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COMFORTABLY NUMB IN A NANOENCAPSULATED WAY For over a century, doctors have anesthetized extremities for surgeries using intravenous regional anesthesia, a procedure commonly known as a Bier block. This technique involves isolating the selected extremity from the rest of circulation with a tourniquet and injecting local anesthetics. Although Bier blocks are reliable, cost-effective, and easy to administer by skilled personnel, they have several limitations, including pain from the required tourniquet, toxicity that can occur from systemic release of the injected anesthetics, and a lack of postoperative pain relief that necessitates systemic medications such as opioids or regional anesthetic techniques. To overcome these drawbacks, Weldon et al. (DOI: 10.1021/ acsnano.8b05408) developed a delivery formulation in which the local anesthetic is nanoencapsulated. Working with bupivacaine, a potent and long-acting anesthetic whose use is limited by risks of cardiac toxicity, the researchers developed two different formulations of nanoparticles: micelles with 15 nm diameters and liposomes with 100 nm diameters, differently sized to test the effect of this variable on outcomes. They then assessed these particles in vitro and in a model of Bier block using the rat tail vein. They found that both particle sizes exhibited controlled release compared with free bupivacaine and markedly reduced cytotoxicity. However, the micellar formulation had significantly higher local retention than the liposomal formulation after tourniquet release, and it provided tail analgesia for more than twice as long with one-fifth the dose of free bupivacaine. The authors suggest that the enhancement of efficacy and safety in the micellar formulation suggest that it may offer a significant advance for regional anesthesia.
as biphasic reaction media. For example, regeneration of reagent and product retrieval from the droplet reactors are challenging; similarly, the discrete nature of each droplet impedes the development of a continuous biphasic process. Thus, simultaneous reaction and separation cannot be performed in these systems. Recently, the development of bicontinuous interfacially jammed emulsion gels (bijels) composed of continuous domains of oil in contact with continuous domains of water stabilized by the jamming of interfacially trapped nanoparticles, has shown promise toward this goal. However, bijels tend to be fragile and to lose their integrity under the changes of solution conditions and mechanical agitation required to drive many reactions. To fortify these materials, Di Vitantonio et al. (DOI: 10.1021/ acsnano.8b05718) modified the solvent transfer-induced phase separation (STRIPS) synthesis method to trap a layer of silica nanoparticles interfacially. Although the bicontinuous morphology of the bijel is preserved, this step adds robustness that protects the structure from changes in solution pH and application of mechanical stresses, such as stirring. The researchers demonstrate that these materials could be used for reactive separation by demonstrating the base-catalyzed hydrolysis of ethyl acetate, with complete conversion and recovery of products. The authors suggest that by using catalytically active oxides such as alumina and titania as the reinforcing materials, it will be possible to perform biphasic reactive separations under even more challenging conditions.
ALL-TWO-DIMENSIONAL CAPACITORS THAT ARE FIT TO PRINT Two-dimensional (2D) materials, such as graphene and hexagonal boron nitride (hBN) have been extensively explored as components for next-generation nanoelectronic devices due to their numerous benefits, such as straightforward integration with existing fabrication processes and the ability to transfer
SIMULTANEOUS REACTION AND SEPARATION WITH ROBUST BIJELS Pickering emulsions, oil and water emulsions stabilized by solid particles, have been extensively used as media for catalysis and separation. However, they have drawbacks that hinder their use © 2019 American Chemical Society
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Published: January 22, 2019 4
DOI: 10.1021/acsnano.9b00225 ACS Nano 2019, 13, 4−7
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onto any substrate, including flexible ones. Two-dimensional materials can also be stacked into different heterostructures with intriguing electronic properties. With the large family of 2D crystals already isolated and being investigated, integrated circuits could conceivably be composed completely of 2D materials. Toward that end, Worsley et al. (DOI: 10.1021/ acsnano.8b06464) demonstrate all-2D capacitors made through inkjet printing. This method is relatively inexpensive and quick, has no material wastage, and is compatible with almost any surface of interest. The researchers used water-based and biocompatible graphene and hBN inks to compose these capacitors, first printing a layer of graphene as the bottom electrode, then hBN as the dielectric, then graphene again as the top electrode. Tests showed an areal capacitance of 2.0 ± 0.3 nF cm−2 for a dielectric thickness of ∼3 μm and negligible leak currents, averaged across more than 100 devices. This printed hBN has a dielectric constant of 6.1 ± 1.7 and a breakdown strength of 1.9 ± 0.3 MV cm−1. Further experiments showed that these devices could be incorporated into a resistor-capacitor low-pass filter and a graphene-based field effect transistor. The authors suggest that more complex circuits can be developed by printing other types of components, such as diodes and highmobility transistors.
these markers were about 2.1 nm apart; after light exposure, this distance shrank to about 1.4 nm, indicative of a trans-to-cis photoisomerization. Additional experiments showed that light illumination of these molecules on their graphene supports caused their diffusion out from initial clusters to the surrounding areas of graphene, suggesting that these changes in conformation overcome the intermolecular van der Waals interactions. The authors suggest that metal markers could provide an effective way to study a diverse range of complex organic materials at the single molecule level.
