SiO_2/Ag核壳结构纳米粒子的制备及其表面荧光增强

以罗丹明B掺杂的SiO2球为核,通过化学还原的方法制备了二氧化硅/银核壳结构复合纳米粒子。采用透射电镜(TEM)、紫外-可见-近红外(UV-Vis-NIR)分光光度计和荧光分光光度计对二氧化硅/银核壳结构纳米粒子的表面形貌、表面等离子共振和表面荧光增强特性进行了研究和表征。结果表明,二氧化硅/银核壳结构纳米粒子的表面等离子共振峰具有明显的可调谐性,且其表面荧光增强强烈依赖于银壳层的表面等离子共振,随银壳层厚度的增大而增强。     

Integrated localized surface plasmon waveguides

Compact plasmonic structures made of gold nanoparticles chains are inserted on silicon optical waveguides. We show that silicon-on-insulator waveguide TE mode energy can be almost totally transferred in a 5 gold nanoparticles plasmonic chain, and that this short chain can also behave as a waveguide.     

Charge transfer between sensing and targeted metal nanoparticles in indirect nanoplasmonic sensors

In indirect nanoplasmonic sensors, the plasmonic metal nanoparticles are adjacent to the material of interest, and the material-related changes of their optical properties are used to probe that material. If the latter itself represents another metal in the form of nanoparticles, its deposition is accompanied by charge transfer to or from the plasmonic nanoparticles in order to equalize the Fermi levels. We estimate the value of the transferred charge and show on the two examples, nanoparticle sintering and hydride formation, that the charge transfer has negligible influence on the probed processes, because the effect of charge transfer is less important than that of nanoparticle surface energy. This further corroborates the non-invasive nature of nanoplasmonic sensors.     

Silver nanoparticle size–dependent measurement of quantum efficiency of Rhodamine 6G

The plasmonic absorption band of silver nanoparticles in the visible range of electromagnetic spectrum has been successfully exploited to alter the emission characteristics of the Rhodamine 6G dye molecule. The influence of the nanoparticle size on the fluorescence quantum yield of Rhodamine 6G is interrogated via steady state fluorescence as well as dual beam thermal lens technique. The potential of the thermal lens technique that probe nonradiative path in contrast to radiative path exhibited in the fluorescence spectra as a complementary method to measure the quantum yield of a dye molecule is exploited. Analysis of the results clearly indicates that the particle size and the spectral overlap between the emission spectra of Rhodamine 6G, and absorption spectra of the silver nanoparticles determine the quantum yield value of dye–nanoparticle mixture.     

Two‐Photon Imaging of a Cellular Line Using Organic Fluorescent Nanoparticles Synthesized by Laser Ablation

A comparative study of the optical properties of organic fluorescent nanoparticles fabricated by laser ablation (NPs‐LA), reprecipitation (NPs‐RP), and microemulsion (NPs‐ME) methods is presented. These nanoparticles contain a fluorene‐based p‐conjugated molecule (BT2). Distinctive electronic transitions are observed in samples due to the specific way in which the molecule BT2 is assembled in each type of nanoparticles; for instance, transitions involved in absorption and emission spectra of NPs‐LA result in blueshifting with respect to the molecular solution of BT2, whereas redshifting is observed in NPs‐RP and NPs‐ME. Further, the results show that under infrared excitation, the aqueous suspensions of NPs‐LA exhibit the highest fluorescence induced by two‐photon absorption (≈790 GM at 740 nm), as well as the best photostability, compared with aqueous suspensions of NPs‐RP and NPs‐ME. The nanoparticles synthetized by the three aforementioned methods are employed as exogenous agents for the visualization of human cervical cancer cell line (HeLa) using confocal and two‐photon microscopy. Under similar experimental conditions, it is found that microscopy images of the best quality are obtained with NPs‐LA. These results show that laser ablation is a suitable technique for the fabrication of organic fluorescent nanoparticles used as contrast agents for in vitro fluorescence microscopy.     

