Multifactor-Controlled Non-Monotonic Plasmon Shift of Ordered Gold Nanodisk Arrays: Shape-Dependent Interparticle Coupling

Surface plasmon resonance (SPR) absorption spectra of gold nanodisks hexagonally arranged in planar arrays have been studied by using coupled dipole method and quasi-static approximation. The calculation results reveal that the increasing aspect ratio (AR) of gold disks in the close-packed nanoarray leads to SPR blue shift firstly and then red shift. The critical AR corresponding to the maximum blue shift can be controlled by tuning the interparticle distance and particle size. The physical mechanism of this non-monotonic SPR shift is investigated based on the competition between the influences from shape factor and arranging structure of the array. Although increasing the semi-minor axis of gold disk reduces the AR and leads to a blue shift of SPR, this increasing semi-minor axis also reduces the average gap between two neighboring disks and enhances their coupling. Furthermore, the coulombic attraction between two neighboring disks introduces an additional plasmon damping and results in a red shift of SPR. This competition between AR and interparticle coupling improves the tuning ability of SPR in anisotropic metallic nanoparticle arrays and presents a potential for design and fabrication of optical biochip based on SPR.     

In Situ Monitoring of the 2D Aggregation Process of Thiol-Coated Gold Nanoparticles Using Interparticle Plasmon Coupling

Near-field plasmon coupling between neighboring gold nanoparticles, measured by polarized optical waveguide lightmode spectroscopy, is employed to study the surface self-assembly of alcanethiol-capped gold nanoparticles during solvent evaporation. The waveguide used is a monomode optical fiber half-coupler. The sample is deposited on the surface of the waveguide and absorption spectra are continuously collected during the solvent evaporation process with a temporal resolution of 0.2 s. The absorption spectra show a progressive red shift of the plasmon peak caused by increasing interparticle near-field coupling. This shift can be used to determine the distance between particles by comparison to theoretical values calculated using the discrete dipoles approximation. The technique is demonstrated for the assembly of 10 nm gold particles capped with thiol ligands of two different lengths. Interestingly, in the case of dodecanethiol-capped particles, the extinction spectrum not only shifts to longer wavelengths, but also changes in shape during the drying process. About half a second before the solvent completely evaporates, the spectrum broadens as a second component appears. This feature is tentatively attributed to the formation of a significant population of particle clusters as a result of incomplete screening of van der Waals attractions by the shorter ligand.     

The Plasmon–Plasmon Coupling in a System of a Dielectric Slab Doped with Silver Nano-spheres Sandwiched Between Two Silver Parallel Plates

I compute the transmission coefficient as function of the incident light frequency for a system consisting of a dielectric slab doped with silver nano-spheres sandwiched between two silver parallel plates. Then, I analyze the details of the transmission spectrum identifying the coupled plasmons from the two (doped dielectric and plates) subsystems which dominate the system’s dynamics.     

Surface Plasmon Resonance Field-Enhanced Fluorescence Properties of Gold Quantum Dots on Polyelectrolyte Multilayers and Their H2O2 Sensor Application

Plasmonics - In this work, we investigate surface plasmon field-enhanced fluorescence (SPF) emission from gold quantum dots (AuQDs) on a polyelectrolyte multilayer ultrathin film deposited onto an...     

Coherent Controllable Transport of a Surface Plasmon Coupled to a Plasmonic Waveguide with a Metal Nanoparticle-Semiconductor Quantum Dot Hybrid System

Plasmonics - By using the real-space method, the switching of a single plasmon interacting with a hybrid nanosystem composed of a semiconductor quantum dot (SQD) and a metallic nanoparticle (MNP)...     

Entanglement of Two Quantum Dots with Azimuthal Angle Difference in Plasmonic Waveguide System

We investigate the properties of entanglement between two quantum dots (QDs) with an azimuthal angle difference in two different plasmonic waveguide systems where a cavity coupled to the QDs is included or not. The real space formalism and the concurrence are used in solving the eigenvalue equation and calculating the entanglement, respectively. We analyze the influence of azimuthal angle difference on the entanglement and propose several effective ways to achieve high entanglement by adjusting the detuning, the QD-cavity coupling strength, and so on. Moreover, comparing the entanglement in the two models, we demonstrate that the addition of cavity can improve the entanglement of two QDs.