GOLD NANOPARTICLES FEEL THE PULL OF OPTICAL STRETCHING Lasers have long been used in nanoscience, where they can generate multiphysical effects. For example, a tightly focused beam can produce both thermal and optical forces around the confocal point, which can be exploited for optically controlled nanolithography and nanofabrication. One laser-related application that has recently been explored is tuning plasmonic resonances with light, where lasers are applied either to fabricate and to deform gold nanoparticles in solution via ablation or to move the gold atoms of nanoparticles to tune their plasmon resonances continuously. However, studies thus far have all been based on photothermal effects that cause irreversible changes in the gold nanoparticles, leading them to become thermodynamically stable spheres or merged spheres. It is more challenging to transform them into nanorods or dimers that can be used to match the required resonances of nanophotonic devices. Wang and Ding (DOI: 10.1021/acsnano.8b06087) accomplished this goal by using a 446 nm continuous wave laser to irradiate gold nanoparticles on a Si substrate. Experiments show that as the irradiation proceeds, the plasmon resonance of the particles progressively red-shifts, attributed to the light-induced formation of gold nanorods from the original spheres. Simulations suggest an optical stretching mechanism, in which thermal and optical forces work synergistically to pull the particles after they are partially melted. By applying even higher laser power, the researchers were able to shrink the elongated particles back to spheres, showing that this process is reversible. In addition, by manipulating the surface tension of the substrate, the researchers pulled some nanoparticles into dimers. They suggest that this method provides a facile way of tailoring plasmonic properties with light.
WATCHING PHOTOSWITCHING WITH METAL MARKERS Photoswitching molecules, which reversibly change conformation with exposure to light, have the potential for a variety of applications such as liquid crystal assembly, sensing, surface functionalization for controlling hydrophobicity, and drug delivery. These molecules have been widely investigated both for these applications and to develop better fundamental understanding of their photophysics, typically through optical methods and nuclear magnetic resonance studies. Some rare photoswitching molecules, such as perfluorinated azobenzene, can be crystallized after light activation to enable elucidation of the resulting isomer. However, the slow nature of crystallography sample preparation often fails to capture these metastable isomers. Looking for a different way to visualize photoswitching molecular conformations, Gerkman et al. (DOI: 10.1021/ acsnano.8b08441) report a method that enabled them to image evidence of cis and trans configurations directly by measuring the distance between metal atom markers. The researchers designed photoswitching azobenzene derivatives with ligands at each end containing single Pt atoms. Using annular dark-field scanning transmission electron microscopy (ADF-STEM), they measured the distance between these markers both before and after light irradiation. Their results show that before light exposure, 5
DOI: 10.1021/acsnano.9b00225 ACS Nano 2019, 13, 4−7
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WRITING BRIGHT WITH NEAR-PERCOLATION PLASMONIC REFLECTOR ARRAYS Structural coloration has gained increasing attention as a commercial technology with significant advantages over dyes, such as making use of environmentally friendly, recyclable materials and generating nonbleaching color. Recent reports show that it is possible to accomplish coloration by surface nanostructuring through the use of laser postprocessing of specially designed and fabricated nanostructures. Taking this idea a step further, Roberts et al. (DOI: 10.1021/ acsnano.8b07541) did away with preformed nanostructures and used lasers to write bright colors directly on near-percolation metal films on top of dielectric-metal sandwiches. The researchers used near-percolation plasmonic reflector arrays (NPPRAs) composed of 4 nm-thick gold films evaporated on 30 nm thick silica layers atop optically thick (100 nm) gold films supported by silicon substrates. Their experiments show that the heat from a strongly focused Ti-sapphire laser beam gradually merges and reshapes the differently sized nanoparticles in the gold film, changing the color of reflected light. Varying the power of the laser, they produced bright and deeply saturated colors ranging from yellow for the pristine sample and lowpower exposures to green for intermediate powers to red for the largest powers with subwavelength resolution. These color prints could be protected with a transparent dielectric overlay for ambient use without destroying the coloring. In addition, the researchers show that it is possible to perform their laser color printing technique on polymer-protected NPPRAs. The authors suggest that each of these features makes this technique amenable for applications ranging from nanoscale patterning for security marking to large-scale color printing for decoration.
