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A NANOPRINT DISPLAY OF A DIFFERENT COLOR Researchers have sought to capitalize on the nanostructurebased light−matter interactions known as extrinsic structural colors to create displays. However, this color nanoprinting only works statically, limiting advanced applications such as anticounterfeiting, dynamic full-color displays, and high-security encryption. Photoluminescent materials, which produce intrinsic emission color, can also be used for generating color. However, although emission peaks can be tuned with anion exchange, the color variation is too slow and cannot be controlled in situ, rendering these materials unsuitable for dynamic displays. Capitalizing on the strengths of both extrinsic and intrinsic color, Gao et al. (DOI: 10.1021/acsnano.8b02425) combined these phenomena into a single in situ reversible color nanoimprinting paradigm. The researchers created gratings of methylammonium lead halide perovskite (MAPbX, where MA = CH3NH3+ and X = Cl, Br, I, or their mixture). Varying the period and gap of these gratings produces different structural colors when they scatter white light. In addition, the MAPbX, a photoluminescent semiconductor, produces emission color when stimulated with a laser. Using both light sources, these extrinsic and intrinsic colors can mix to create additional colors that are tunable over a large range with transitions on the nanosecond time scale. The investigators used this concept to create a dynamic color image of their institution’s logo as a proof of concept. The authors suggest that this interplay between structural and emission color can promote advances in classified nanoimprinting, augmented reality devices, biosensing, and other applications.
extremely high temperatures, rendering the process harsh, expensive, and energy intensive. Seeking a way to achieve the same effect at ambient temperatures, Zhang et al. (DOI: 10.1021/acsnano.8b04322) developed bioinspired graphene-based nanocomposite fibers (BGNFs) using design principles originating from nacre. The researchers created GO-Ca2+ fibers by wet-spinning GO suspensions with a coagulation bath of calcium chloride solution, introducing ionic bonding. After reducing in HI, π−π interactions between reduced GO sheets were induced by successively immersing these fibers into a N-hydroxysuccinimide ester/dimethylformamide solution and a 1-aminopyrene/ dimethylformamide solution. These synergistic interfacial interactions endowed the fibers with a toughness of up to 18.7 MJ m−3, a record value for graphene fibers fabricated under ambient temperature. They also retained high electrical conductivity, even after thousands of cycles of loading− unloading testing. The authors suggest that these qualities make the BGNFs promising candidates for applications in flexible and stable electrical devices, such as strain sensors and actuators.
NANOPARTICLE THERAPY GOES ORAL Nanomedicine therapeutic and diagnostic products have made headway in a variety of diseases. Thus far, these formulations have predominantly been successful with intravenous administration, with some limited nasal and pulmonary delivery. Despite the attractive nature of oral administration, researchers have yet to create formulations successful at significant absorption of solid nanoparticles in the intestines, even with numerous published attempts at different designs. Gaining access to the bloodstream through gastrointestinal absorption would thus mark a major breakthrough for nanomedicine. Kim et al. (DOI: 10.1021/acsnano.8b04315) report promising progress toward that goal by combining apical sodiumdependent bile acid transporter-mediated cellular uptake of nanoparticles with chylomicron transport pathways. The researchers functionalized the surface of commercial carboxylated polystyrene spherical nanoparticles with glycocholic acid, a bile acid that triggers the absorption of these particles into enterocytes in the distal ileum through apical sodium-dependent bile acid transporters on these cells. Tests in animal models showed that from there, the particles followed a pathway similar
IMPROVING ON NATURAL NACRE Nacre, the iridescent inner coating of some mollusk shells and the outer coating of pearls, exhibits excellent mechanical properties that combine high strength and toughness. These properties are attributed to highly structured hierarchical layers of mostly inorganic minerals with small percentages of organic materials, along with abundant synergistic interfacial interactions. In addition, nacre forms at ambient temperature. A number of recent studies have focused on graphitization of graphene oxide (GO)-based fibers to make them mechanically tough while also electrically conductive. However, although graphitization accomplishes this goal, it usually requires © 2018 American Chemical Society
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Published: September 25, 2018 8835
DOI: 10.1021/acsnano.8b06927 ACS Nano 2018, 12, 8835−8838
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Cite This: ACS Nano 2018, 12, 8835−8838
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AN ARTFUL EPIDERMAL SENSOR Significant research in the past several years has been devoted to developing electronic skins that can act as epidermal sensors, with some studies investigating the possibility of creating sensors that look like tattoos to monitor bioelectric signals. Some work has suggested that graphene grown by chemical vapor deposition (CVD) could be used as a basis for these tattoolike sensors. However, CVD graphene layers are relatively fragile, and designs require a photolithographic mask, making it difficult to obtain artistic patterns with good durability. Qiao et al. (DOI: 10.1021/acsnano.8b02162) report a process to generate graphene-based epidermal strain sensors in a body art style using laser-scribed graphene, which can grow and pattern graphene without a shield mask. The researchers created these sensors by coating graphene oxide (GO) onto a substrate, such as the wet transfer paper commonly used for temporary tattoos. Laser scribing this GO reduces it to graphene, which is left behind when the patterned material is immersed in water and then washed with a syringe. This graphene pattern can be attached to any epidermal surface, including motorial, wrinkled, or hairy skin. When packed in elastic polymer, the resulting electronic skin exhibited ultrahigh sensitivity over a large strain range and long-term stability. Monitoring changes in electrical characteristics, the researchers were able to use these sensors to detect relatively large-range movements such as finger bending, and more subtle ones such as throat movements that could be used to distinguish individual spoken words. The authors suggest that the simple process to fabricate these sensors and their artistic designs endow the devices with substantial commercial potential.