     

Coupling Behaviors of Surface Plasmon Polariton and Localized Surface Plasmon with an InGaN/GaN Quantum Well

Plasmonics - Surface plasmon (SP) coupling behaviors of an InGaN/GaN quantum well (QW) with surface plasmon polariton (SPP) induced on a smooth Ag-film/GaN interface and localized surface plasmon...     

Effects of Surface Plasmon Coupling on the Whispering-Gallery Resonance in a Hexagonal Nanowire Cavity Structure

Plasmonics - The effects of surface plasmon (SP) coupling with the excitation radiating dipole on the behaviors of the whispering-gallery resonance (WGR) modes in a hexagonal GaN nanowire cavity...     

Effects of Multiple Occupancy and Interparticle Interactions on Selective Transport through Narrow Channels: Theory versus Experiment

Many biological and artificial transport channels function without direct input of metabolic energy during a transport event and without structural rearrangements involving transitions from a closed to an open state. Nevertheless, such channels are able to maintain efficient and selective transport. It has been proposed that attractive interactions between the transported molecules and the channel can increase the transport efficiency and that the selectivity of such channels can be based on the strength of the interaction of the specifically transported molecules with the channel. Herein, we study the transport through narrow channels in a framework of a general kinetic theory, which naturally incorporates multiparticle occupancy of the channel and non-single-file transport. We study how the transport efficiency and the probability of translocation through the channel are affected by interparticle interactions in the confined space inside the channel, and establish conditions for selective transport. We compare the predictions of the model with the available experimental data and find good semiquantitative agreement. Finally, we discuss applications of the theory to the design of artificial nanomolecular sieves.     

Modification of Spontaneous Emission Rates of Self-assembled CdSe Quantum Dots by Coupling to Hybrid Optical Nanoantennas

Plasmonics - The spontaneous emission of a light source can be modified by tailoring its local density of optical states. Indeed, this concept has been commonly utilized to enhance the spontaneous...     

含镉量子点的毒性研究进展

含镉量子点是典型的量子点,近年来受到广泛研究。含镉量子点的潜在毒性是其在生物成像及生物医药方面应用和发展的关键制约因素,因此,对其毒性作用的研究具有重要意义。目前对含镉量子点的体外毒性研究主要集中在人肝癌细胞(HepG2)、神经分泌细胞(PC12)等细胞实验及斑马鱼胚胎体外培养实验。体内毒性研究包括小鼠等动物实验。这些研究证实,量子点对HepG2等细胞系和小鼠、贻贝等动物均具细胞毒性。研究者们普遍认为,量子点是通过释放其组成中的重金属,诱导生物体产生活性氧自由基,进而引发细胞凋亡或自噬,但对量子点的具体毒性作用机制并不完全清楚。该文对含镉量子点的体内和体外毒性研究工作进展进行了综述,包括含镉量子点对肝肾细胞、神经细胞、血液细胞及免疫细胞等体外毒性研究工作,对陆生及水生动物等的体内毒性研究工作,旨在更好、更全面地评估含镉量子点的毒性,为今后对量子点的毒性作用机制研究提供方向,促进含镉量子点在生物医学方面的发展和应用。     

Quantum Dots as a Novel Immunofluorescent Detection System for Cryptosporidium parvum and Giardia lamblia

Semiconductor quantum dot-conjugated antibodies were successfully developed to label Cryptosporidium parvum and Giardia lamblia. This novel fluorescence system exhibited superior photostability, gave 1.5- to 9-fold-higher signal-to-noise ratios than traditional organic dyes in detecting C. parvum, and allowed dual-color detection for C. parvum and G. lamblia.     

