Environmental Optical Sensitivity of Gold Nanodecahedra

The sensitivity of localized surface plasmon resonances with respect to changes in the refractive index of the surrounding medium is measured for small (< 60 nm side length) and large (ca. 150 nm side length) regular gold nanodecahedra (pentagonal bipyramids), and compared to rigorous solutions of Maxwell's equations for bicones based upon the boundary element method (BEM). Small particles are prepared through ultrasound‐induced reduction of HAuCl₄ by N,N‐dimethylformamide (DMF) on presynthesized penta‐twinned Au seeds, whereas large decahedra are grown using smaller ones as seeds. Excellent agreement between experimental and calculated spectra is found for dispersions and monolayers of particles in different solvents, as well as for the effect of uniform silica layers of various thicknesses grown on them. These results are expected to be useful for the development of novel biosensors.     

Investigation on refractive index sensing of single silver nanoparticle at tightly focused light illumination

Based on the generalized Mie theory, refractive index sensing characteristics of single silver nanoparticle respectively illuminated by tightly focused linearly-polarized and radially-polarized light beams are investigated. The spectra for localized surface plasmon resonances (LSPR) under different dielectric environments demonstrate that distinct dipolar and quadrupolar resonances can be always observed for the case of radial polarization, while there is only strong dipolar resonance for the case of linear polarization. The dipolar mode has a higher sensitivity. However, the figure of merit (FOM) for the quadrupolar resonance is much higher than that for the dipolar resonance, because the quadrupolar resonance has a narrower width.     

长径比对金纳米棒折射率传感灵敏度的影响

利用化学种子生长法制备了多种长径比的金纳米棒,通过监测不同折射率下金纳米棒的局域表面等离子体共振(LSPR)波长移动来研究其折射率传感的灵敏度。实验结果表明,随着纳米棒长径比增加,其折射率传感的灵敏度近似线性地提高。在监测波长范围内,灵敏度从长径比为2.5：1时的216nm/RIU增长至4.2：1时的352nm/RIU。对于长径比为4.2:1的金纳米棒,用离散偶极子近似(DDA)的方法模拟了其折射率传感的灵敏度,与实验结果基本一致。     

修饰不同金纳米颗粒的极大角倾斜光纤光栅折射率传感特性研究

研究了分别使用大尺寸金纳米壳与星型金纳米颗粒修饰极大角倾斜光纤光栅(ExTFG)的局域表面等离子体共振(LSPR)传感器,实验对比了这两种ExTFG-LSPR传感器的折射率传感特性。实验结果表明:修饰星型金纳米颗粒的ExTFG传感器,其TM、TE模的基于波长变化的折射率灵敏度分别提升约15.52和12.8nm/RIU,但共振吸收效应不明显;而修饰大尺寸金纳米壳的ExTFG传感器,在大尺寸金纳米壳的LSPR作用下,其TM、TE模的基于波长变化的折射率灵敏度分别提升约31.1和26.99nm/RIU,同时,TM与TE模在C-L波段表现出强烈的共振吸收,基于归一化强度变化的折射率灵敏度分别约为185.18%/RIU和251.83%/RIU。     

银纳米颗粒的局域表面等离子体共振传感

采用微波法合成银纳米颗粒,通过化学自组装技术将银纳米颗粒吸附在玻璃基片上,制备了银纳米颗粒的局域表面等离子体传感器。在纯水中,紫外可见光消光谱表明局域表面等离子体共振位于428nm处。随外界折射率增加,共振峰发生红移,其折射率灵敏度达到173±6nm/RIU。在350oC温度下退火处理后,改变银颗粒在基片上的形貌,峰位发生约65nm的红移,灵敏度下降约20%。理论分析表明,银纳米颗粒形状和基底的相互作用影响折射率传感的波长响应和灵敏度特性。     

Penta‐Twinned Copper Nanorods: Facile Synthesis via Seed‐Mediated Growth and Their Tunable Plasmonic Properties

The use of seed‐mediated growth as a versatile approach to the synthesis of penta‐twinned Cu nanorods with uniform diameters and controllable aspect ratios is reported. The success of this approach relies on our recent synthesis of uniform Pd decahedra, with sizes in the range of 6–20 nm. The Pd decahedral seeds can direct the heterogeneous nucleation and growth of Cu along the fivefold axis to produce nanorods with uniform diameters defined by the lateral dimension of the original seeds. Due to a large mismatch in the lattice constants between Cu and Pd (7.1%), the deposited Cu is forced to grow along one side of the Pd decahedral seed, generating a nanorod with an asymmetric distribution of Cu, with the Pd seed situated at one of the two ends. According to extinction spectra, the as‐obtained Cu nanorods can be stored in water under the ambient conditions for at least six months without noticeable degradation. This excellent stability allows us to systematically investigate the size‐dependent surface plasmon resonance properties of the penta‐twinned Cu nanorods. With the nanorod transverse modes positioned at 560 nm, the longitudinal modes can be readily tuned from the visible to the near‐infrared region by controlling the aspect ratio.     

