Chiral Gold Nanorods with Five-Fold Rotational Symmetry and Orientation-Dependent Chiroptical Properties of Their Monomers and Dimers

Chiral plasmonic nanoparticles have attracted much attention because of their strong chiroptical responses and broad scientific applications. However, the types of chiral plasmonic nanoparticles have remained limited. Herein we report on a new type of chiral nanoparticle, chiral Au nanorod (NR) with five-fold rotational symmetry, which is synthesized using chiral molecules. Three different types of Au seeds (Au elongated nanodecahedrons, nanodecahedrons, and nanobipyramids) are used to study the growth behaviors. Different synthesis parameters, including the chiral molecules, surfactant, reductant, seeds, and Au precursor, are systematically varied to optimize the chiroptical responses of the chiral Au NRs. The chiral scattering measurements on the individual chiral Au NRs and their dimers are performed. Intriguingly, the chiroptical signals of the individual chiral Au NRs and their end-to-end dimers are similar, while those of the side-by-side dimers are largely reduced. Theoretical calculations and numerical simulations reveal that the different chiroptical responses of the chiral NR dimers are originated from the coupling effect between the plasmon resonance modes. Our study enriches chiral plasmonic nanoparticles and provides valuable insight for the design of plasmonic nanostructures with desired chiroptical properties.     

Thermal annealing of Au nanorod self-assembled nanostructured materials: morphology and optical properties

Three-dimensional Au nanorod and Au nanoparticle nanostructured materials were prepared by layer-by-layer self-assembly. The plasmonic properties of the Au nanorod and Au nanoparticle self-assembled nanostructured materials (abbreviated as AuNR and AuNP SANMs) are tunable by the controlled self-assembly process. The effect of thermal annealing at 180 and 500 degrees C to the morphologies, plasmonic properties and surface-enhanced Raman scattering (SERS) responses of these SANMs were investigated. According to the experimental results, these properties correlate with the structure of the SANMs.     

Sub-1.5 nm-gapped heterodimeric plasmonic nanomolecules

Plasmonic molecules are discrete assemblies of similar/dissimilar nanomaterials (atomic equivalents) with efficient inter-unit coupling toward electromagnetic hybridization. Albeit fundamentally and technologically very important, these structures are rare due to the lack of a general way to manipulate the structure, composition, and coupling of the nanoassemblies. While DNA nanotechnology offers a precious chance to build such structures, the weak coupling of DNA-bonded materials and the very limited material building blocks are two obstacles. This work aims to remove the bottlenecking barriers on the road to dimeric (and possibly more complicated) plasmonic molecules. After solving key synthetic issues, DNA-guided, solvo-driven Ag ion soldering is utilized to build a whole set (10 combinations of 4 metals) of homo/heterodimeric plasmonic nanomolecules with prescribed compositions. Importantly, strong in-solution electric-dipole coupling mediated by a sub-1.5 nm interparticle dielectric gap is achieved for materials with strong (Au, Ag) or damped (Pt, Pd) plasmonic responses. The involvement of Pt/Pd materials is of great value for plasmon-mediated catalysis. The broken dimeric symmetry is desirable for Fano-like resonance and photonic nanodiode devices, as well as lightening-up of plasmon dark states. The generality and reliability of the method would allow excitonic, nonlinear-optical, and magnetic units to be involved toward correspondingly enhanced functions.

A whole set of plasmonic nanodimers with prescribed binary compositions are constructed in solution to enable symmetry-broken strong plasmonic coupling.     

Catalytic DNA Origami-based Chiral Plasmonic Biosensor

Plasmonic circular dichroism(CD) has been emerged as a pro-mising signal for building biosensors due to its high sensitivity and specificity. In the past years, DNA nanotechnology enabled diverse chiral plasmonic devices, which can response biomolecules and then generate dynamic plasmonic CD signals at the visible range. Although some of them have been successfully employed as biosensors, the detection sensitivity is still relatively low. Herein we report a chiral plasmonic sensor with an improved detection sensitivity by integrating catalytic hairpin assembly circuits into DNA origami structures. We tested two kinds of tumor marker RNA sequences as detection targets and it turns out that the detection limit is below 10 pmol/L, improving one order of magnitude compared to previous work. The chiral plasmonic sensor with internal signal amplification circuits can stimulate a variety of smart nano-sensors for biological detection and offer a promising strategy for pathogenic RNA detection with plasmonic CD output.     

