TiO2 metasurfaces to generate arbitrary colors, creating a full color image of their university logo. The authors suggest that these findings could eventually be used for applications such as optical displays, imaging, data storage, and color filters with high contrast and brightness.
NEW MORPHOLOGIES FOR VERTICALLY ALIGNED SEMICONDUCTOR NANOWIRES Vertically aligned semiconductor nanowires (NWs) with various morphologies have been explored for a variety of applications. For example, those with a constriction have potential as resistive memory elements, and those with periodic grating have optical filtering capabilities. Recently, researchers were able to encode precise sub-10 nm morphology in Si NWs grown using a process that combined phosphorus doping with dopant-dependent wet etching. However, the part that each variable plays in controlling the outcome of this process was unclear. In a recent study, the same team of Kim et al. (DOI: 10.1021/ acsnano.7b00457) grew ⟨111⟩ epitaxial Si NWs on (111) Si 4379
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MXENE AND MATCHING: PREDICTING NEW DOUBLE-TRANSITION-METAL MXENES The extraordinary properties of many two-dimensional (2D) materials, including graphene and transition metal dichalcogenides, have generated intense interest in discovering more of these materials. One recently discovered class is MXenes, 2D layered transition metal carbides and/or nitrides derived mostly by selective etching of A-element layers from their parent ternary carbides and nitrides, known as MAX phases. MXenes are electrically conductive and hydrophilic, qualities that give them potential for applications in batteries and supercapacitors, electromagnetic interference shielding, electrocatalysis, and as topological insulators. About 20 materials in this class have been synthesized to date, but only a few of these are double-transitionmetal MXenes. As a first step to designing more, assessing the relative stability of different structural possibilities will be key. However, covering the entire field of possibilities is impossible experimentally. In a recent study, Tan et al. (DOI: 10.1021/acsnano.6b08227) used high-throughput computation to evaluate the structure− stability relationships for over a million possibilities of undiscovered double-transition-metal MXenes. The researchers focus on eight selected types of alloys: (V1−xMox)3C2, (Nb1−xMox)3C2, (Ta1−xMox)3C2, (Ti1−xMox)3C2, (Ti1−xNbx)3C2, (Ti1−xTax)3C2, (Ti1−xVx)3C2, and (Nb1−xVx)3C2, with 0 ≤ x ≤ 1. Combining first-principles density functional theory calculations with the cluster expansion method, the researchers found potential for ordered configurations in Moand Ti-rich MXenes, with ordering increasing after postsynthesis annealing. However, alloying Ti with V results in solid solutions across all compositions, and (Nb1−xVx)3C2 phase separates at lower temperatures and forms solid solutions at higher ones. The authors suggest that these predictions can guide synthesis of multielement MXene alloys in the future.
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