基于表面等离子体共振的光子晶体光纤折射率传感器的设计与分析

为了实现光子晶体光纤在近红外波段下的高灵敏度传感,设计了一种基于表面等离子体共振的光子晶体光纤(SPR-PCF)折射率型传感器。光纤内部的空气孔呈六边形排列,金纳米层完全包覆光纤外璧并与圆形待测物通道接触。利用有限元矢量软件COMSOL对SPR-PCF传感器的光学特性进行数值模拟仿真,得到不同待测物折射率的共振波长并绘制出纤芯损耗光谱,通过纤芯损耗光谱来对SPR-PCF传感器的传感特性进行分析。实验结果表明,其折射率测量区间为1.31~1.38,最大光谱灵敏度为104 nm/RIU,最大振幅灵敏度为200RIU-1,折射率测量精度为2.94×10-5RIU。     

基于倾斜光纤光栅及其表面等离子效应的折射率传感比较研究(英文)

介绍了倾斜光纤光栅作为折射率传感器的测量原理,给出它的倾斜角8°与中心波长1550nm的反射谱与透射谱,分析了具有表面等离子的倾斜光纤光栅传感机理。为验证折射率传感的可能性与优点,进行了蔗糖浓度溶液的裸倾斜光纤光栅与镀金的倾斜光纤光栅的折射率测量分析,证明镀金后的表面等离子效应倾斜光纤光栅折射率传感器其灵敏度大大增加。     

A localized surface plasmon resonance DNA biosensor based on gold nanospheres coated on the tip of the fiber

A localized surface plasmon resonance (LSPR) biosensor was prepared with gold nanospheres (AuNSs) coated on the tip face of the optical silica fiber. AuNSs with the sizes of 20 nm and 80 nm were used. The sensitivities of AuNS20 nm and AuNS80 nm modified sensors to bulk refractive index (RI) variation are 82.86 nm/RIU and 218.98 nm/RIU, respectively. The AuNS80 nm modified sensor was used for the detection of 40 bases DNA hybridization and the limit of detection is 50 nmol/L, where the 40-bases DNA probe was covalently linked with AuNS80 nm. The complementary DNA sequence in tris-acetate-EDTA (TAE) buffer solution was detected as the target DNA. This fiber sensor has the advantages of small sample consumption, easy fabrication and high sensitivity.     

基于氧化锡铟纳米薄膜的圆形晶格光子晶体光纤折射率传感器

为了实现近红外波段的高灵敏度传感,设计并研究了一种基于表面等离子体共振的光子晶体光纤(Surface Plasmon Resonance Photonic Crystal Fiber,SPR-PCF)折射率传感器.该光纤横截面的空气孔排列方式是圆形晶格,呈现出向 日葵形状.光纤包层的外壁淀积了氧化锡铟(Indium T...     

Optimizing the NIR Fluence Threshold for Nanobubble Generation by Controlled Synthesis of 10–40 nm Hollow Gold Nanoshells

The laser fluence to trigger nanobubbles around hollow gold nanoshells (HGN) with near infrared light is examined through systematic modification of HGN size, localized surface plasmon resonance (LSPR), HGN concentration, and surface coverage. Improved temperature control during silver template synthesis provides monodisperse, silver templates as small as 9 nm. 10 nm HGN with <2 nm shell thickness are prepared from these templates with a range of surface plasmon resonances from 600 to 900 nm. The fluence of picosecond near infrared (NIR) pulses to induce transient vapor nanobubbles decreases with HGN size at a fixed LSPR wavelength, unlike solid gold nanoparticles of similar dimensions that require an increased fluence with decreasing size. Nanobubble generation causes the HGN to melt with a blue shift of the LSPR. The nanobubble threshold fluence increases as the irradiation wavelength moves off the nanoshell LSPR. Surface treatment does not influence the threshold fluence. The threshold fluence increases with decreasing HGN concentration, suggesting that light localization through multiple scattering plays a role. The nanobubble threshold to rupture liposomes is four times smaller for 10 nm than for 40 nm HGN at a given LSPR, allowing us to use HGN size, LSPR, laser wavelength and fluence to control nanobubble generation.     

