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Upconverting nanoparticles provide valuable benefits as optical probes for bioimaging and Förster resonant energy transfer (FRET) due to their high signal-to-noise ratio, photostability, and biocompatibility; yet, making nanoparticles small yields a significant decay in brightness due to increased surface quenching. Approaches to improve the brightness of UCNPs exist but often require increased nanoparticle size. Here we present a unique core-shell-shell nanoparticle architecture for small (sub-20 nm), bright upconversion with several key features: (1) maximal sensitizer concentration in the core for high near-infrared absorption, (2) efficient energy transfer between core and interior shell for strong emission, and (3) emitter localization near the nanoparticle surface for efficient FRET. This architecture consists of β-NaYbF 4 (core) @NaY 0.8-x Er x Gd 0.2 F 4 (interior shell) @NaY 0.8 Gd 0.2 F 4 (exterior shell), where sensitizer and emitter ions are partitioned into core and interior shell, respectively. Emitter concentration is varied (x = 1, 2, 5, 10, 20, 50, and 80%) to investigate influence on single particle brightness, upconversion quantum yield, decay lifetimes, and FRET coupling. We compare these seven samples with the field-standard core-shell architecture of β-NaY 0.58 Gd 0.2 Yb 0.2 Er 0.02 F 4 (core) @NaY 0.8 Gd 0.2 F 4 (shell), with sensitizer and emitter ions codoped in the core. At a single particle level, the core-shell-shell design was up to 2-fold brighter than the standard core-shell design. Further, by coupling a fluorescent dye to the surface of the two different architectures, we demonstrated up to 8-fold improved emission enhancement with the core-shell-shell compared to the core-shell design. Finally, we show how, given proper consideration for emitter concentration, we can design a unique nanoparticle architecture to yield comparable or improved brightness and FRET coupling within a small volume.
Lattice mismatch in core/shell nanoparticles occurs when the core and shell materials have different lattice parameters. When there is a significant lattice mismatch, a coherent core-shell interface results in substantial lattice strain energy, which can affect the shell morphology. The shell can be of uniform thickness or can be rough, having thin and thick regions. A smooth shell minimizes the surface energy at the expense of increased lattice strain energy and a rough shell does the opposite. A quantitative treatment of the lattice strain energy in determining the shell morphology of CdSe/CdS core/shell nanoparticles is presented here. We use the inhomogeneity in hole tunneling rates through the shell to adsorbed hole acceptors to quantify the extent of shell thickness inhomogeneity. The results can be understood in terms of a model based on elastic continuum calculations, which indicate that the lattice strain energy depends on both core size and shell thickness. The model assumes thermodynamic equilibrium, i.e., that the shell morphology corresponds to a minimum total (lattice strain plus surface) energy. Comparison with the experimental results indicates that CdSe/CdS nanoparticles undergo an abrupt transition from smooth to rough shells when the total lattice strain energy exceeds about 27 eV or the strain energy density exceeds 0.59 eV/nm{sup 2}. We also find that the predictions of this model are not followed for CdSe/CdS nanoparticles when the shell is deposited at very low temperature and therefore equilibrium is not established.
Developing structure-performance relationships with the underlying goal of optimizing known zeolite catalysts involves the manipulation of their physicochemical properties. Here, we systematically assessed the impact of mesoscopic gradients in acid site concentration, which has generally received little attention in the design of zeolite catalysts for hydrocarbon upgrading. A series of core–shell MEL-type zeolites were synthesized with catalytically active ZSM-11 cores and passivated silicalite-2 shells of varying thickness. Our findings revealed that ZSM-11@silicalite-2 particles with ultrathin shells (<10 nm) have enhanced mass transport, characteristic of relatively smaller particles, compared to the corresponding ZSM-11 core. Additionally, catalytic testing using the methanol-to-hydrocarbon (MTH) reaction showed that core–shell zeolites exhibit longer lifetimes, higher total turnovers, and an unexpected promotion of the aromatic cycle in the hydrocarbon pool mechanism. Time-resolved acid titration of core and core–shell catalysts confirmed that the siliceous shell introduces a hydrophobic exterior that impacts molecular diffusion. In comparison, prepared MFI core-shells (ZSM-5@silicalite-1) showed similar enhancement in catalyst performance. Moreover, we prepared egg-shell configurations of each zeolite, silicalite-2@ZSM-11 and silicalite-1@ZSM-5, comprised of an inert core and catalytically active shell. This inverse design of the egg-shell created pseudo nanosheets with total turnovers that were markedly higher than their homogeneous counterparts. Collectively, this study demonstrated that mesoscopic gradients in acid concentration via the design of core–shell and egg-shell zeolites significantly improve catalyst performance over conventional analogues for hydrocarbon upgrading.
