Intrinsic Magnetic Order of Chemically Exfoliated 2D Ruddlesden-Popper Organic-Inorganic Halide Perovskite Ultrathin Films.

Thin film fabrication of 2D layered organic-inorganic hybrid perovskites (2D-OIHPs) for spintronic applications has been attempted using solution-based process like Langmuir-Blodgett technique. However, monolayer or few-layered 2D magnets are not yet realized, even though a wide spectrum of 2D Ruddlesden-Popper (RP) OIHPs are known as quasi-2D Heisenberg magnets in bulk compounds. Here, chemical exfoliation by solvent engineering is applied to successfully synthesize large-sized, few unit-cell-thick 2D RP-OIHPs. Comprehensive structural characterization reveals that binary co-solvents with high relative polarity in spin coating technique are the most effective among nine kinds of solvents. Above all, this enables few-layered 2D RP-OIHP ultrathin films sustaining their intrinsic magnetic order. It is found that XY-like magnetic anisotropy driven by Jahn-Teller effect responsible for ferromagnetism in seven-layered (C6 H5 CH2 CH2 NH3 )2 CuCl4 ultrathin films remains very robust, whereas Ising-like dipolar anisotropy responsible for canted antiferromagnetism in ten-layered (C6 H5 CH2 CH2 NH3 )2 MnCl4 ultrathin films is greatly reduced. It is expected that ferromagnetism even at monolayer limit should be possible by means of further sophisticated solvent engineering as long as Jahn-Teller effect is active. The chemical exfoliation using solvent engineering unambiguously can bring about a new breakthrough in the development of 2D RP-OIHP van der Waals magnets for ultrahigh energy-efficient spintronic, opto-spintronic devices.

Poly(ethylene glycol)- and carboxylate-functionalized gold nanoparticles using polymer linkages: single-step synthesis, high stability, and plasmonic detection of proteins.

Gold nanoparticles with suitable surface functionalities have been widely used as a versatile nanobioplatform. However, functionalized gold nanoparticles using thiol-terminated ligands have a tendency to aggregate, particularly in many enzymatic reaction buffers containing biological thiols, because of ligand exchange reactions. In the present study, we developed a one-step synthesis of poly(ethylene glycol) (PEG)ylated gold nanoparticles using poly(dimethylaminoethyl methacrylate) (PDMAEMA) in PEG as a polyol solvent. Because of the chelate effect of polymeric functionalities on the gold surface, the resulting PEGylated gold nanoparticles (Au@P-PEG) are very stable under the extreme conditions at which the thiol-monolayer-protected gold nanoparticles are easily coagulated. Using the solvent mixture of PEG and ethylene glycol (EG) and subsequent hydrolysis, gold nanoparticles bearing mixed functionalities of PEG and carboxylate are generated. The resulting particles exhibit selective adsorption of positively charged chymotrypsin (ChT) without nonselective adsorption of bovine serum albumin (BSA). The present nanoparticle system has many advantages, including high stability, simple one-step synthesis, biocompatibility, and excellent binding specificity; thus, this system can be used as a versatile platform for potential bio-related applications, such as separation, sensing, imaging, and assays.

Activation of NFAT by HGF and IGF-1 via ARF6 and its effector ASAP1 promotes uveal melanoma metastasis.

Preventing or effectively treating metastatic uveal melanoma (UM) is critical because it occurs in about half of patients and confers a very poor prognosis. There is emerging evidence that hepatocyte growth factor (HGF) and insulin-like growth factor 1 (IGF-1) promote metastasis and contribute to the striking metastatic hepatotropism observed in UM metastasis. However, the molecular mechanisms by which HGF and IGF-1 promote UM liver metastasis have not been elucidated. ASAP1, which acts as an effector for the small GTPase ARF6, is highly expressed in the subset of uveal melanomas most likely to metastasize. Here, we found that HGF and IGF-1 hyperactivate ARF6, leading to its interaction with ASAP1, which then acts as an effector to induce nuclear localization and transcriptional activity of NFAT1. Inhibition of any component of this pathway impairs cellular invasiveness. Additionally, knocking down ASAP1 or inhibiting NFAT signaling reduces metastasis in a xenograft mouse model of UM. The discovery of this signaling pathway represents not only an advancement in our understanding of the biology of uveal melanoma metastasis but also identifies a novel pathway that could be targeted to treat or prevent metastatic uveal melanoma.