Controllable Preparation of Plasmonic Gold Nanostars for Enhanced Photothermal and SERS Effects

Gold nanostars(Au NSs) are asymmetric anisotropic nanomaterials with sharp edge structure. As a promising branched nanomaterial, Au NS has excellent plasmonic absorption and scattering properties. In order to tune the plasmonic photothermal and surface-enhanced Raman scattering(SERS) activity of Au NSs to obtain the desired characteristics, the effects of reagents on the local surface plasmon resonance(LSPR) bands of Au NSs were studied and the morphology and size were regulated. Nanoparticles with different sharp edges were synthesized to make their local plasmon resonance mode tunable in the visible and near-infrared region. The effects of the number and sharpness of different tips under the control of AgNO₃ on the photothermal response of Au NSs and the SERS activity and their mechanism were discussed in detail. The results show that as the length of the branch tip becomes longer and the sharpness increases, the plasmonic photothermal effect of Au NSs is strengthened, and the photothermal conversion efficiency is the highest up to 40% when the length of Au NSs is the longest. Au NSs with high SERS activity are used for the Raman detection substrate. Based on this property, the quantitative detection of the pesticide thiram is achieved.     

Designer Gold-Framed Palladium Nanocubes for Plasmon-Enhanced Electrocatalytic Oxidation of Ethanol

Surface plasmon of coinage metal nanostructures has been employed as a powerful route in boosting the performances in heterogenous catalysis. Development of efficient plasmonic nanocatalysts with high catalytic performance and efficient light harvesting properties is of vital importance. Herein, we rationally designed and synthesized a plasmonic nanocatalyst composed of Au-framed Pd nanocubes by an Ag(I)-assisted seed-mediated growth method. In the synthesis, the incorporation of Ag(I) suppresses the reduction of Au on the {100} surface of cubic Pd seeds and leads to the formation of Au nanoframes on the Pd nanocubes. The unique Au-framed Pd nanocubes can integrate the superior electrocatalytic of Pd and the outstanding plasmonic properties of Au. Thus, these nanostructures were employed as plasmonic nanocatalysts for plasmon-enhanced electrocatalytic oxidation of ethanol with improved stability.     

Plasmonic/Nonlinear Optical Material Core/Shell Nanorods as Nanoscale Plasmon Modulators and Optical Voltage Sensors

Herein, we report the design and synthesis of plasmonic/non‐linear optical (NLO) material core/shell nanostructures that can allow dynamic manipulation of light signals using an external electrical field and enable a new generation of nanoscale optical voltage sensors. We show that gold nanorods (Au NRs) can be synthesized with tunable plasmonic properties and function as the nucleation seeds for continued growth of a shell of NLO materials (such as polyaniline, PANI) with variable thickness. The formation of a PANI nanoshell allows dynamic modulation of the dielectric environment of the plasmonic Au NRs, and therefore the plasmonic resonance characteristics, by an external electrical field. The finite element simulation confirms that such modulation is originated from the field‐induced modulation of the dielectric constant of the NLO shell. This approach is general, and the coating of the Au NRs with other NLO materials (such as barium titanate, BTO) is found to produce a similar effect. These findings can not only open a new pathway to active modulation of plasmonic resonance at the sub‐wavelength scale but also enable the creation of a new generation of nanoscale optical voltage sensors (NOVS).     