Surrogate implosions play an important role at the National Ignition Facility (NIF) for isolating aspects of the complex physical processes associated with fully integrated ignition experiments. The newly developed CD Symcap platform has been designed to study gas-shell mix in indirectly driven, pure T{sub 2}-gas filled CH-shell implosions equipped with 4 μm thick CD layers. This configuration provides a direct nuclear signature of mix as the DT yield (above a characterized D contamination background) is produced by D from the CD layer in the shell, mixing into the T-gas core. The CD layer can be placed at different locations within the CH shell to probe the depth and extent of mix. CD layers placed flush with the gas-shell interface and recessed up to 8 μm have shown that most of the mix occurs at the inner-shell surface. In addition, time-gated x-ray images of the hotspot show large brightly radiating objects traversing through the hotspot around bang-time, which are likely chunks of CH/CD plastic. This platform is a powerful new capability at the NIF for understanding mix, one of the key performance issues for ignition experiments.
We have examined the effects of core-shell intermixing on the dynamical magnetism of γ-Fe{sub 2}O{sub 3}/MnO nanoparticles. The core and shell phases were identified using x-ray diffraction, and x-ray absorption spectroscopy identified Mn ions in both octahedral and tetrahedral sites, consistent with a significant amount of substitution at the core-shell interface to form an Fe/Mn-ferrite. The dynamical response was probed by Mössbauer spectroscopy, which decouples surface and core spins, and suggested a change in the relaxation behaviour among the spin populations within γ-Fe{sub 2}O{sub 3}/MnO relative to the γ-Fe{sub 2}O{sub 3} seed particles. Interestingly, the magnetic relaxation effects at the atomic scale, measured via Mössbauer spectroscopy, were enhanced, indicating that the addition of an MnO shell and intermixing affected the dynamical freezing process which altered the surface magnetism of the γ-Fe{sub 2}O{sub 3} core. Our results show that both the MnO shell and the interfacial intermixed layer are important in determining the core-shell nanoparticle magnetism.
The structure, electrochemistry, and thermal stability of concentration gradient core–shell (CGCS) particles with different shell morphologies were evaluated and compared. We modified the shell morphology from nanoparticles to nanorods, because nanorods can result in a reduced surface area of the shell such that the outer shell would have less contact with the corrosive electrolyte, resulting in improved electrochemical properties. Electron microscopy studies coupled with electron probe X-ray micro-analysis revealed the presence of a concentration gradient shell consisting of nanoparticles and nanorods before and after thermal lithiation at high temperature. Rietveld refinement of the X-ray diffraction data and the chemical analysis results showed no variations of the lattice parameters and chemical compositions of both produced CGCS particles except for the degree of cation mixing (or exchange) in Li and transition metal layers. As anticipated, the dense nanorods present in the shell gave rise to a high tap density (2.5 g cm3 ) with a reduced pore volume and surface area. Intimate contact among the nanorods is likely to improve the resulting electric conductivity. As a result, the CGCS Li[Ni0.60Co0.15Mn0.25]O2 with the nanorod shell retained approximately 85.5% of its initial capacity over 150 cycles in the range of 2.7–4.5 V at 608C. The charged electrode consisting of Li0.16[Ni0.60Co0.15Mn0.25]O2 CGCS particles with the nanorod shell also displayed a main exothermic reaction at 279.48C releasing 751.7 J g1 of heat. Due to the presence of the nanorod shell in the CGCS particles, the electrochemical and thermal properties are substantially superior to those of the CGCS particles with the nanoparticle shell.
We present a semi-quantitative model of condensation of short nucleic acid (NA) duplexes induced by trivalent cobalt(III) hexammine (CoHex) ions. The model is based on partitioning of bound counterion distribution around single NA duplex into “external” and “internal” ion binding shells distinguished by the proximity to duplex helical axis. In the aggregated phase the shells overlap, which leads to significantly increased attraction of CoHex ions in these overlaps with the neighboring duplexes. The duplex aggregation free energy is decomposed into attractive and repulsive components in such a way that they can be represented by simple analytical expressions with parameters derived from molecular dynamic simulations and numerical solutions of Poisson equation. The attractive term depends on the fractions of bound ions in the overlapping shells and affinity of CoHex to the “external” shell of nearly neutralized duplex. The repulsive components of the free energy are duplex configurational entropy loss upon the aggregation and the electrostatic repulsion of the duplexes that remains after neutralization by bound CoHex ions. The estimates of the aggregation free energy are consistent with the experimental range of NA duplex condensation propensities, including the unusually poor condensation of RNA structures and subtle sequence effects upon DNA condensation. The model predicts that, in contrast to DNA, RNA duplexes may condense into tighter packed aggregates with a higher degree of duplex neutralization. An appreciable CoHex mediated RNA-RNA attraction requires closer inter-duplex separation to engage CoHex ions (bound mostly in the “internal” shell of RNA) into short-range attractive interactions. The model also predicts that longer NA fragments will condense more readily than shorter ones. The ability of this model to explain experimentally observed trends in NA condensation lends support to proposed NA condensation picture based on the multivalent “ion binding shells.”.