光解水的原子尺度机理和量子动力学

利用阳光直接将水分解为不含碳的氢气燃料和氧气是面向全球能源危机环保且低成本的解决方案.得益于电子结构理论和量子模拟方法的进步,人们已经能够直接研究在纳米颗粒上等离激元诱导光解水过程在原子尺度上的反应机理和超快动力学.本文简述近年来的相关工作进展.吸附在氧化物薄膜上的金纳米颗粒很有希望成为水分解的高效新型光催化剂.在光激发条件下,水分解反应速率和光强、热电子转移之间有强相关性.水分解速率不仅取决于光吸收强度,还受到等离激元量子振动模式的调控.这对于太阳能光解水器件中纳米颗粒的设计有借鉴意义.我们发现液态水在金团簇等离激元催化下100 fs内就能产生氢气.超快量子动力学模拟表明,该过程中场增强起主导作用,从金属到水反键态的超快电荷转移也扮演着重要角色.综合这些原子尺度上的量子动力学研究,我们提出受激水分子中氢原子高速碰撞(速度远远超出其热速度)合成氢分子的"链式反应"机理.     

Plasmon-induced transparency in metamaterials

A plasmonic "molecule" consisting of a radiative element coupled with a subradiant (dark) element is theoretically investigated. The plasmonic molecule shows electromagnetic response that closely resembles the electromagnetically induced transparency in an atomic system. Because of its subwavelength dimension, this electromagnetically induced transparency-like molecule can be used as a building block to construct a "slow light" plasmonic metamaterial.     

Magnetic separation and SERS observation of analyte molecules on bifunctional silver/iron oxide composite nanostructures

We report the preparation of bifunctional silver–iron oxide composite nanostructures (Ag@Fe₂O₃) and demonstrate their magnetic separation with an analyte molecule from silver nanoparticles in a mixed solution. Magnetic and non‐magnetic plasmonic nanostructures and their separation are monitored by the surface‐enhanced Raman scattering (SERS) spectra of two different analytes attached to each kind of particles. In general, such separation experiments can provide insight into basic phenomena of adsorption and exchange of adsorbed molecules which are of strong interest in SERS. The formation of stable Ag@Fe₂O₃ nanoparticle–molecule complexes suggests small magnetic SERS labels without additional protective layers for application in analytical assays. The magnetic plasmonic nanostructures have great promise for targeted imaging and sensing in biological structures by directing nanosensors to places of interest using magnetic fields. The option of magnetic separation and collection of plasmonic particles improves the analytical capabilities of SERS. Copyright © 2012 John Wiley & Sons, Ltd.     

Enhancement of Optical Second Harmonic Generation in Hybrid Plasmonic–Photonic Microcavities

A one-dimensional combined plasmonic–photonic system tailored for the enhancement of nonlinear optical effects is proposed and implemented. In this structure, a layer of silver plasmonic nanoparticles is placed in the cavity region of a photonic-crystal microcavity made of porous silicon. A multifold increase in an optical second harmonic generation signal in comparison to the structure without plasmonic nanoparticles is demonstrated.     

Surface plasmon resonance in near-field coupled gold cylinder arrays fabricated by EUV-interference lithography and hot embossing

Arrays of metal nanoparticles with nanometer-scale gaps between the particles is highly interesting for plasmonic field enhancement applications. We report a simple method to fabricate arrays of closely spaced Au particles with inter-particle separation down to 20 nm. We used extreme ultraviolet interference lithography (EUV-IL) and a mechanical press to fabricate two-dimensional arrays of Au nanoparticles. Lithographically produced particle arrays were modified by hot pressing in a nanoimprint machine and the gap was varied in a range from 50 nm to below 20 nm. Optical measurement shows two resonances at 520 nm and 620 nm, with the latter gaining strength as the gap is reduced. The experimental and theoretical investigations using a FDTD algorithm demonstrate that the low-energy resonance can be assigned to a collective surface plasmon resonance arising from the strong near-field coupling between the nanoparticles. Surface Enhanced Raman Spectroscopy (SERS) experiments performed on a model molecule (BPE) show a large gain in signal intensity as a result of the reduced gaps between the particles.     

Polarization mapping of nanoparticle plasmonic coupling

We propose the use of polarization mapping as a tool to better separate the effects of plasmonic coupling from the local refractive index for molecular imaging and biosensing using gold nanoparticles. Polarization mapping allows identification of the orthogonal excitation mode when the particle dimer orientation is unknown, as may be the case when using plasmonic nanoparticles for cell labeling. This information can be used to sense relative changes in the dielectric environment, or for absolute dielectric sensing with additional a priori interparticle distance information. First, the theoretical scattering by nanoparticle pairs is modeled under parallel and orthogonal polarization orientations and increasing interparticle separation. Second, polarization mapping of substrate bound nanoparticles using dark-field microspectroscopy is investigated as a method to isolate the individual plasmonic coupling modes associated with a pair of nanoparticles without reorientation of the sample. The results of this study provide useful insight toward potential avenues for monitoring distances using plasmonic nanoparticles and sensing the local refractive index using nanoparticle pairs when the pair orientation is not known, as may be the case when using nanoparticles for cell receptor labeling.     