Fine‐Tuning the Homometallic Interface of Au‐on‐Au Nanorods and Their Photothermal Therapy in the NIR‐II Window

The localized surface plasmon resonance (LSPR) of plasmonic nanomaterials is highly dependent on their structures. Going beyond simple shape and size, further structural diversification demands the growth of non‐wetting domains. Now, two new dimensions of synthetic controls in Au‐on‐Au homometallic nanohybrids are presented: the number of the Au islands and the emerging shapes. By controlling the interfacial energy and growth kinetics, a series of Au‐on‐AuNR hybrid structures are successfully obtained, with the newly grown Au domains being sphere and branched wire (nanocoral). The structural variety allowed the LSPR to be fine‐tuned in full spectrum range, making them excellent candidates for plasmonic applications. The nanocorals exhibit black‐body absorption and outstanding photothermal conversion capability in NIR‐II window. In vitro and in vivo experiments verified them as excellent photothermal therapy and photoacoustic imaging agents.     

均一取向等离子体二聚体的制备及光学机理

以单层SiO₂胶体微球为模板, 利用Au/SiO₂/Au交替沉积结合后退火处理的方法, 制备了一种垂直堆叠且均一取向的等离子体二聚体结构. 该方法具有很大的自由度, 可以通过调节实验流程来制备大面积取向相同的同质或异质纳米粒子二聚体. 所制备的纳米粒子的等离子体杂化效应明显, 在消光光谱中可以观察到成键及反键共振峰. 由于所得纳米粒子二聚体具有垂直堆叠的特殊规整取向, 还可以观察到所得样品等离子体吸收峰的角度依赖特性. 此外, 还探讨了Au/SiO₂/Au同质二聚体和Au/SiO₂/Ag异质二聚体的光学特性差异, 发现与Au/SiO₂/Au同质二聚体相比, Au/SiO₂/Ag异质二聚体由于Ag偶极等离子体模式与Au带间吸收的耦合而呈现Fano共振峰. 所得结果提供了一个调节贵金属等离子体光学共振峰位、 强度和波形的策略, 在纳米光子学领域有着广阔的应用前景, 对今后的实验和理论研究具有重要参考价值.     

Dodecahedral Au/Pt Nanobowls as Robust Plasmonic Electrocatalysts for Methanol Oxidation under Visible-Light Illumination

Plasmonic nanostructures with large absorption areas under resonant excitation have been utilized extensively in photon-assisted applications. In this work, dodecahedral Au nanobowls were first prepared by an easy and template-free method only through the introduction of H₂PtCl₆ and I⁻ during the growth procedure. The Au nanobowls show electron-field enhancement due to the high curvature of the bowl edge, the open region, and dodecahedral morphology. Au/Pt nanobowls, which couple plasmonic Au and catalytic Pt, were then constructed as plasmonic electrocatalysts for methanol oxidation. The mass activity reached 497.6 mA mg⁻¹ under visible-light illumination, which is 1.9 times that measured in the dark. Simultaneously, the electrocatalytic stability is also greatly improved under light excitation. The enhanced properties of the plasmonic Au/Pt electrocatalysts are ascribed to the synergistic effect of the plasmon-enhanced photothermal and hot-carrier effects on the basis of experimental investigations. This work thus offers an effective methodology to construct efficient plasmonic electrocatalysts for fuel cells.     