We report that argon gas puffs have produced 330 kJ ± 9% of x-ray radiation above 3 keV photon energy in fast z-pinch implosions, with remarkably reproducible K-shell spectra and power pulses. This reproducibility in x-ray production is particularly significant in light of the variations in instability evolution observed between experiments. Lastly, soft x-ray power measurements and K-shell line ratios from a time-resolved spectrum at peak x-ray power suggest that plasma gradients in these high-mass pinches may limit the K-shell radiating mass, K-shell power, and K-shell yield from high-current gas puffs.
Catalytically active individual gold (Au) and cerium oxide (CeO2) nanoparticles are well known to exhibit specific enzyme-like activities, such as natural catalase, oxidase, superoxide dismutase, and peroxidase enzymes. These activities have been maneuvered to design several biological applications such as immunoassays, glucose detection, radiation and free radical protection and tissue engineering. A functional nanozyme depicting multienzyme like properties that functions as a synthetic super enzyme has eluded the researchers in the nanoscience community for past decade. In current report, we have designed a functional multienzyme in the form of Gold (core)-CeO2 (shell) nanoparticles (Au@CeO2 CSNPs) exhibiting excellent peroxidase, catalase and superoxide dismutase enzyme-like activities that are controlled simply by tuning the pH. The reaction kinetic parameters reveal that the peroxidase-like activity of this core shell nanozyme is comparable to natural HRP enzyme. Unlike peroxidase-like activity exhibited by other nanomaterials, Au@CeO2 CSNPs showed decrease in hydroxyl radical formation, suggesting that the bio catalytic reactions are performed by efficient electron transfers. A significant enzyme-like activity of this core shell nanoparticle was conserved at extreme pH (2 – 11) and temperatures (up to 90 °C), clearly suggesting the superiority over natural enzymes. Further, the utility of peroxidase-like activity of this core shell nanoparticles was extended for the detection of glucose, which showed a linear range of detection between (100 µM – 1 mM). It is hypothesized that the proximity of the redox potentials of Au+/Au and Ce (III)/Ce (IV) may result in a redox couple promoting the multienzyme activity of core shell nanoparticles. Au@CeO2 CSNPs may open new directions for development of single platform sensors in multiple biosensing applications.
Polar-driven direct-drive experiments recently performed on the OMEGA Laser System have demonstrated the efficacy of using a target with a contoured shell with varying thickness to improve the symmetry and fusion performance of the implosion. The polar-driven contoured-shell implosions have substantially reduced low mode perturbations compared to polar-driven spherical-shell implosions as diagnosed by x-ray radiographs up to shell stagnation. As a result, fusion yields were increased by more than a factor of ~2 without increasing the energy of the laser by the use of contoured shells.
Using high-resolution (FWHM approximately 0.05 A) ultraviolet spectral data obtained with Copernicus, the nature of shell lines in Be and shell stars. Scans were obtained for various excited fine-structure lines of Fe III, Si II, and O I. It is found that Be stars, in general, do not display shell lines in the ultraviolet, contrary to the findings of previous work at lower resolution. The only Be stars that display strong UV shell lines are the 'classical' shell stars, i.e., stars that also display shell lines in the optical region. Furthermore, it is found that the shell lines, when present, have essentially zero velocity shift with respect to the star. The resonance shell lines seen in the shell stars are generally asymmetric on the short-wavelength side, indicating that the lines are formed in a low-velocity outflowing region. The results presented here argue strongly in favor of a flattened disk structure for the shell line forming region, and against some recent scenarios involving spherical symmetry.