MAKING CANCER TREATMENTS MORE EFFECTIVE, LESS TOXIC Irinotecan is a chemotherapeutic agent frequently prescribed for gastrointestinal (GI) cancers, including colorectal cancer (CRC) and pancreatic ductal adenocarcinoma (PDAC). Although this drug can significantly extend survival, its use is hindered by high toxicity, particularly to the bone marrow and GI tract. To help curb its toxic effects, researchers have developed several alternative delivery strategies, including encapsulated it in nanocarriers such as liposomes. One liposomal carrier in particular, known as Onivyde, was approved in 2015 as part of a combination strategy for metastatic PDAC. However, this formulation also exerts toxic effects, with “black box” safety warnings citing the possibility of life-threatening neutropenia and severe diarrhea. Seeking a better way to deliver irinotecan, Liu et al. (DOI: 10.1021/acsnano.8b06164) developed “silicasome” nanocarriers made of mesoporous silica nanoparticles wrapped with a lipid bilayer. In vitro tests showed that irinotecan packaged in this carrier could kill CRC and PDAC cells more effectively than in the liposomal carrier. In a murine orthotopic tumor chunk model of colon cancer, the circulatory half-life of the silicasomes was nearly three times as long as the liposomal carrier and resulted in significantly higher drug content at the tumor site. More importantly, irinotecan in the liposomal carrier inhibited tumor growth more effectively than the free drug and liposomal carrier, leading to a significant survival benefit, all with major reductions in bone marrow and GI tract toxicity. In addition, the irinotecan silicasomes also showed promise in a murine PDAC model. The authors suggest that this carrier could offer a better treatment strategy for delivering irinotecan and potentially other chemotherapeutic agents.
BRINGING BETTER NANOPORE-BASED SENSING TO LIGHT Nanopores have attracted significant attention as biosensors that have promise in numerous areas of personalized medicine. Thus far, nanopore-based methods have relied almost exclusively on changes in ionic current as feedback while analytes pass through the nanopores. However, the ionic current is set up by a transmembrane driving voltage that controls the translocation speed of the molecules, inextricably linking the signal strength and translocation time. This method also requires a strong electrolyte solution, making sensing at physiological conditions impossible, and the need for individual current amplifiers for read-out of each nanopore, which limits sensor density on chips. Looking for a solution to these problems, Verschueren et al. (DOI: 10.1021/acsnano.8b06758) developed a nanopore 6
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commercial application that relies on the properties of 2D monolayers of these materials.
detection method that uses enhanced light transmission rather than ionic current. Their scheme relies on a plasmonic antenna shaped like a bowtie, drilled into a 100 nm thick gold film. This nanoaperture has a nanopore drilled into its gap. Illuminating it with a laser polarized across the feed gap direction of the antenna excites a plasmon resonance that enhances and concentrates the electromagnetic field to the hotspot in the gap of the antenna. Experiments show that these plasmonic nanopores act as optical single-molecule sensors, detecting DNA translocations by changes in the transmitted light intensity. This method required no labels and performed effectively at physiological salt concentrations, conditions where traditional ionic current sensing fails. The authors suggest that the signal could eventually be improved by bringing the resonance of the plasmonic nanoantennas closer to the excitation laser or by modifying the antenna layout.
GIVING TWO-DIMENSIONAL MATERIALS THAT EXTRA POLISH In recent years, a host of two-dimensional (2D) materials have been discovered. These materials have shown extraordinary properties that could be useful in a wide range of applications, such as high temperature conductivity, superlubricity, charge density wave, piezotronics, flextronics, straintronics, spintronics, valleytronics, and optoelectronics. However, these properties manifest mostly in monolayers. Although researchers have made significant progress in recent years toward synthesizing large area sections of some 2D materials through physical vapor deposition and chemical vapor deposition techniques, avoiding the nucleation and subsequent growth of multilayers remains a challenge for maintaining consistent electronic and optoelectronic properties. Toward creating reliable monolayers, Sebastian et al. (DOI: 10.1021/acsnano.8b08216) report a method that uses an electrochemical polishing technique that removes additional layers without harming the integrity or exceptional properties of monolayers. Demonstrating this method on MoS2 and WS2, the researchers transferred flakes of these materials onto conductive TiN substrates, then placed them in a three-terminal electrochemical cell. After applying a relatively small anodic potential, the multilayer regions of the flakes corrode, converting to monolayers over the entire substrate. Tests show that this method works on flakes of any initial size, shape, and thickness, and it is inherent to 2D transition-metal dichalcogenides due to the stability of their basal planes, enhanced edge reactivity, and stronger than van der Waals interactions with the substrate. The authors suggest that this method could be used for any 7
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