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).     

Plasmonics for pulsed-laser cell nanosurgery: Fundamentals and applications

This review describes the fundamental aspects of pulsed laser interaction with plasmonic nanostructures, and its applications to cell nanosurgery, including the destruction, modification or manipulation of molecular, sub-cellular and cellular structures. The review assumes no prior knowledge of the field of plasmonics and begins with a short review of the basic theory of plasmon excitation and optical properties of nanoscale metallic structures. Fundamentals of short and ultrashort laser pulse interaction with plasmonic nanostructures in a water environment are then discussed. Special emphasis is put on the consequences of the irradiation on the surrounding environment of the nanostructure, including heating, low-density plasma generation, pressure wave release and formation of vapor bubbles. The paper is concluded with a review of different applications of pulsed-laser interaction with plasmonic nanostructures for cell nanosurgery, including photothermal therapy, plasmonic enhanced cell transfection, molecular surgery and drug delivery.     

Room‐temperature Synthesis of Amorphous Molybdenum Oxide Nanodots with Tunable Localized Surface Plasmon Resonances

Two‐dimensional (2D) semiconductors have recently emerged as a remarkable class of plasmonic alternative to conventional noble metals. However, tuning of their plasmonic resonances towards different wavelengths in the visible‐light region with physical or chemical methods still remains challenging. In this work, we design a simple room‐temperature chemical reaction route to synthesize amorphous molybdenum oxide (MoO_3−x ) nanodots that exhibit strong localized surface plasmon resonances (LSPR) in the visible and near‐infrared region. Moreover, tunable plasmon resonances can be achieved in a wide range with the changing surrounding solvent, and accordingly the photoelectrocatalytic activity can be optimized with the varying LSPR peaks. This work boosts the light–matter interaction at the nanoscale and could enable photodetectors, sensors, and photovoltaic devices in the future.     

Coupling between molecular and plasmonic resonances in freestanding dye-gold nanorod hybrid nanostructures

Hybrid nanostructures of organic dyes and inorganic gold nanorods are constructed using the layer-by-layer assembly method via electrostatic interactions. Strong coupling is observed between the molecular resonance of dyes and the plasmonic resonance of gold nanorods when their spectra overlap strongly. The coupling strength is tuned by choosing gold nanorods with longitudinal plasmon wavelengths varying from 570 to 870 nm. The resonance coupling-induced plasmon shift is found to be strongly dependent on the dye concentration and the spacing between the dye and nanorod. Moreover, the resonance coupling can be switched off by laser illumination to decompose adsorbed dyes. We believe this is the first time that the coupling between molecular and plasmonic resonances is observed for freestanding hybrid nanostructures constructed out of dyes and colloidal gold nanorods. These results will be helpful in understanding the fundamental interactions between molecular and plasmonic resonances and useful for the design of resonance coupling-based chemical and biological sensors.     

One-dimensional nanostructures of metals: large-scale synthesis and some potential applications

We review recent developments in our group regarding the solution-phase synthesis of one-dimensional nanostructures of metals. The synthetic approaches include solution-liquid-solid growth for nanowires of low-melting-point metals such as Pb; seed-directed growth for Ag nanowires, nanobeams, and nanobelts; kinetically controlled growth for Pt nanorods, nanowires, and multipods; and galvanic replacement for nanotubes of Au, Pt, and Pd. Both characterization and mechanistic studies are presented for each nanostructure. Finally, we highlight the electrical and plasmonic properties of these metal nanostructures and discuss their potential applications in nanoscale devices.     

Sensing using localised surface plasmon resonance sensors

The bright colours of noble metal particles have attracted considerable interest since historical times, where they were used as decorative pigments in stained glass windows. More recently, the tuneable optical properties of metal nanoparticles and their addressability via spectroscopic techniques have brought them back into the forefront of fundamental and applied research fields. Much of the recent attention concerning metal nanoparticles such as gold and silver has been their use as small-volume, ultra-sensitive label-free optical sensors. Plasmonic nanoparticles act in this case as transducers that convert changes in the local refractive index into spectral shifts of the localized surface plasmon resonance (LSPR) band. This LSPR-shift assay is a general technique for measuring binding affinities and rates from any molecule that induces a change in the local refractive index around the metallic nanostructures. By attaching molecular recognition elements (chemical or biological ligands) on the nanostructures, specificity and selectivity to the analyte of interest are introduced into the nanosensor. In this review, we will discuss the different methods used to fabricate plasmonic nanosensors. A special emphasis will be given to techniques used to link plasmonic nanostructures to surfaces. While the difference between colorimetric and refractive index sensing approaches will be briefly described, the importance to distinguish between bulk refractive index (RI) sensing and molecular near-field refractive index sensing will be discussed. The recent progress made in the development of novel surface functionalization strategies together with the formation of optically and mechanically stable LSPR sensors will be highlighted.     

