The localized surface-plasmon resonance has drawn great attention, due to its unique optical properties. In this work a general theoretical description of the dipole mode is proposed, using the ...forced damped harmonic oscillator model of free charges in an ellipsoid. The restoring force and driving force are derived in the quasistatic approximation under general conditions. In this model, metal is regarded as composed of free charges and bound charges. The bound charges form the dielectric background which has a dielectric function. Those free charges undergo a collective motion in the dielectric background under the driving force. The response of free charges will not be included in the dielectric function like the Drude model. The extinction and scattering cross sections as well as the damping coefficient from our model are verified to be consistent with those based on the Drude model. We introduce size effects and modify the restoring and driving forces by adding the dynamic depolarization factor and the radiation damping term to the depolarization factor. This model provides an intuitive physical picture as well as a simple theoretical description of the dipole mode of the localized surface-plasmon resonance based on free-charge collective motion.
Early, sensitive, and reproducible evaluation of left ventricular function is imperative for the diagnosis of cardiac dysfunction in patients with Duchene muscular dystrophy. The aim of this study ...was to test the hypothesis that combining two-dimensional strain analysis with catecholamine stress could be a sensitive method for detecting early cardiac dysfunction.
Mdx (C57BL/10ScSn-Dmdmdx/J, a mouse model of DMD) and control (C57BL/10ScSn) mice were studied with conventional M-mode and high-frequency ultrasound-based two-dimensional speckle-tracking echocardiography using long- and short-axis images of the left ventricle at baseline and after intraperitoneal isoprenaline (ISO) administration (2 μg/g body weight).
Conventional M-mode analysis showed no differences in left ventricular fractional shortening, wall thickness, or internal diameter at diastole between mdx and control mice before the age of 6 months. ISO increased left ventricular ejection fraction and fractional shortening to the same extent in mdx and control mice at young ages (3, 4, and 5 months). No differences in basal peak systolic strain (PSS) but increased SDs of times to PSS between young mdx and control mice were found. After ISO, PSS and percentile changes of PSS were significantly diminished in mdx mice compared with control mice at young ages. ISO increased the normalized maximum difference of times to PSS in young mdx mice but not in young control mice, suggesting that ISO reduces cardiac contractile synchrony in young mdx mice.
This study suggests that catecholamine stress coupled with two-dimensional strain analysis is a feasible and sensitive approach for detecting early onset of cardiac dysfunction, which is instrumental for early diagnosis of cardiac dysfunction and early treatment.
Novel TiO₂/Sn₃O₄ heterostructure photocatalysts were ingeniously synthesized via a scalable two-step method. The impressive photocatalytic abilities of the TiO₂/Sn₃O₄ sphere nanocomposites were ...validated by the degradation test of methyl orange and •OH trapping photoluminescence experiments under ultraviolet (UV) and visible light irradiation, respectively. Especially under the visible light, the TiO₂/Sn₃O₄ nanocomposites demonstrated a superb photocatalytic activity, with 81.2% of methyl orange (MO) decomposed at 30 min after irradiation, which greatly exceeded that of the P25 (13.4%), TiO₂ (0.5%) and pure Sn₃O₄ (59.1%) nanostructures. This enhanced photocatalytic performance could be attributed to the mesopore induced by the monodispersed TiO₂ cores that supply sufficient surface areas and accessibility to reactant molecules. This exquisite hetero-architecture facilitates extended UV-visible absorption and efficient photoexcited charge carrier separation.
Bonding and anti-bonding modes of plasmon coupling effects are numerically investigated in TiO2-Ag core-shell nano dimers. First, splitting phenomena of the coupled anti-bonding modes are observed ...under the longitudinal polarization when the distance between the monomers decreases to a certain level. Second, one of the split resonance modes is identified to be formed by the dipole anti-bonding mode of the monomers from charge density distribution patterns. Those split modes have similar redshift behaviors as the coupled dipole bonding modes in the same situations. Furthermore, the intensities of those anti-bonding modes weaken with decreasing distance between the monomers, because of the interaction of the induced dipole moment in the monomers and the charge distribution variation on the facing surfaces of the gap by the coulomb attraction. Other split bands are the higher-order mode (octupole-like or triakontadipole-like), which do not have obvious peak-shift behavior, and the intensities have very little attenuation with decreasing distance. Finally, the coupling of the bonding and anti-bonding modes under the longitudinal polarization is symmetric (bonding).