SERS active Ag nanoparticles in mesoporous silicon: detection of organic molecules and peptide–antibody assays

Ag nanoparticles synthesized on porous silicon samples were studied and applied as substrates for surface‐enhanced Raman scattering (SERS). The metallic nanostructures prepared by immersion plating were characterized by UV–Vis reflectance spectroscopy and scanning electron microscopy. SERS activity of the substrates was tested using Cyanine dye 1,3,3,1′,3′,3′‐esamethyl‐5,5′‐dimethoxyindodicarbocyanine iodide (Cy5‐OCH₃) as a probe molecule. The Raman spectra obtained for different excitation wavelengths indicate amplifications ascribed to plasmonic resonances with an enhancement factor up to 10⁷. CGIYRLRS peptides were chemisorbed on the Ag nanoparticles with the plasmonic resonance tuned at the excitation energy. Such oligopeptides were used as baits for a specific polyclonal antibody. The overall Raman enhancement allowed to evidence a good selectivity to the target analyte as required by most of the SERS applications on biological assays. Copyright © 2011 John Wiley & Sons, Ltd.     

Plasmonic nanoparticle monomers and dimers: from nanoantennas to chiral metamaterials

We review the basic physics behind light interaction with plasmonic nanoparticles. The theoretical foundations of light scattering on one metallic particle (a plasmonic monomer) and two interacting particles (a plasmonic dimer) are systematically investigated. Expressions for the effective particle susceptibility (polarizability) are derived, and applications of these results to plasmonic nanoantennas are outlined. In the long-wavelength limit, the effective macroscopic parameters of an array of plasmonic dimers are calculated. These parameters are attributable to an effective medium corresponding to a dilute arrangement of nanoparticles, i.e., a metamaterial where plasmonic monomers or dimers have the function of “meta-atoms”. It is shown that planar dimers consisting of rod-like particles generally possess elliptical dichroism and function as atoms for planar chiral metamaterials. The fabricational simplicity of the proposed rod-dimer geometry can be used in the design of more cost-effective chiral metamaterials in the optical domain.     

Magnetized spiral chains of plasmonic ellipsoids for one-way optical waveguides

When a linear chain of plasmonic nanoparticles is subject to longitudinal magnetic field, it exhibits optical Faraday rotation. If the magnetized nanoparticles are plasmonic ellipsoids arranged as a spiral chain, the interplay between the Faraday rotation and the geometrical spiral rotation (structural chirality) can strongly enhance nonreciprocity. This interplay forms a waveguide that permits one-way propagation only, within four disjoint frequency bands, two bands for each direction.     

Raman spectroscopic probing of plant material using SERS

We report surface‐enhanced Raman studies on intact plant material using onion layers as a biological target, and silver nanoaggregates and silver island films as enhancing plasmonic structures. Surface‐enhanced Raman scattering (SERS) enhancement allows the detection of strong Raman signatures of chemical constituents of the surface of the onion layer such as cellulose, proteins, and flavonols. Because of long‐time incubation, SERS sensors can access the extracellular space in the inner of the layer. The location of silver nanoparticles inside the onion layer has been monitored by the SERS images collected from chemicals present in the onion and/or reporter molecules attached to the nanoparticles. Our studies show a competitive adsorption of intrinsic bio molecules of the onion layer and reporter molecules. Different spectra from different places of the layer indicate the complex heterogeneous chemical structure of the plant material. The pH‐sensitive reporter molecule para mercapto benzoic acid attached to the nanoparticles allows us to infer pH values inside the extracellular matrix of the onion layer. Copyright © 2015 John Wiley & Sons, Ltd.     