Double Fano resonances in disk-nonconcentric ring plasmonic nanostructures

The plasmonic properties of gold nanostructures composed of a disk outside a nonconcentric ring are numerically studied by the finite difference time domain(FDTD) method. Simulated results show that two Fano resonances are formed as a result of the coupling of the octupolar and quadrupolar modes of the ring with the dipolar mode of the disk. The reduction in structural symmetry causes a red shift of the Fano resonances and distinct changes in spectral lineshape by offsetting the center of the in...     

Solvent‐Mediated Plasmon Tuning in a Gold‐Nanoparticle–Poly(Ionic Liquid) Composite

The design, synthesis, and characterization of a hierarchically ordered composite whose structure and optical properties can be reversibly switched by adjustment of solvent conditions are described. Solvent‐induced swelling and de‐swelling is shown to provide control over the internal packing arrangement and hence, optical properties of in situ synthesized metal nanoparticles. Specifically, a gold‐nanoparticle‐containing ionic‐liquid‐derived polymer is synthesized in a single step by UV irradiation of a metal‐ion‐precursor‐doped, self‐assembled ionic liquid gel, 1‐decyl‐3‐vinylimidazolium chloride. Small‐angle X‐ray scattering (SAXS) studies indicate that in the de‐swollen state, the freestanding polymer adopts a perforated lamellar structure. Optical spectroscopy of the dried composite reveals plasmon resonances positioned in the near‐IR. Strong particle–particle interactions arise from matrix‐promoted formation of aggregated 1D clusters or chains of gold nanoparticles. Upon swelling in alcohol, the composite undergoes a structural conversion to a disordered structure, which is accompanied by a color change from purple to pale pink and a shift in the surface plasmon resonance to 527 nm, consistent with isolated, non‐interacting particles. These results demonstrate the far‐field tuning of the plasmonic spectrum of gold nanoparticles by solvent‐mediated changes in its encapsulating matrix, offering a straightforward, low‐cost strategy for the fabrication of nanophotonic materials.     

Au@pNIPAM Thermosensitive Nanostructures: Control over Shell Cross‐linking,Overall Dimensions,and Core Growth

Thermoresponsive nanocomposites comprising a gold nanoparticle core and a poly(N‐isopropylacrylamide) (pNIPAM) shell are synthesized by grafting the gold nanoparticle surface with polystyrene, which allows the coating of an inorganic core with an organic shell. Through careful control of the experimental conditions, the pNIPAM shell cross‐linking density can be varied, and in turn its porosity and stiffness, as well as shell thickness from a few to a few hundred nanometers is tuned. The characterization of these core–shell systems is carried out by photon‐correlation spectroscopy, transmission electron microscopy, and atomic force microscopy. Additionally, the porous pNIPAM shells are found to modulate the catalytic activity, which is demonstrated through the seeded growth of gold cores, either retaining the initial spherical shape or developing a branched morphology. The nanocomposites also present thermally modulated optical properties because of temperature‐induced local changes of the refractive index surrounding the gold cores.     

Supported Faceted Gold Nanoparticles with Tunable Surface Plasmon Resonance for NIR‐SERS

A novel dry plasma methodology for fabricating directly stabilized substrate‐supported gold nanoparticle (NP) ensembles for near infrared surface enhanced Raman scattering (NIR SERS) is presented. This maskless stepwise growth exploits Au‐sulfide seeds by plasma sulfidization of gold nuclei to produce highly faceted Au NPs with a multiple plasmon resonance that can be tuned from the visible to the near infrared, down to 1400 nm. The role of Au sulfidization in modifying the dynamics of Au NPs and of the corresponding plasmon resonance is discussed. The tunability of the plasmon resonance in a broad range is shown and the effectiveness as substrates for NIR SERS is demonstrated. The SERS response is investigated by using different laser sources operating both in the visible and in the NIR. SERS mapping of the SERS enhancement factor is carried out in order to evaluate their effectiveness, stability, and reproducibility as NIR SERS substrates, also in comparison with gold NPs fabricated by conventional sputtering and with the state‐of‐the‐art in the current literature.     