Plasmonic monitoring of catalytic hydrogen generation by a single nanoparticle probe.

Plasmonic nanostructures such as gold nanoparticles are very useful for monitoring chemical reactions because their optical properties are highly dependent upon the environment surrounding the particle surface. Here, we designed the catalytic structure composed of platinized cadmium sulfide with gold domains as a sensitive probe, and we monitored the photocatalytic decomposition of lactic acid to generate hydrogen gas in situ by single-particle dark-field spectroscopy. The plasmon band shift of the gold probe throughout the reaction exhibits significant particle-to-particle variation, and by simulating the reaction kinetics, the rate constant and structural information (including the diffusion coefficient through the shell and the relative arrangement of the active sites) can be estimated for individual catalyst particles. This approach is versatile for the monitoring of various heterogeneous reactions with distinct components at a single-particle level.

Full-color tuning of surface plasmon resonance by compositional variation of Au@Ag core-shell nanocubes with sulfides.

In the present study, we demonstrate the precise tuning of surface plasmon resonance over the full visible range by compositional variation of the nanoparticles. The addition of sulfide ions into the Au@Ag core-shell nanocubes generates stable Au@Ag/Ag(2)S core-shell nanoparticles at room temperature, and the plasmon extinction maximum shifts to the longer wavelength covering the entire visible range of 500-750 nm. Based on the optical property, the Au@Ag core-shell nanocubes are employed as a colorimetric sensing framework for sulfide detection in water. The detection limit is measured to be 10 ppb by UV-vis spectroscopy and 200 ppb by naked eyes. Such nanoparticles would be useful for decoration and sensing purposes, due to their precise color tunability and high stability.

Type I Interferon Signaling Is Critical During the Innate Immune Response to HSV-1 Retinal Infection.

Purpose: Acute retinal necrosis (ARN) is a herpesvirus infection of the retina with blinding complications. In this study, we sought to create a reproducible mouse model of ARN that mimics human disease to better understand innate immunity within the retina during virus infection. Methods: C57Bl/6J wild type (WT) and type I interferon receptor-deficient (IFNAR-/-) mice were infected with varying amounts of herpes simplex virus type 1 (HSV-1) via subretinal injection. Viral titers, optical coherence tomography (OCT) and fundus photography, the development of encephalitis, and ocular histopathology were scored and compared between groups of WT and IFNAR-/- mice. Results: The retina of WT mice could be readily infected with HSV-1 via subretinal injection resulting in retinal whitening and full-thickness necrosis as determined by in vivo imaging and histopathology. In IFNAR-/- mice, HSV-1-induced retinal pathology was significantly worse when compared with WT mice, and viral titers were significantly elevated within two days after infection and persisted to day 5 after infection within the retina. These results were also observed in the brain where there were significantly higher viral titers and frequency of encephalitis in IFNAR-/- when compared to WT mice. Conclusions: Collectively, these findings show that our new mouse model of ARN mimics human disease and can be used to study innate immunity within the retina. We conclude that type I interferons are critical in containing HSV-1 locally within retinal tissues and prohibiting spread into the brain.

Coordination power adjustment of surface-regulating polymers for shaping gold polyhedral nanocrystals.

PVP (poly(vinyl pyrrolidone)) is a common polymer that behaves as a surface-regulating agent that shapes metal nanocrystals in the polyol process. We have used different polymers containing tertiary amide groups, namely PVCL (poly(vinyl caprolactam)) and PDMAm (poly(N,N-dimethyl acrylamide)), for the synthesis of gold polyhedrons, including octahedrons, cuboctahedrons, cubes, and higher polygons, under the present polyol reaction conditions. The basicity and surface coordination power of the polymers are in the order of PVCL, PVP, and PDMAm. A correlation is observed between the coordination power of the polymers and the resulting gold nanocrystal size. Strong coordination and electron donation from the polymer functional groups to the gold surface restrict particle growth rates, which leads to small nanocrystals. The use of PVCL can yield gold polyhedral structures with small sizes, which cannot be achieved in the reactions with PVP. Simultaneous hydrolysis of the amide group in PDMAm leads to carboxylate functionality, which is very useful for generating chemical and bioconjugates through the formation of ester and amide bonds.

Copper(I) coordination polymers of N,N'-bis[3-(methylthio)propyl]pyromellitic diimide: crystal transformation and solvatochromism by halogen-π interactions.