Enhancement of Emission Efficiency of Deep-Ultraviolet AlGaN Quantum Wells Through Surface Plasmon Coupling with an Al Nanograting Structure

The enhancement of the internal quantum efficiency (IQE) of deep-ultraviolet Al _x Ga_1-x N/Al _y Ga_1-y N (x < y) quantum wells (QWs) by fabricating one-dimensional Al nanogratings on a QW structure for inducing surface plasmon (SP) coupling is demonstrated. Through temperature-dependent photoluminescence (PL) measurement, the enhancements of IQE in different emission polarizations are illustrated. Due to the small difference in energy band level between the heavy/light hole and split-off valence bands, the IQEs of the transverse electric- (TE-) and transverse magnetic- (TM-) polarized emissions are about the same. When emission polarization is perpendicular to Al-grating ridges, the SP resonance mode for coupling with the QWs is dominated by localized surface plasmon (LSP). When emission polarization is parallel with Al-grating ridges, the coupled SP resonance mode may mix LSP and SP polariton. In this polarization, LSP can be excited because of the width fluctuation of a grating ridge. When the excitation laser polarization is perpendicular to Al-grating ridges, the strong LSP resonance at the excitation laser wavelength leads to stronger excitation and hence higher IQE levels.     

Ring Gap Resonance Modes on Disk/Film Coupling System Caused by Strong Plasmon Interaction

Ring modes with large wave vectors cannot be easily excited on a single disk by the plane wave illumination with the polarization parallel to the disk interface. In this work, we show that special antisymmetric ring gap modes on the surface of the disk in close proximity to the metallic thin film can be excited in the visible light region of the electromagnetic spectrum. In the presence of the film, the strong plasmon interaction between disk and film causes ring gap modes to have lower energies and be more easily excited. We apply the plasmon hybridization method to illustrate the ring gap modes arising from the interaction between the localized disk plasmons and the continuum surface plasmons. The calculated hybridization data show good agreement with the results of finite element simulations. The excitation of ring gap modes provides further insight into the strong coupling of plasmons and the design of novel nanostructures.

     

Transport Properties of Melanosomes along Microtubules Interpreted by a Tug-of-War Model with Loose Mechanical Coupling

In this work, we explored theoretically the transport of organelles driven along microtubules by molecular motors of opposed polarities using a stochastic model that considers a Langevin dynamics for the cargo, independent cargo-motor linkers and stepping motion for the motors. It has been recently proposed that the stiffness of the motor plays an important role when multiple motors collectively transport a cargo. Therefore, we considered in our model the recently reported values for the stiffness of the cargo-motor linker determined in living cells (～0.01 pN/nm, [1]) which is significantly lower than the motor stiffness obtained in in vitro assays and used in previous studies. Our model could reproduce the multimodal velocity distributions and typical trajectory characteristics including the properties of the reversions in the overall direction of motion observed during melanosome transport along microtubules in Xenopus laevis melanophores. Moreover, we explored the contribution of the different motility states of the cargo-motor system to the different modes of the velocity distributions and could identify the microscopic mechanisms of transport leading to trajectories compatible with those observed in living cells. Finally, by changing the attachment and detachment rates, the model could reproduce the different velocity distributions observed during melanosome transport along microtubules in Xenopus laevis melanophores stimulated for aggregation and dispersion. Our analysis suggests that active tug-of-war processes with loose mechanical coupling can account for several aspects of cargo transport along microtubules in living cells.     

Synchronization of Two Homodromy Rotors Installed on a Double Vibro-Body in a Coupling Vibration System

A new mechanism is proposed to implement synchronization of the two unbalanced rotors in a vibration system, which consists of a double vibro-body, two induction motors and spring foundations. The coupling relationship between the vibro-bodies is ascertained with the Laplace transformation method for the dynamics equation of the system obtained with the Lagrange’s equation. An analytical approach, the average method of modified small parameters, is employed to study the synchronization characteristics between the two unbalanced rotors, which is converted into that of existence and the stability of zero solutions for the non-dimensional differential equations of the angular velocity disturbance parameters. By assuming the disturbance parameters that infinitely approach to zero, the synchronization condition for the two rotors is obtained. It indicated that the absolute value of the residual torque between the two motors should be equal to or less than the maximum of their coupling torques. Meanwhile, the stability criterion of synchronization is derived with the Routh-Hurwitz method, and the region of the stable phase difference is confirmed. At last, computer simulations are preformed to verify the correctness of the approximate solution of the theoretical computation for the stable phase difference between the two unbalanced rotors, and the results of theoretical computation is in accordance with that of computer simulations. To sum up, only the parameters of the vibration system satisfy the synchronization condition and the stability criterion of the synchronization, the two unbalanced rotors can implement the synchronization operation.     