to natural fatty nanoparticles known as chylomicrons, heading to the endoplasmic reticulum and Golgi apparatus before moving to the systemic circulatory system via the lymphatic system, but avoiding a first pass to the liver. In orally dosed fasted rats, the bile acid-conjugated nanoparticles had an average oral bioavailability of 47%. The authors suggest that this simple system provides an approach for noninvasive and direct delivery of nanomedicine to the lymphatic system and systemic circulation while avoiding hepatic toxicity.
NANOTHERAPEUTICS TO SPRAY AWAY CANCER Primary cancers are often treated postoperatively by chemotherapy to destroy any remaining cancer cells. Nanomedicine formulations for chemotherapy are attractive due to the enhanced permeability and retention effect in tumors. However, even with this benefit, only 0.7% of intravenously injected nanoparticles have been reported to reach tumor sites, offering only a marginal advantage over conventional formulations. Finding a way to spray nanoparticles directly onto tumor sites could offer a way to bypass metabolic clearance; however, this method has received little attention due to the lack of nanoparticles’ underwater adhesion and difficulty with nanoparticles forming agglomerates during the spray process. Addressing both these issues, Jeong et al. (DOI: 10.1021/ acsnano.8b04533) proposed a sticky nanoparticle-based spray therapeutic system inspired by the adhesives that mussels use to attach to wet surfaces in marine environments. The researchers used an electrospraying technique to create nanoparticles loaded with the chemotherapeutic drug doxorubicin and coated with mussel adhesive proteins (MAPs). These MAP nanoparticles readily dispersed in a phosphate buffer saline/ethanol solvent and sprayed easily onto surfaces with an atomizer, exhibiting excellent adhesion on glass and porcine skin tissue, even underwater. Additional in vitro, ex vivo, and in vivo experiments showed that they released their pharmaceutical load within hours in the acid environment of tumors, significantly inhibiting tumor growth compared to free doxorubicin. The authors suggest that this system could offer a way to maximize the therapeutic effects of nanoparticle chemotherapy formulations while minimizing systemic toxicity.
SMART SCAVENGERS OF REACTIVE OXYGEN SPECIES MOP UP DENTAL DISEASE Periodontal disease is one of the most common oral diseases worldwide and the main cause of tooth loss in adults. Its primary predisposing cause is an imbalance between pathogenic bacteria and the host immune response toward this infection. As these bacteria grow into dental plaque, they release toxins. In response, immune cells release pro-inflammatory cytokines and reactive oxygen species (ROS). These ROS and other factors degrade periodontal fibers and bone, leading to serious soft- and hard-tissue destruction. Although periodontal disease can be successfully treated with methods including mechanical debridement, antibiotics, inflammatory drugs, and surgery techniques, these can involve several complicated steps and potential adverse effects. Finding more efficient ways to treat this condition, particularly the ROS production that oversteps intracellular antioxidant defense capacity, is highly desired. Bao et al. (DOI: 10.1021/acsnano.8b04022) developed a platform that uses biodegradable polydopamine nanoparticles as smart ROS scavengers in oxidative stress-induced periodontal disease. The researchers synthesized these particles via selfpolymerization at room temperature, showing that they exhibit no significant cytotoxicity even at a high concentrations. 8836
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However, tests showed that they exhibit high removal efficiency of hydroxyl and superoxide radicals in solution, as well as in in vitro models with a variety of cell types. In an animal model of periodontal disease, treatment with the polydopamine nanoparticles significantly reduced local inflammation and biodegraded within 60 days. The authors suggest that these nanoparticles hold promise for boosting antioxidant defense in periodontal disease and a wide variety of other biomedical applications.