Two-dimensional (2D) MXenes are attractive candidates as surface-enhanced Raman scattering (SERS) substrates because of their metallic conductivity and abundant surface terminations. Herein, we ...report the facile synthesis of bimetallic solid-solution TiVC (MXene) and its application in SERS. The few-layered MXene nanosheets with high crystallinity were successfully prepared using a one-step chemical etching method without ultrasonic and organic solvent intercalation steps. SERS activity of the as-prepared MXene was investigated by fabricating free-standing TiVC film as the substrate. A SERS enhancement factor of 1012 and femtomolar-level detection limit were confirmed using rhodamine 6G as a model dye with 532 nm excitation. The fluorescent signal of the rhodamine 6G dye was effectively quenched, making the SERS spectrum clearly distinguishable. Furthermore, we demonstrate that the TiVC-analyte system with ultrahigh sensitivity is dominated by the chemical mechanism (CM) based on the experimental and simulation results. The abundant density of states near the Fermi level of the TiVC and the strong interaction between the TiVC and analyte promote the intermolecular charge transfer resonance in the TiVC–analyte complex, resulting in significant Raman enhancement. Additionally, several other probe molecules were used for SERS detection to further verify CM-based selectivity enhancement on the TiVC substrates. This work provides guidance for the facile synthesis of 2D MXene and its application in ultrasensitive SERS detection.
A forced damped harmonic oscillator model of the dipole plasmon mode is illustrated by the theoretical derivation and the simulation based on the metal ellipsoids. The analytical expression of the ...restoring force is derived. The displacement of the oscillator, which is the phenomenological relative displacement of the free negative and positive charge systems in solids, can be represented by the accumulated charges on the surface of the nanoparticles based on the derived results. With the help of the finite-difference time-domain method, the dependence of the resonance wavelengths and the surface charge distributions on the geometric parameters and the materials has been verified by the ellipsoids evolved from 10 nm radius spheres. As an essential feature of an oscillator, the phase shifts, which are between the accumulated surface charges (the displacement of the oscillator) and the electric field of the incident light, are also illustrated by the numerical simulation. For the silver nanoparticle with the radius of 10 nm, the phase shifts are consistent with the feature of a forced damped harmonic oscillator. For the large silver nanoparticle with the radius of 50 nm, the magnitudes of the phase shifts have some deviations due to the nonuniform electric field along the light propagation. By this oscillator model, we confirm that localized surface plasmon resonance arises from the collective motion of free charges modulated by the bound charges of the lattice background and the dielectric medium. The forced damped harmonic oscillator model is a clear picture for the dipole localized surface plasmon resonance.
Over the last decade safety concerns have arisen about the use of metal-based nanoparticles in the cosmetics field. Metal-based nanoparticles have been linked to both environmental and animal ...toxicity in a variety of studies. Perhaps the greatest concern involves the large amounts of TiO2 nanoparticles that are used in commercial sunscreens. As an alternative to using these potentially hazardous metal-based nanoparticles, we have isolated organic nanoparticles from English ivy (Hedera helix). In this study, ivy nanoparticles were evaluated for their potential use in sunscreens based on four criteria: 1) ability to absorb and scatter ultraviolet light, 2) toxicity to mammalian cells, 3) biodegradability, and 4) potential for diffusion through skin.
Purified ivy nanoparticles were first tested for their UV protective effects using a standard spectrophotometric assay. Next the cell toxicity of the ivy nanoparticles was compared to TiO2 nanoparticles using HeLa cells. The biodegradability of these nanoparticles was also determined through several digestion techniques. Finally, a mathematical model was developed to determine the potential for ivy nanoparticles to penetrate through human skin. The results indicated that the ivy nanoparticles were more efficient in blocking UV light, less toxic to mammalian cells, easily biodegradable, and had a limited potential to penetrate through human skin. When compared to TiO2 nanoparticles, the ivy nanoparticles showed decreased cell toxicity, and were easily degradable, indicating that they provided a safer alternative to these nanoparticles.