基于等离激元热电子调控的全谱光催化产氢增强（英文）

等离激元效应在光催化体系中的集成为实现广谱光吸收提供了一个新的途径,然而等离激元热电子的较低迁移率和不确定扩散方向使得其光催化效率仍较低.等离激元金属与n型半导体接触后,其界面间会形成肖特基结.在特定波长太阳光照射下,等离激元金属将其表面等离子体能量聚集在表面自由电子上,进而产生热电子.当这些热电子具有的能量高于肖特基势垒时,热电子便可注入到半导体导带上.与此同时,半导体上的电子可以通过肖特基接触发生回流,与金属上的空穴复合,进而降低半导体-等离激元金属复合材料的光催化性能.因此,为了提高光催化效率,如何调控等离激元热电子迁移和充分利用等离激元效应是一个重要挑战.本文尝试将"表面异质结"与肖特基结相结合的复合结构,得以有效地调控等离激元热电子的迁移.在该复合结构中,金纳米颗粒和铂纳米颗粒分别作为等离激元吸光单元和助催化剂,集成在TiO_2纳米片表面.其中"表面异质结"是由TiO_2纳米片的两种不同表面晶面所构成,我们选择由{001}和{101}两组晶面组成的TiO_2纳米片作为半导体衬底.该结构中的{001}晶面导带能级高于{101}导带能级,因而电子由高能级的{001}流向低能级的{101}晶面,可以用来引导等离激元热电子从可见光响应的金纳米颗粒向TiO_2进行高效转移.通过巯基丙酸的桥联作用,将等离激元Au纳米颗粒锚定在TiO_2纳米片的{001}晶面上,获得Au-TiO_2{001}样品.另一方面,利用TiO_2纳米片自身光生电荷导向性光沉积,得到与{101}晶面结合形成的Au-TiO_2{101}样品.我们对两组样品进行光电流和光催化产氢实验对比,确认在"表面异质结"诱导下Au-TiO_2{001}样品中Au产生的光生热电子可以更好地注入到TiO_2纳米片导带上.我们进一步通过光沉积Pt纳米颗粒来判定光生电子所能到达的区域,验证了以上结论.与此同时,肖特基结由铂纳米颗粒与TiO_2纳米片所形成,可以促使电子由TiO_2向铂纳米颗粒进行转移,而避免发生向金纳米颗粒的反向迁移,从而在Au-TiO_2体系中实现高效的单向载流子转移.基于该设计,等离激元光催化剂实现了明显改善的全谱光催化产氢性能.本文为全谱光催化的复合结构理性设计提供了一个新的思路.     

Plasmonic approach to enhanced fluorescence for applications in biotechnology and the life sciences

One of the most rapidly growing areas of physics and nanotechnology is concerned with plasmonic effects on the nanometer scale; these have applications in sensing and imaging technologies. Nanoplasmonic colloids such as Ag and Au have been attracting active interest, and there has been a recent explosion in the use of these metallic nanostructures to modify the spectral properties of fluorophores favorably and to enhance the fluorescence emission intensity. In this feature article, we summarize our work over a range of nanoplasmonics-assisted biological applications such as flow cytometry, immunoassays, cell imaging and bioassays where we use custom-designed plasmonic nanostructures (Ag and Au) to enhance fluorescence signatures. This fluorophore-metal effect offers unique advantages in providing improved photostability and enhanced fluorescence signals. We discuss the plasmonic enhancement of lanthanide fluorophores whose long and microsecond lifetimes offer the advantage of background-free fluorescence detection, but low photon cycling rates lead to poor brightness. We also show that plasmonic colloids are capable of enhancing the emission of fluorescent nanoparticles, including upconverting nanocrystals and lanthanide nanocomposites.     

Peapod‐Type Nanocomposites through the In Situ Growth of Gold Nanoparticles within Preformed Hexaniobate Nanoscrolls

A facile in situ method to grow Au nanoparticles (NPs) in hexaniobate nanoscrolls is applied to the formation of plasmonic Au@hexaniobate and bifunctional plasmonic‐magnetic Au‐Fe₃O₄@hexaniobate nanopeapods (NPPs). Utilizing a solvothermal treatment, rigid multiwalled hexaniobate nanoscrolls and partially filled Fe₃O₄@hexaniobate NPPs were first fabricated. These nanostructures were then used as templates for the controlled in situ growth of Au NPs. The resulting peapod structures exhibited high filling fractions and long‐range uniformity. Optical measurements showed a progressive red shift in plasmonic behavior between Au NPs, Au NPPs, and Au‐Fe₃O₄ NPPs; magnetic studies found that the addition of gold in the Fe₃O₄@hexaniobate NPPs reduced interparticle coupling effects. The development of this approach allows for the routine bulk preparation of noble‐metal‐containing bifunctional nanopeapod materials.     