FEEL THE VIBRATIONS: PHONON MODES OF NANOPARTICLES IN WATER Phonons in the terahertz range are the leading carrier of heat in dielectrics. Consequently, understanding the terahertz phonon dispersion and being able to tailor materials’ mesoscale structure to control phonon modes will be key for developing a whole class of thermal devices, including thermal diodes, thermoelectrics, and thermocrystals. Although a substantial body of knowledge is now available on the phonon properties of various solids and liquids, comparatively little is known about hybrid liquid and solid materials, such as colloidal suspensions. De Francesco et al. (DOI: 10.1021/acsnano.8b03101) shed some light on this phenomenon by using inelastic X-ray scattering (IXS) on a dilute suspension of Au nanospheres in water. The IXS spectra displayed features never observed in water, which the study authors were able to assign to phonon modes involving just the Au nanoparticles. However, these additional modes had a weak intensity due to the dilute nature of the suspension, making it difficult to figure out their actual number and dominant frequencies. To interpret the data, the researchers performed a thorough line shape analysis using a Bayesian inference method. Their findings enabled them to assign some inelastic features to phonon modes propagating throughout the nanoparticle interior. Surprisingly, there was no evidence in the spectra for the propagating modes that dominate the spectrum of pure water due to scattering from the sparse nanoparticles in suspension. The authors suggest that these findings might inspire ways to manipulate high-frequency acoustic propagation in hybrid liquid and solid materials.
FIGHTING MALARIA WITH A PLUG-AND-DISPLAY VACCINE Although traditional vaccines based on whole-killed or liveattenuated viruses can effectively stimulate immune responses, they also pose a risk of rare adverse events. Recombinant subunits often are not sufficiently immunogenic to progress through clinical development. One way to stimulate the immune system while reducing risk is by using self-assembling proteins as a platform for multimerization with immunogenic antigens. Such multimerization platforms are generally based on icosahedral viruses, a strategy that has led to vaccines given to millions of people. However, it has been unclear whether synthetic protein nanoassemblies that mimic the structure of these virus-like particles can show similar potency. Bruun et al. (DOI: 10.1021/acsnano.8b02805) tested this idea, leading to a synthetic multimerization platform that can elicit a high avidity antibody response against malaria antigens. The researchers started with the i301 nanocage, a porous dodecahedral 60-mer based on a protein from the hyperthermophilic bacterium Thermotoga meritima, then further altered this assembly to improve uniformity and stability. Then, to simplify conjugation to antigens, they added the protein domain known as SpyCatcher, which forms an isopeptide bond with its peptide partner SpyTag. This system can be used together for a “plug-and-display” modular assembly that separates scaffold and antigen production. After expressing this protein nanoparticle in high yields in Escherichia coli, they attached SpyTagged versions of transmission-blocking and blood-stage malaria antigens. Tests showed that these multimeric platforms prompted significantly higher antibody responses compared to monomeric antigens. The authors suggest that evaluating other computationally derived protein nanocages could lead to optimized multimerization platforms with ideal antigen spacing, number, and orientation.
CHARGING AHEAD: VISUALIZING CHARGE DENSITY DISTRIBUTIONS INSIDE ATOMS Transmission electron microscopy has become increasingly sophisticated over time, enabling sub-Angstrom imaging of crystalline lattices, the identification of single atoms, and providing information about the electronic charge density, enabling researchers to determine the chemical bonding between atoms. However, directly visualizing charged particles inside atoms remains challenging, particularly in real space. Recent advances in differential phase contrast-scanning transmission electron microscopy (DPC-STEM) bring this possi8837
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bility closer to reality. This technology measures how a subAngstrom electron probe passing through a material is affected by the atomic electric field, the field between the nucleus and the surrounding electrons. Sánchez-Santolino et al. (DOI: 10.1021/acsnano.8b03712) combine this technique with advanced electron-scattering simulations to investigate GaN, a material commonly used in optoelectronic devices. After precisely determining the specimen thickness, the researchers used this dual technique to perform a fully quantitative analysis of the atomic electric fields and charge densities. Their findings made it possible to visualize the net-positive charge for both atoms. In addition, in both experimental data and simulations, it is possible to detect the net-negative charge surrounding the Ga atomic nucleus: the electron cloud. The authors suggest that this work is a critical step toward the direct atomic-scale determination of the local charge redistributions and modulations taking place in materials systems. The next challenge for DPC-STEM, they add, will be to map charge redistributions between atoms, thus visualizing bonding valence electrons in real space.
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