Plasmonic biosensing based on non-noble-metal materials

This review focuses on the research progress of non-noble-metal materials with nanostructures for plasmonic biosensing. Firstly, the physical and sensing principles of localized surface plasmon resonance (LSPR) sensors are briefly introduced; then non-noble-metal materials, such as copper, aluminum, semiconductor, graphene and other materials, for plasmonic sensing are categorized and presented. Finally, a rational discussion about the future prospective of novel materials for plasmonic sensing is given.     

Recent Advances in Plasmonic Nanostructures Applied for Label-free Single-cell Analysis

Cellular heterogeneity presents a major challenge in understanding the relationship between cells of particular genotype and response in disease. In order to characterize the cell-to-cell differences during the biochemical processes, single-cell analysis is necessary. Profiting from the unique localized surface plasmon resonance (LSPR) and Mie scattering, plasmonic nanostructures have revealed stable and adjustable scattering signals, avoiding photobleaching, blinking and autofluorescence phenomenon. These characterizations are propitious to the dynamic trace and biological image of single living cells. In this review, we discuss the recent advances in plasmonic nanostructures applied for label-free detection and monitoring of target cells at single-cell level by using three different techniques, surface-enhanced Raman scattering (SERS), surface-enhanced Infrared absorption spectroscopy (SEIRAS), and dark-field microscopy. Various avenues to design plasmonic probes combining spectra and imaging for single-cell analysis are demonstrated as well. We hope this review can highlight the superiority of plasmonic nanostructures in single cellular analysis, and further motivate the development of label-free cell analysis technique to elucidate cellular diversity and heterogeneity.     

Probing plasmonic nanostructures by photons and electrons

We discuss recent developments for studying plasmonic metal nanostructures. Exploiting photons and electrons opens up new capabilities to probe the complete plasmon spectrum including bright and dark modes and related local optical fields at subnanometer spatial resolution. This comprehensive characterization of plasmonic properties of metal nanostructures provides new basic insight into the fundamental physics of “surface enhanced” spectroscopy in hottest hot spots and enables us to optimize plasmon supported processes and devices.     

Recent developments and applications of hybrid surface plasmon resonance interfaces in optical sensing

Nanostructured noble metals exhibit an intense optical near field due to surface plasmon resonance, therefore promising widespread applications and being of interest to a broad spectrum of scientists, ranging from physicists, chemists, and materials scientists to biologists. A wealth of research is available discussing the synthesis, characterization, and application of noble metal nanoparticles in optical sensing. However, with respect to the sensitivity of the frequency and width of these surface plasmon resonance modes to the particle’s shape, size, and environment, in nearly every case, success strongly depends on the availability of highly stable, adhesive, and sensitive nanoparticles. This undoubtedly presents a challenging task to nanofabrication. The past decade has witnessed fascinating advances in this field, in particular, the construction of oxide-based hybrid plasmonic interfaces to overcome the problem addressed above by (1) coating the metallic nanostructures with thin overlayers to form sandwiched structures or (2) embedding metallic nanostructures in a dielectric matrix to obtain metal/dielectric matrix nanocomposite films. In this critical review, we focus on recent work related to this field, beginning with a presentation of hybrid films with enhanced structural and optical stability, readily and selectively designed using chemical and physical techniques. We then illustrate their interesting optical properties and demonstrate exciting evidence for the postulated application in surface plasmon sensing fields. Finally, we survey the work remaining to be done for that potential to be realized.     