In Situ Observation of Hot Carrier Transfer at Plasmonic Au/Metal-Organic Frameworks (MOFs) Interfaces

Constructing heterostructures have been demonstrated as an ideal strategy for boosting charge separation on plasmonic photocatalysts, but the detailed interface charge transfer mechanism remains elusive. Herein, that authors fabricate plasmonic Au and metal-organic frameworks (MOFs, NH₂−MIL-125 and MIL-125 used in this work) heterostructures and explore the interface charge transfer mechanism by in situ electron paramagnetic resonance (EPR) spectroscopy and electrochemical measurements. The plasmon-excited hot electrons on Au can transfer across the Au/MOF interface and be captured by the coordinatively unsaturated sites of secondary building units (Ti₈O₈(OH)₄ cluster) of the MOF structure, and the plasmon-excited hot holes on Au tend to transfer to and be trapped at the functionalized organic ligand (1,4-benzenedicarboxylate−NH₂). The spatially separated hot electrons and holes exhibit boosted the photocatalytic activity for chromium (VI) reduction and selective benzyl alcohol oxidation. This work illustrates the advantage of the versatile functionalization of MOF structures enabling molecular-level manipulation of interface charge transfer on plasmonic photocatalysts.     

Calixarene-encapsulated nanoparticles: self-assembly into functional nanomaterials

Calixarenes are excellent surfactants for enhancing the dispersion and self-assembly of metal nanoparticles into well-defined structures, particularly those with unit length scales in the 10-100 nm size range. Particles within these ensembles are strongly coupled, giving rise to unique collective optical or magnetic properties. The self-assembled nanostructures described in this feature article include 2D arrays of colloidal Au nanoparticles with size-dependent plasmonic responses, and sub-100 nm Co nanoparticle rings with chiral magnetic states. These nanoparticle assemblies may be further developed for applications in chemical sensing based on surface-enhanced Raman scattering (SERS) and as binary elements for nonvolatile memory, respectively.     

Gold nanobipyramid-embedded ultrathin metal nanoframes for in situ monitoring catalytic reactions

Metal nanoframes, especially ultrathin ones, with excellent plasmonic properties are synthetically interesting and highly attractive. Herein we report on the synthesis of Au nanobipyramid-embedded ultrathin metal nanoframes with one of the plasmon modes very similar to that of the Au nanobipyramids. The synthesis is mediated by silver coating on Au nanobipyramids. The excellent plasmonic properties of the Au nanobipyramid-embedded ultrathin metal nanoframes are ascribed to the little influence of the ultrathin metal nanoframes on the Au nanobipyramids, as verified by electrodynamic simulations. The increase in the amount of the added metal atoms changes the nanostructure from the nanoframe to a nanocage shape. The method has also been successfully applied to (Au nanobipyramid)@Ag nanorods with different lengths and Au nanobipyramids with different longitudinal dipolar plasmon wavelengths, suggesting the generality of our approach. We have further shown that the Au nanobipyramid-embedded ultrathin metal nanoframes possess an excellent surface-enhanced Raman scattering and outstanding in situ reaction probing performance. Our study opens up a route for the construction of plasmonic ultrathin metal nanoframes based on Au nanobipyramids for plasmon-enabled applications.

Ultrathin gold, palladium and platinum nanoframes are synthesized for monitoring reactions. Each nanoframe contains a gold nanobipyramid at its center.     

Multiple plasmonic effect on photocurrent generation of metal‐loaded titanium dioxide composite/dye films on gold grating surface

We demonstrate the multiple plasmonic effect on the photocurrent properties of photoanodes containing Ag or Au nanoparticles (NPs) loaded onto titanium dioxide film (Ag–TiO₂ or Au–TiO₂) on Au grating surfaces. Ag–TiO₂ or Au–TiO₂ nanocomposite particles are prepared by a flame spray pyrolysis route. The structures and morphologies of the prepared products are characterized by high‐resolution transmission electron microscopy. The Ag–TiO₂ or Au–TiO₂ composite NPs are deposited by spin coating onto the Au grating surfaces. The photoanode electrode is a layered structure of blu‐ray disc‐recordable grating substrate/Au/Ag (or Au)–TiO₂/dye/electrolyte/indium‐tin oxide. The plasmonic effect is induced when Ag or Au NPs are located within the propagating surface plasmon (SP) field on the Au grating surface. The short‐circuit photocurrent is increased by exciting the grating‐coupled propagating SP on the Au gratings and is further enhanced by positioning the Ag or Au NPs within the grating‐coupled SP field. Copyright © 2014 John Wiley & Sons, Ltd.     