A Sandwiched Biological Fluorescent Probe for the Diagnosis of Human Ovarian Tumor Based on TiO2 Nanoparticles

In this paper, we report a novel biological fluorescent probe for the diagnosis of human ovarian tumor based on sandwiched TiO₂ nanoparticles. The fluorescence nanoparticles consist of a fluorescent molecule, tetramethyl rhodamine isothiocyanate (TRITC), sandwiched between titanium dioxide (TiO₂) nanoparticles and nano-gold via reacting with each other. The antibodies HER2, labeled on the surface of the biofluorescence nanoparticles, have granted nanoparticles the privilege of aiming at peculiar tumor antigen. The specificity of antibody-nanoparticles interacting with cells was characterized by Laser Scanning Confocal Microscope. The results showed that these sandwiched nanoparticles were innocuous and stable, and the method offered potential advantages of sensitivity and simplicity due to high combing efficiency between nanoparticles and cells and provided an alternative method for the diagnosis of human ovarian tumor (HOT).     

2-氨基苯硫酚NIR-SERS光谱及其在纳米银表面吸附行为分析

本文采用静电自组装的方法制备了二维纳米银膜。UV-vis吸收光谱显示其等离子体共振吸收带位于400+900nm的光谱范围,延伸到了近红外区,可以较好的匹配785nm的近红外激发光源。以该纳米银膜为基底,对2-氨基苯硫酚(2-ATP)分子进行了近红外表面增强拉曼散射(NIR-SERS)检测,获得了重复性良好的NIR-SERS光谱图。实验表明:以2-ATP为探针分子时,该纳米银膜的NIR-SERS增强因子达到2.19×109。同时,本文采用密度泛函理论(DFT),以B3LYP/6-31G为基函数,对2-ATP分子进行结构优化和普通拉曼光谱(NR)计算,发现理论值和实验值吻合较好。此外,对2-ATP的NIR-SERS谱带进行了归属分析,发现当2-ATP分子在纳米银表面吸附时,是以-SH基团吸附到银表面,且同时-SH基团会被纳米银氧化。     

Binary teaching-learning-based optimization algorithm is used to investigate the superscattering plasmonic nanodisk

A new efficient binary optimization method based on Teaching-Learning-Based Optimization (TLBO) algorithm is proposed to design an array of plasmonic nanodisks in order to achieve maximum scattering coefficient spectrum. In binary TLBO (BTLBO), a group of learner consists of a matrix with binary entries; control the presence (‘1’) or the absence (‘0’) of nanodisks in the array. Simulation results show that scattering coefficient strongly depends on the localized position of nanoparticles and non-periodic structures have more appropriate response in term of scattering coefficient. This approach can be useful in optical applications such as plasmonic nanoantennas.     

Optical properties and biomedical applications of plasmonic nanoparticles

Nanoparticle plasmonics is a rapidly emerging research field that deals with the fabrication and optical characterization of noble metal nanoparticles of various size, shape, structure, and tunable plasmon resonances over VIS-NIR spectral band. The recent simultaneous advances in synthesis, characterization, electromagnetic simulation, and surface functionalization of plasmonic nanoparticles by biospecific molecular probes have led to a perfect publication storm in discoveries and potential biomedical applications of plasmon-resonant nanoparticle bioconjugates. Here, we present an overview of these topics. First, we discus basic wet-chemical routes to fabricate conjugates of gold, silver, or composite particles with controllable size, shape, structure and with surface functionalization by biospecific molecules. Second, we consider the single-particle dipole and multipole optics and coupled plasmonic nanoparticle arrays. Finally, we discus application of plasmonic bioconjugates to such fields as homogeneous and solid-phase assays, biomedical sensing and imaging, biodistribution and toxicity aspects, drug delivery and plasmonic photothermal therapy.     

Fluorescence characteristics of a molecule in the vicinity of a plasmonic nanomatryoska: Nonlocal optical effects

The fluorescence characteristics of a dipole molecule in the vicinity of a spherical multilayered metallic nanoshell (a plasmonic nanomatryoska) of ultra-small dimensions is studied via electrodynamic modeling, where we have computed the fluorescence decay rates, the shifts in emission frequency, and the overall fluorescence yields for molecular dipoles of both tangential and radial orientations. Our focus is on structures of ultra small dimensions in order to elucidate the possibly novel nonlocal optical effects in such a phenomenon. The results show that at very close distances between the molecule and the nanoshell, the nonlocal effects in general lead to smaller structure-induced effects with broadened and blue-shifted plasmonic resonances. These effects include overall smaller induced decay rates, smaller red-shifts in emission frequency, and somewhat larger fluorescence yields at low emission frequencies. Physical interpretation of our simulation results is provided.