Tailoring the Plasmonic Modes of a Grating‐Nanocube Assembly to Achieve Broadband Absorption in the Visible Spectrum

Engineered metal‐dielectric‐metal nanostructures with broadband absorbing properties in the visible spectral range are fabricated by combining the plasmonic resonances of different noble metal nanostructures. Silver nanocubes and gold nanogratings couple to each other using a dielectric polymer spacer with controllable thickness, resulting in a large multiplicative enhancement of absorption properties across a broad spectral range. Narrow, long nanogrooves in a gold film are first fabricated using electron beam lithography, after which a polymer spacer layer with a controllable thickness ranging from 4 to 12 nm is assembled by spin‐assisted layer‐by‐layer assembly. Finally, silver nanocubes with different surface coverages ranging from 12% to 22% are deposited using the Langmuir–Blodgett technique. The individual plasmon resonances of these different nanostructures are located at significantly different optical frequencies and are tuned in this study to allow a significant increase of light absorbance of the original gratings to an average value of 84% across the broad wavelength range of 450–850 nm.     

Gold Coating of Silver Nanoprisms

Core–shell Ag@Au nanoprisms are prepared through a surfactant‐free seed‐mediated approach by taking advantage of the anisotropic structure of silver nanoprisms as seeds. The gold coating on the silver nanoprism surface is achieved by using hydroxylamine as a mild reducing agent, and the final fully gold‐coated prism structures are confirmed by microscopic and spectroscopic characterization. The resulting Ag@Au core–shell structure preserves the optical signatures of nanoprisms and offers versatile functionality and particularly better stability against oxidation than the bare silver nanoprism. The surface plasmon resonances of the core–shell Ag@Au nanoprisms can be tuned throughout the visible and near‐IR range as a function of the Au shell thickness. Such tailorable optical features and surfactant‐free gold shells have great potential applications in biosensing and bioimaging.     

Third‐Order Nonlinear Optical Response of Gold‐Island Films

Films of gold nanoscaled islands with thicknesses ranging between 0.5 and 15 nm were prepared by thermal evaporation onto untreated and aminosilane‐pretreated glass substrates. Post‐deposition annealing was found to modify the morphological characteristics of the islands (e.g., average island area and height, inter‐island distance, etc.), resulting in changes of the localized surface plasmon resonance (SPR) characteristics and, therefore, modifying the nonlinear optical (NLO) response of the films. The NLO response of both unannealed and annealed (20 h at 200 °C) films was studied by means of the optical Kerr effect (OKE), using 35 ps, 532 nm laser excitation, while measurements performed by means of the Z‐scan technique allowed for the determination of both the nonlinear refraction and absorption characteristics of the films. The results are discussed and compared with other reports.     

基于MSM结构的表面等离子体共振光纤折射率传感器

基于表面等离子体共振(SPR)效应,设计了一种基于多模-单模-多模(MSM)结构的光纤折射率传感器。采用光纤熔接的方式构成MSM结构,并且在单模光纤的表面涂覆二氧化钛/银(TiO2/Ag)复合膜构成传感单元。利用FDTD Solutions仿真分析了单模光纤长度与金属膜厚度对传感器性能的影响。结果表明:单模光纤长度越长,共振深度越深;TiO2/Ag复合膜中Ag膜厚度为50nm,TiO2膜厚度为20nm时,传感器性能最优,在1.33~1.41环境折射率范围内,传感器的灵敏度约为6 875nm/RIU。实验结果表明该光纤折射率传感器结构制作工艺简单、灵敏度高。     

Drug Delivery: Wavelength‐Selective Light‐Induced Release from Plasmon Resonant Liposomes (Adv. Funct. Mater. 6/2011)

Biodegradable, spectrally tunable plasmon resonant nanocapsules are created via the deposition of gold onto the surface of 100 nm diameter thermosensitive liposomes. These nanocapsules exhibit selective release of encapsulated contents upon illumination with light of a wavelength matching their distinct resonance bands. In this study, 760 and 1210 nm laser illumination elicits complete release from gold‐coated liposomes with a corresponding resonance, while causing minimal release from liposomes with an unmatching resonance. Spectrally selective release is accomplished through the use of multiple, low‐intensity laser pulses delivered over a period of minutes, ensuring that illumination affects the gold‐coated liposomes without heating the surrounding media. The use of pulsed illumination to achieve spectral selectivity is validated experimentally and through modeling of the heat equation. The result of this illumination scheme for selective release using multiple wavelengths of light is a biologically safe mechanism for realizing drug delivery, microfluidic, and sensor applications.