Colloidal gold and silver triangular nanoprisms

Engineering Single Nanopores on Gold Nanoplates by Tuning Crystal Screw Dislocation

Compared with the large variety of solid gold nanostructures, synthetic approaches for their hollow counterparts are limited, largely confined to chemical and irradiation-based etching of preformed nanostructures. In particular, the preparation of through nanopore structures is extremely challenging. Here, a unique strategy for direct synthesis of gold nanopores in solution without the need for sacrificial templates or postsynthesis processing is reported. By controlling the degree of crystal screw dislocation, a single through pore with diameter ranging from sub-nanometer to tens of nanometers, in the center of large gold nanoplates, can be engineered with precision. Ionic current rectification behaviors are observed using the gold nanopore, potentially enabling new capabilities in biosensing, sequencing, and imaging.

A systematic study of triangular silver nanoplates: one-pot green synthesis, chemical stability, and sensing application

While there has been remarkable success in generating silver (Ag) nanoplates, and they have considerable potential applications, their degradation behavior in certain environments remains poorly understood. In the current work, we investigated the chemical stability of triangular Ag nanoplates. A one-step water-based synthesis method regulated by the coordination of ligands to Ag cations was successfully employed to produce triangular Ag nanoplates with a high yield. The Ag nanoplates were irreversibly degraded when they were aged with poly(styrene-4-sulfonate) (PSS) at room temperature, and the corresponding localized surface plasmon resonances (LSPR) of the Ag nanoplates changed as well. In contrast, when the Ag nanoplates were aged with potassium persulfate (KPS), the shape evolution of Ag nanoplates was found to depend on the external temperature, and the Ag nanoplate solutions showed different final colors when different external temperatures were applied. These results exhibit important implications for the behavior of triangular Ag nanoplates in a wide variety of plasmonic applications and can be applied to the colorimetric sensing of the temperature history.

Photochemical formation of chitosan-stabilized near-infrared-absorbing silver Nanoworms: A "Green" synthetic strategy and activity on Gram-negative pathogenic bacteria

A facile, single-step, non-seeded photochemical protocol for producing a new type of anisotropic silver nanostructure, "nanoworms", with curved longer dimensions and smooth, rounded edges. The nanoworms exhibit surface plasmon resonance (SPR) absorption in the near-infrared window (NIRW) region and are stabilized using biocompatible polymer chitosan, rendering biocompatibility and amplified safety for biological utility of the composition. Both NIRW-absorbing nanoworms and visible-absorbing nanospheres herein are attained exclusively by employing green chemistry principles. Contrary to seed-mediated or polyol techniques, the protocol demonstrates the feasibility to selectively synthesize NIRW-absorbing silver nanostructures in a single step and in complete absence of any known reducing agent. The effect of irradiation, pH, and concentration of starting materials on the formation of nanoworms vs nanospheres is investigated in detail and analyzed by optical spectroscopy and electron microscopy. The dominant SPR obtained in the NIRW region of the nanoworms results from anisotropic AgNPs, as opposed to agglomeration. From TEM images, it is also very clear that a strong correlation exists between the SPR peak maximum and the size distribution of the anisotropic nanoworm structures, with SPR peak maximum exhibiting red shift with the increase in the size of the nanoworm population. Although there is significant size variation of different nanoworms of a given population, all samples exhibit remarkable stability. The nanoworms retained their NIRW-absorbing features even at physiological pH and at a constant ionic strength. The nanodispersions also retained their SPR features in King's B medium. Antipathogenic assays reveal that the anisotropic NIRW-absorbing nanoworms exhibit the highest growth inhibition compared to other spherical nanosilver and molecular silver forms on Gram-negative pathogenic bacteria, Pseudomonas syringae pv. maculicola ES4326 and P. syringae pv. tomato DC3000. These results underscore shape effects of AgNPs and suggest that nanoworms favor the adhesion to (curved) rod-shaped Gram-negative bacteria, resulting in the highest inhibition compared to isotropic AgNPs (smaller spheres), sulfa antibiotics (silver sulfadiazine), and silver ions (AgNO₃).

Precise Control of the Lateral and Vertical Growth of Two-Dimensional Ag Nanoplates

Tuning localized surface plasmon resonance (LSPR) is crucial for practical applications of two-dimensional Ag nanoplates (AgNPs) and relies on the precise control of their lateral length or/and thickness. In the present seed-mediated synthetic method, by taking advantage of underpotential deposition (UPD) of Cu on the (111) surfaces of AgNPs, a solely lateral growth of AgNPs was achieved when Cu(NO₃ )₂ was employed, while a vertical growth of AgNPs could be attained by introducing CuCl₂ into our growth solutions. The lateral length and the vertical thickness of the AgNPs could be tuned in the ranges of 115 to nearly 300 nm and 13.4 to around 200 nm, respectively. Along with control of the dimensional size of AgNPs, LSPR could also be tuned in the visible to near infrared range. Plausible growth mechanisms for the precise control of the lateral and vertical growth of AgNPs were proposed.