Progress in electrochemistry of hybrid diamond/sp2-C nanostructures

Hybrid diamond/sp²-C nanostructures have aroused growing interests in electrochemistry currently owing to the good chemical/physical properties, including high electrical conductivity, mechanical robustness, and high specific surface area, as well as the unique electrochemical properties, namely, an enhanced electrochemical activity while retaining a wide potential window and low background currents when properly engineering the microstructure. This mini-review presents the recent electrochemistry process of diamond/sp²-C nanostructures. In particular, the synthetic methods, microstructures, and possible growth mechanism of diamond/sp²-C nanostructures are briefly summarized. Then, the electrochemical property tailoring is addressed in detail, and subsequently, their potential applications in electrochemistry including electrochemical sensors, supercapacitors, electrocatalysis, and other applications are discussed. The future perspectives of diamond/sp²-C nanostructures in electrochemistry finally conclude this review.     

Electrochemical Synthesis of Plasmonic Nanostructures

Thanks to their tunable and strong interaction with light, plasmonic nanostructures have been investigated for a wide range of applications. In most cases, controlling the electric field enhancement at the metal surface is crucial. This can be achieved by controlling the metal nanostructure size, shape, and location in three dimensions, which is synthetically challenging. Electrochemical methods can provide a reliable, simple, and cost-effective approach to nanostructure metals with a high degree of geometrical freedom. Herein, we review the use of electrochemistry to synthesize metal nanostructures in the context of plasmonics. Both template-free and templated electrochemical syntheses are presented, along with their strengths and limitations. While template-free techniques can be used for the mass production of low-cost but efficient plasmonic substrates, templated approaches offer an unprecedented synthetic control. Thus, a special emphasis is given to templated electrochemical lithographies, which can be used to synthesize complex metal architectures with defined dimensions and compositions in one, two and three dimensions. These techniques provide a spatial resolution down to the sub-10 nanometer range and are particularly successful at synthesizing well-defined metal nanoscale gaps that provide very large electric field enhancements, which are relevant for both fundamental and applied research in plasmonics.     

Faradaurate nanomolecules: a superstable plasmonic 76.3 kDa cluster

Information on the emergence of the characteristic plasmonic optical properties of nanoscale noble-metal particles has been limited, due in part to the problem of preparing homogeneous material for ensemble measurements. Here, we report the identification, isolation, and mass spectrometric and optical characterization of a 76.3 kDa thiolate-protected gold nanoparticle. This giant molecule is far larger than any metal-cluster compound, those with direct metal-to-metal bonding, previously known as homogeneous molecular substances, and is the first to exhibit clear plasmonic properties. The observed plasmon emergence phenomena in nanomolecules are of great interest, and the availability of absolutely homogeneous and characterized samples is thus critical to establishing their origin.     

Plasmonic Gold Nanoparticles (AuNPs): Properties,Synthesis and their Advanced Energy,Environmental and Biomedical Applications

Inducing plasmonic characteristics, primarily localized surface plasmon resonance (LSPR), in conventional AuNPs through particle size and shape control could lead to a significant enhancement in electrical, electrochemical, and optical properties. Synthetic protocols and versatile fabrication methods play pivotal roles to produced plasmonic gold nanoparticles (AuNPs), which can be employed in multipurpose energy, environmental and biomedical applications. The main focus of this review is to provide a comprehensive and tutorial overview of various synthetic methods to design highly plasmonic AuNPs, along with a brief essay to understand the experimental procedure for each technique. The latter part of the review is dedicated to the most advanced and recent solar-induced energy, environmental and biomedical applications. The synthesis methods are compared to identify the best possible synthetic route, which can be adopted while employing plasmonic AuNPs for a specific application. The tutorial nature of the review would be helpful not only for expert researchers but also for novices in the field of nanomaterial synthesis and utilization of plasmonic nanomaterials in various industries and technologies.     

Understanding plasmonic catalysis with controlled nanomaterials based on catalytic and plasmonic metals