Feasible Surface Plasmon Routing Based on the Self-Assembled InGaAs/GaAs Semiconductor Quantum Dot Located Between Two Silver Metallic Waveguides

Plasmonics - We proposed an experimentally feasible scheme of nano-plasmonic switch and quantum router via the single self-assembled InGaAs/GaAs semiconductor quantum dot (SQD) with a V-type...     

Surface Plasmon Coupling Effect of Gold Nanoparticles with Different Shape and Size on Conventional Surface Plasmon Resonance Signal

The labeling strategy with gold nanoparticles for the conventional surface plasmon resonance (SPR) signal enhancement has been frequently used for the sensitive determination of small molecules binding to its interaction partners. However, the influence of gold nanoparticles with different size and shape on SPR signal is not known. In this paper, three kinds of gold nanoparticles, namely nanorods, nanospheres, and nanooctahedrons with different size, were prepared and used to investigate their effects on the conventional SPR signal at a fixed excitation wavelength 670 nm. It was found that the SPR signal (i.e., resonant angle shift) was varied with the shapes and sizes of gold nanoparticles in suspension at a fixed concentration due to their different plasmon absorbance bands. For gold nanorods with different longitudinal absorbance bands, three conventional SPR signal regions could be clearly observed when the gold nanorod suspensions were separately introduced onto the SPR sensor chip surface. One region was the longitudinal absorbance bands coinciding with or close to the SPR excitation wavelength that suppressed the SPR angle shift. The second region was the longitudinal absorbance bands at 624 to 639 and 728 to 763 nm that produced a moderate increase on the SPR resonant angle shift. The third region was found for the longitudinal absorbance bands from 700 to 726 nm that resulted in a remarkable increase in the SPR angle shift responses. This phenomenon can be explained on the basis of calculation of the correlation of SPR angle shift response with the gold nanorod longitudinal absorbance bands. For nanospheres and nanooctahedrons, the SPR angle shift responses were found to be particle shape and size dependent in a simple way with a sustaining increase when the sizes of the nanoparticles were increased. Consequently, a guideline for choosing gold nanoparticles as tags is suggested for the SPR determination of small molecules with binding to the immobilized interaction partners.     

Phenomenon of Quantum Entanglement in a System Composed of Two Minimal Protocells

The quantum mechanical self-assembly of two separate photoactive supramolecular systems with different photosynthetic centers was investigated by means of density functional theory methods. Quantum entangled energy transitions from one subsystem to the other and the assembly of logically controlled artificial minimal protocells were modeled. The systems studied were based on different photoactive sensitizer molecules covalently bonded to a non-canonical oxo-guanine::cytosine supramolecule with the precursor of a fatty acid (pFA) molecule attached via Van der Waals forces, all surrounded by water molecules. The electron correlation interactions responsible for the weak hydrogen and Van der Waals chemical bonds increased due to the addition of polar water solvent molecules. The distances between the separated sensitizer, nucleotide, pFA, and water molecules are comparable to Van der Waals and hydrogen bonding radii. As a result, the overall system becomes compressed, resulting in photo-excited electron tunneling from the sensitizer (bis(4-diphenylamine-2-phenyl)-squarine or 1,4-bis(N,N-dimethylamino)naphthalene) to the pFA molecules. Absorption spectra as well as electron transfer trajectories associated with the different excited states were calculated using time dependent density functional theory methods. The results allow separation of the quantum entangled photosynthetic transitions within the same minimal protocell and with the neighboring minimal protocell. The transferred electron is used to cleave a “waste” organic molecule resulting in the formation of the desired product. A two variable, quantum entangled AND logic gate was proposed, consisting of two input photoactive sensitizer molecules and one output (pFA molecule). It is proposed that a similar process might be applied for the destruction of tumor cancer cells or to yield building blocks in artificial cells.