In warm target direct-drive ICF implosion experiments performed at the OMEGA laser facility, plastic microballoons doped with a titanium tracer layer in the shell and filled with deuterium gas were imploded using a low-adiabat shaped laser pulse. Continuum radiation emitted in the core is transmitted through the tracer layer and the resulting spectrum recorded with a gated multi-monochromatic x-ray imager (MMI). Titanium K-shell line absorption spectra observed in the data are due to transitions in L-shell titanium ions driven by the backlighting continuum. The MMI data consist of an array of spectrally resolved images of the implosion. These 2-D space-resolved titanium spectral features constrain the plasma conditions and areal density of the titanium doped region of the shell. The MMI data were processed to obtain narrow-band images and space resolved spectra of titanium spectral features. Shell areal density maps, ρL(x,y), extracted using a new method using both narrow-band images and space resolved spectra are confirmed to be consistent within uncertainties. We report plasma conditions in the titanium-doped region of electron temperature (T e ) = 400±28eV, electron number density (N e ) = 8.5x10 24 ±2.5x10 24 cm -3 , and average areal density <ρR> = 86±7mg/cm 2 . Fourier analysis of areal density maps reveals shell modulations caused by hydrodynamic instability growth near the fuel-shell interface in the deceleration phase. We observe significant structure in modes l = 2-9, dominated by l = 2. We extract a target breakup fraction of 7.1±1.5% from our Fourier analysis. A new method for estimating mix width is evaluated against existing literature and our target breakup fraction. We estimate a mix width of 10.5±1μm.
Transformation of metallic or bimetallic (BM) nanoparticles (NPs) from one shape to another desired shape is of importance to nanoscience and nanotechnology, where new morphologies of NPs lead to enhancement of their exploitable properties. In this report, we present the shape transformation of Au octahedral NPs to Au–Pd core–shell nanocubes, followed by their transformation to nanostars and finally to multilayered Au–Pd–Au core–shell hexagonal platelets in the presence of T30 DNA. The weaker binding affinity of T30 DNA directs the growth to favor the formation of lower energy {111} facets, changing the morphology from nanocubes to nanostar. The nanostars, exhibiting unusual intermediate morphologies, are comprised two sets of shell layers and have Au core, Pd intermediate shell, and Au outer shell. Similarly, the hexagonal platelets, which also have Au core and inner Pd shell, are encased in an external gold shell. As a result, the formation of multilayered Au–Pd–Au core–shell hexagonal platelets from Au–Pd core–shell nanocubes via the multilayered nanostars is monitored using scanning/transmission electron microscopy analysis.
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We reported the preparation of C@Ni–NiO core–shell hybrid solid spheres or multi-shelled NiO hollow spheres by combining a facile hydrothermal route with a calcination process in H{sub 2} or air atmosphere, respectively. The synthesized C@Ni–NiO core–shell solid spheres with diameters of approximately 2–6 μm were in fact built from dense NiO nanoparticles coated by random two-dimensional metal Ni nanosheets without any visible pores. The multi-shelled NiO hollow spheres were built from particle-like ligaments and there are a lot of pores with size of several nanometers on the surface. Combined Raman spectra with X-ray photoelectron spectra (XPS), it suggested that the defects in the samples play a limited role in the dielectric loss. Compared with the other samples, the permeability of the samples calcined in H{sub 2} and air was increased slightly and the natural resonance frequency shifted to higher frequency (7, 11 and 14 GHz, respectively), leading to an enhancement of microwave absorption property. For the sample calcined in H{sub 2}, an optimal reflection loss less than − 10 was obtained at 7 GHz with a matching thickness of 5.0 mm. Our study demonstrated the potential application of C@Ni–NiO core–shell hybrid solid sphere or multi-shelled NiO hollow sphere as a more efficient electromagnetic (EM) wave absorber. - Highlights: • C@Ni–NiO core–shell hybrid solid sphere was synthesized by a facile method. • Multi-shelled NiO hollow sphere was synthesized by a facile method. • It suggested that the defects in the samples play a limited role in dielectric loss. • The permeability of the samples calcined in H{sub 2} and air was increased. • Microwave absorbability of C@Ni–NiO core–shell hybrid solid sphere was investigated.
Bacterial microcompartments are subcellular compartments found in many prokaryotes; they consist of a protein shell that encapsulates enzymes that perform a variety of functions. The shell protects the cell from potentially toxic intermediates and co-localizes enzymes for higher efficiency. Accordingly, it is of considerable interest for biotechnological applications. We have previously structurally characterized an intact 40 nm shell comprised of three different types of proteins. One of those proteins, BMC-H, forms a cyclic hexamer; here we have engineered a synthetic protein that consists of a tandem duplication of BMC-H connected by a short linker. The synthetic protein forms cyclic trimers that self-assemble to form a smaller (25 nm) icosahedral shell with gaps at the pentamer positions. When co-expressed in vivo with the pentamer fused to an affinity tag we can purify complete icosahedral shells. This engineered shell protein constitutes a minimal shell system to study permeability; reducing symmetry from six- to three-fold will allow for finer control of the pore environment. In conclusion, we have determined a crystal structure of this shell to guide rational engineering of this microcompartment shell for biotechnological applications.