Recently, it has been established that the localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles can be put toward the acceleration and control of molecular transformations. This field, named plasmonic catalysis, has emerged as a new frontier in nanocatalysis. For metals such as silver (Ag), gold (Au), and copper (Cu), the LSPR excitation can take place in the visible and near-infrared ranges, opening possibilities for the conversion of solar to chemical energy and new/alternative reaction pathways not accessible via conventional, thermally activated catalytic processes. As both catalytic and optical properties can be tuned by controlling several physical and chemical parameters at the nanoscale, design-controlled nanomaterials open the door to unlock the potential of plasmonic catalysis both in terms of fundamental understanding and optimization of performances. In this context, after introducing the fundamentals of plasmonic catalysis, we provide an overview on the current understanding of this field enabled by the utilization of designed-controlled nanostructures based on plasmonic and catalytic metals as model systems. We start by discussing trends in plasmonic catalytic performances and their correlation with nanoparticle size, shape, composition, and structure. Then, we highlight how multimetallic compositions and morphologies containing both catalytic and plasmonic components enables one to extend the use of plasmonic catalysis to metals that are important in catalysis but do not support LSPR excitation in the visible range. Finally, we focus on key challenges and perspectives that are critically important to assist us in designing future energy-efficient plasmonic-catalytic materials.     

Plasmonic Trapping with a Gold Nanopillar

An improved ability to manipulate nanoscale objects could spur the field of nanotechnology. Optical tweezers offer the compelling advantage that manipulation is performed in a non‐invasive manner. However, traditional optical tweezers based on laser beams focused with microscope lenses face limitations due to the diffraction limit, which states that conventional lenses can focus light to spots no smaller than roughly half the wavelength. This has motivated recent work on optical trapping based on the sub‐wavelength field distributions of surface plasmon nanostructures. This approach offers the benefits of higher precision and resolution, and the possibility of large‐scale parallelization. Herein, we discuss the fundamentals of optical manipulation using surface plasmon resonance structures. We describe two important issues in plasmonic trapping: optical design and thermal management strategies. Finally, we describe a surface plasmon nanostructure, consisting of a gold nanopillar that takes these issues into consideration. It is shown to enable the trapping and rotation (manual and passive) of nanoparticles. Methods by which this concept can be extended are discussed.     

Plasmonic properties of silver nanostructures coated with an amorphous silicon-carbon alloy and their applications for sensitive sensing of DNA hybridization

The use of an amorphous silicon-carbon alloy overcoating on silver nanostructures in a localized surface plasmon resonance (LSPR) sensing platform allows for decreasing the detection limit by an order of magnitude as compared to sensors based on gold nanostructures deposited on glass. In addition, silver based multilayer structures show a distinct plasmonic behaviour as compared to gold based nanostructures, which provides the sensor with an increased short-range sensitivity and a decreased long-range sensitivity.     

Multiple Fano resonances in monolayer hexagonal non-close-packed metallic shells

In this study, we first numerically investigate the appearance and properties of multiple Fano resonances in two-dimensional hexagonal non-close-packed arrays of symmetric metallic shells. The coexistence of broad sphere-like plasmon modes formed from the near-field interaction between the individual sphere plasmons and substantially narrower void plasmon modes supported by the inner surface of the individual shell resonant over the same range of energies can produce such Fano resonances. In particular, void and sphere-like plasmon modes of different angular momentum could directly interact without the need of symmetry breaking in the structure. A cost-effective colloidal crystal templating method is utilized to prepare the arrays of the metallic shells with small openings. The effect of the symmetry breaking on the Fano resonances in metallic cup arrays is experimentally and numerically investigated. Further tunability on the Fano resonances is gained by changing the size of the inner dielectric core, hence changing the moment of the void plasmon modes and consequently the resonance frequency. By adopting the polymer dielectric core with gain materials, our study may offer realizable experimental opportunities towards subwavelength low threshold plasmonic lasing.     

Surfactant‐Free Nonaqueous Synthesis of Plasmonic Molybdenum Oxide Nanosheets with Enhanced Catalytic Activity for Hydrogen Generation from Ammonia Borane under Visible Light

Plasmonic materials have drawn emerging interest, especially in nontraditional semiconductor nanostructures with earth‐abundant elements and low resistive loss. However, the actualization of highly efficient catalysis in plasmonic semiconductor nanostructures is still a challenge, owing to the presence of surface‐capping agents in their synthetic procedures. To fulfill this, a facile non‐aqueous procedure was employed to prepare well‐defined molybdenum oxide nanosheets in the absence of surfactants. The obtained MoO_3‐x nanosheets display intense absorption in a wide range attributed to the localized surface plasmon resonances, which can be tuned from the visible to the near‐infrared region. Herein, we demonstrate that such plasmonic semiconductor nanostructures could be used as highly efficient catalysts that dramatically enhance the hydrogen‐generation activity of ammonia borane under visible light irradiation.     

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.