Four copper(I) coordination polymers with ligand N,N'-bis[3-(methylthio)propyl]pyromellitic diimide (L), [Cu(2)I(2)L(2)](n) (1), [Cu(2)I(2)L(2)](n) (2), [Cu(2)I(2)L](n) (3), and {[Cu(2)I(2)L(2)]·CH(2)Cl(2)}(n) (4), have been successfully synthesized and structurally characterized by single-crystal X-ray diffraction. Structural transformations between the polymers were controlled by the appropriate solvent composition, mole ratio, or temperature. When a 1:1 CuI/L ratio was employed, dimorphic products, 1 and 2, based on a rhomboid Cu(2)I(2) cluster were obtained from an acetonitrile solution and from a dichloromethane/acetonitrile solution with ultrasonication, respectively. When a 1:2 CuI/L ratio was employed, polymer 3 based on infinite stair-step polymer (CuI)(∞) was crystallized. Crystalline product 4 was obtained by the transformation of 1 in a mixed-solvent system with a 1:5 acetonitrile/dichloromethane ratio. Polymers 1-4 were transformed into polymer 3 at 197 °C. X-ray structures of 2-4 show short distances (3.406-3.667 Å) between halogens (I(-) and Cl) and aromatic rings. 1 and 4 show solvatochromism; upon inclusion of the colorless electron donor CH(2)Cl(2), the red color changes as a result of the formation of a chloride-π charge-transfer complex 4 of a pale-colored electron acceptor, 1. Therefore, the origin of the red color from 2 and 3 is also assigned as iodide-to-electron-deficient aromatic π charge transfer.

Solvent-dependent self-assembly of two dimensional layered perovskite (C6H5CH2CH2NH3)2MCl4 (M = Cu, Mn) thin films in ambient humidity.

Two dimensional layered organic-inorganic halide perovskites offer a wide variety of novel functionality such as solar cell and optoelectronics and magnetism. Self-assembly of these materials using solution process (ex. spin coating) makes crystalline thin films synthesized at ambient environment. However, flexibility of organic layer also poses a structure stability issue in perovskite thin films against environment factors (ex. moisture). In this study, we investigate the effect of solvents and moisture on structure and property in the (C6H5(CH2)2NH3)2(Cu, Mn)Cl4 (Cu-PEA, Mn-PEA) perovskite thin films spin-coated on Si wafer using three solvents (H2O, MeOH, MeOH + H2O). A combination of x-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) show that relative humidity (RH) has a profound effect on perovskite thin films during sample synthesis and storage, depending on the kind of solvent used. The ones prepared using water (Cu-PEA:H2O, Mn-PEA:H2O) show quite different behavior from the other cases. According to time-dependent XRD, reversible crystalline-amorphous transition takes place depending on RH in the former cases, whereas the latter cases relatively remain stable. It also turns out from XAS that Mn-PEA thin films prepared with solvents such as MeOH and MeOH + H2O are disordered to the depth of about 4 nm from surface.

Au@Ag core-shell nanocubes for efficient plasmonic light scattering effect in low bandgap organic solar cells.

In this report, we propose a metal-metal core-shell nanocube (NC) as an advanced plasmonic material for highly efficient organic solar cells (OSCs). We covered an Au core with a thin Ag shell as a scattering enhancer to build Au@Ag NCs, which showed stronger scattering efficiency than Au nanoparticles (AuNPs) throughout the visible range. Highly efficient plasmonic organic solar cells were fabricated by embedding Au@Ag NCs into an anodic buffer layer, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and the power conversion efficiency was enhanced to 6.3% from 5.3% in poly[N-9-hepta-decanyl-2,7-carbazole-alt-5,5-(4,7-di-2-thienyl-2,1,3-benzothiadiazole)] (PCDTBT):[6,6]-phenyl C71-butyric acid methyl ester (PC70BM) based OSCs and 9.2% from 7.9% in polythieno[3,4-b]thiophene/benzodithiophene (PTB7):PC70BM based OSCs. The Au@Ag NC plasmonic PCDTBT:PC70BM-based organic solar cells showed 2.2-fold higher external quantum efficiency enhancement compared to AuNPs devices at a wavelength of 450-700 nm due to the amplified plasmonic scattering effect. Finally, we proved the strongly enhanced plasmonic scattering efficiency of Au@Ag NCs embedded in organic solar cells via theoretical calculations and detailed optical measurements.