Atomically precise Au25(GSH)18 nanoclusters versus plasmonic Au nanocrystals: Evaluating charge impetus in solar water oxidation

Atomically precise metal nanoclusters (NCs) have been deemed as an emerging class of metal nanomaterials owing to fascinating size-dependent physicochemical properties, discrete energy band structure, and quantum confinement effect, which are distinct from conventional metal nanoparticles (NPs). Nevertheless, metal NCs suffer from photoinduced self-oxidative aggregation accompanied by in-situ transformation to metal NPs, markedly reducing the photosensitization of metal NCs. Herein, maneuvering the generic instability of metal NCs, we perform the charge transport impetus comparison between atomically precise metal NCs and plasmonic metal NPs counterpart obtained from in-situ self-transformation of metal NCs in photoelectrochemical (PEC) water splitting reaction. For conceptual demonstration, we proposed two quintessential heterostructures, which include TNTAs-Au₂₅ heterostructure fabricated by electrostatically depositing glutathione (GSH)-protected Au₂₅(GSH)₁₈ NCs on the TiO₂ nanotube arrays (TNTAs) substrate, and TNTAs-Au heterostructure constructed by triggering self-transformation of Au₂₅(GSH)₁₈ NCs to plasmonic Au NPs in TNTAs-Au₂₅ via calcination. The results indicate that photoelectrons produced over Au₂₅ NCs are superior to hot electrons of plasmonic Au NPs in stimulating the interracial charge transport toward solar water oxidation. This is mainly ascribed to the significantly accelerated carrier transport kinetics, prolonged carrier lifespan, and substantial photosensitization effect of Au₂₅ NCs compared with plasmonic Au NPs, resulting in the considerably enhanced PEC water splitting performance of TNTAs-Au₂₅ relative to plasmonic TNTAs-Au counterpart under visible light irradiation. Our work would provide important implications for rationally designing atomically precise metal NCs-based photosystems toward solar energy conversion.     

Fine-Tuning the Homometallic Interface of Au-on-Au Nanorods and Their Photothermal Therapy in the NIR-II Window

The localized surface plasmon resonance (LSPR) of plasmonic nanomaterials is highly dependent on their structures. Going beyond simple shape and size, further structural diversification demands the growth of non-wetting domains. Now, two new dimensions of synthetic controls in Au-on-Au homometallic nanohybrids are presented: the number of the Au islands and the emerging shapes. By controlling the interfacial energy and growth kinetics, a series of Au-on-AuNR hybrid structures are successfully obtained, with the newly grown Au domains being sphere and branched wire (nanocoral). The structural variety allowed the LSPR to be fine-tuned in full spectrum range, making them excellent candidates for plasmonic applications. The nanocorals exhibit black-body absorption and outstanding photothermal conversion capability in NIR-II window. In vitro and in vivo experiments verified them as excellent photothermal therapy and photoacoustic imaging agents.     

金纳米颗粒在等离子体共振光催化剂中的作用机理研究

金纳米颗粒在等离子体共振光催化剂中具有多种不同的作用机理。本文采用溶胶-凝胶法合成了氮/碳共掺杂超薄二氧化钛(D-TiO₂)包覆的SiO₂/Au/D-TiO₂三明治型及SiO₂/D-TiO₂核壳纳米结构材料,对金纳米颗粒在含有可见光响应型半导体的等离子体共振光催化剂光催化分解水制氢反应中的作用机理进行了探索。研究结果表明,在该等离子体共振光催化剂的光催化反应过程中,金纳米颗粒同时体现出肖特基效应和等离子体共振效应作用机理,且作用机理与光生载流子的多少以及金纳米颗粒的负载量有关。负载量较低时,金纳米颗粒的作用机理与光生载流子的多少有关。而在高负载量条件下,金纳米颗粒在可见光照射下主要表现出肖特基效应对光催化活性的影响。