With the data collected from this study, we have demonstrated the great potential of ivy nanoparticles as a sunscreen protective agent, and their increased safety over commonly used metal oxide nanoparticles.
Flower-like SnO2 porous microspheres self-assembled by hollow nanospheres have been successfully synthesized via a sucrose-assisted solvothermal method. The morphology, structure and composition of ...the as-prepared product have been characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) with selected area electron diffraction (SAED) and X-ray diffraction (XRD). The results show that the microspheres are self-assembled completely by well-defined SnO2 hollow nanospheres with porous wall composed of single crystalline nanoparticles. A growth mechanism has been proposed to explain the growth processes for such novel structures. First ever study on hydrogen absorption characteristics of the flower-like SnO2 microspheres performed at 373K shows a good absorption capacity of 0.92wt%.
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•Flower-like SnO2 porous microspheres have been successfully synthesized by sucrose-assisted solvothermal synthesis.•The growth mechanism for such novel structure is attributed to the self-assembly of prime hollow nanospheres.•The novel structure shows a good hydrogen absorption capacity of 0.92wt%.
Sn3O4/BiOX (X = Cl, Br, I), a series of p–n-heterojunction-based photocatalysts, were prepared by a combination of an ultrasonic-assisted precipitation–deposition method and hydrothermal method. The ...photodegradation of Rhodamine B among all the materials, under simulated solar light irradiation, was investigated in detail. The photocatalyst test showed that the novel composite, Sn3O4/BiOCl, was able to degrade 99% of Rhodamine B (RhB) and its intermediates in 9 minutes, which is faster than Sn3O4/BiOBr (21 min) and Sn3O4/BiOI (12 min). Moreover, the degradation rate of RhB for Sn3O4/BiOCl samples (Sn : Bi = 1/4) was the highest, about 99%, slightly higher than that of Sn3O4/BiOCl-1/8 (95%), which was significantly higher than those of Sn3O4/BiOCl-1/2 (78%), BiOCl (77%), P25 (62%) and Sn3O4 (16%) after nine minutes of irradiation under a xenon lamp. It can be inferred that when the bismuth/tin ratio was optimum, BiOCl enabled the formation of the enough space charge regions on the surface of Sn3O4, which promoted the separation of photogenerated electron–hole pairs. This implied that high-quality interfaces in the heterostructure catalysts play a key role in improving the photocatalytic performance. The enhanced photocatalytic performance can be attributed to the synergistic effects from two main factors: (1) the layered multi-stage structure increases the scattering of light on the catalyst surface, which proves to be beneficial in enhancing the absorption of the visible light; (2) the p–n heterojunctions between Sn3O4 and BiOX (X = Cl, Br, I) efficiently promote the separation of photogenerated carriers and accelerate the migration of photogenerated carriers. In addition, the results of the ‘active species trapping’ experiment illustrated that in the Sn3O4/BiOCl composite, holes contribute more to the high photocatalytic performance, while hydroxyl radicals show less importance to degrade RhB. Moreover, the photocatalytic mechanism was also discussed based on the investigation of reactive species and the band structure of Sn3O4/BiOCl.
The localized surface-plasmon resonance has drawn great attention, due to its unique optical properties. In this work a general theoretical description of the dipole mode is proposed, using the ...forced damped harmonic oscillator model of free charges in an ellipsoid. The restoring force and driving force are derived in the quasistatic approximation under general conditions. In this model, metal is regarded as composed of free charges and bound charges. The bound charges form the dielectric background which has a dielectric function. Those free charges undergo a collective motion in the dielectric background under the driving force. The response of free charges will not be included in the dielectric function like the Drude model. The extinction and scattering cross sections as well as the damping coefficient from our model are verified to be consistent with those based on the Drude model. We introduce size effects and modify the restoring and driving forces by adding the dynamic depolarization factor and the radiation damping term to the depolarization factor. This model provides an intuitive physical picture as well as a simple theoretical description of the dipole mode of the localized surface-plasmon resonance based on free-charge collective motion.
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