When lithography meets self-assembly: a review of recent advances in the directed assembly of complex metal nanostructures on planar and textured surfaces

One of the foremost challenges in nanofabrication is the establishment of a processing science that integrates wafer-based materials, techniques, and devices with the extraordinary physicochemical properties accessible when materials are reduced to nanoscale dimensions. Such a merger would allow for exacting controls on nanostructure positioning, promote cooperative phenomenon between adjacent nanostructures and/or substrate materials, and allow for electrical contact to individual or groups of nanostructures. With neither self-assembly nor top-down lithographic processes being able to adequately meet this challenge, advancements have often relied on a hybrid strategy that utilizes lithographically-defined features to direct the assembly of nanostructures into organized patterns. While these so-called directed assembly techniques have proven viable, much of this effort has focused on the assembly of periodic arrays of spherical or near-spherical nanostructures comprised of a single element. Work directed toward the fabrication of more complex nanostructures, while still at a nascent stage, has nevertheless demonstrated the possibility of forming arrays of nanocubes, nanorods, nanoprisms, nanoshells, nanocages, nanoframes, core-shell structures, Janus structures, and various alloys on the substrate surface. In this topical review, we describe the progress made in the directed assembly of periodic arrays of these complex metal nanostructures on planar and textured substrates. The review is divided into three broad strategies reliant on: (i) the deterministic positioning of colloidal structures, (ii) the reorganization of deposited metal films at elevated temperatures, and (iii) liquid-phase chemistry practiced directly on the substrate surface. These strategies collectively utilize a broad range of techniques including capillary assembly, microcontact printing, chemical surface modulation, templated dewetting, nanoimprint lithography, and dip-pen nanolithography and employ a wide scope of chemical processes including redox reactions, alloying, dealloying, phase separation, galvanic replacement, preferential etching, template-mediated reactions, and facet-selective capping agents. Taken together, they highlight the diverse toolset available when fabricating organized surfaces of substrate-supported nanostructures.

Synthesis of triangular silver nanoprisms and spectroscopic analysis on the interaction with bovine serum albumin

The interactions of triangular silver nanoprisms (TAgNPrs) with bovine serum albumin (BSA) were investigated using multiple spectroscopic techniques. A noticeable absorbance increase was noted in the peak ranges of 250 to 300 nm for BSA, and the intensity increased with the increasing concentration of TAgNPrs. Furthermore, a slight blue shift of the surface plasmon resonance band of TAgNPrs occurred, indicating that the protein absorbed on the TAgNPrs surface to form a bio-nano interface. Analysis of fluorescence quenching data using the Stern-Volmer method revealed that static quenching takes place with complex formation. Evaluation of thermodynamic parameter ΔG ^θ for the binding processes indicated that the binding reaction was exothermic. Furthermore, the values of binding constant K revealed that the size of nanoparticles can affect the binding degree. The order of binding affinity is 43.7 nm > 36.2 nm > 25.1 nm. The competitive experiments of site markers (flufenamic acid and phenylbutazone) suggested that the binding site of TAgNPrs on BSA was located in the region of subdomain IIIA (Sudlow site II). In addition, the conformational changes of BSA by TAgNPrs were analyzed by using synchronous fluorescence spectra, circular dichroism, and three-dimensional fluorescence spectra. Graphical abstract The protein absorbed on the TAgNPrs surface to form a nanoparticle-protein corona.

The Effect of shape on Cellular Uptake of Gold Nanoparticles in the forms of Stars, Rods, and Triangles

Gold nanomaterials have attracted considerable interest as vehicles for intracellular drug delivery. In our study, we synthesized three different shapes of methylpolyethylene glycol coated-anisotropic gold nanoparticles: stars, rods, and triangles. The cellular internalization of these nanoparticles by RAW264.7 cells was analyzed, providing a parametric evaluation of the effect of shape. The efficiency of cellular uptake of the gold nanoparticles was found to rank in the following order from lowest to highest: stars, rods, and triangles. The possible mechanisms of cellular uptake for the three types of gold nanoparticles were examined, and it was found that different shapes tended to use the various endocytosis pathways in different proportions. Our study, which has demonstrated that shape can modulate the uptake of nanoparticles into RAW264.7 cells and that triangles were the shape with the most efficient cellular uptake, provides useful guidance toward the design of nanomaterials for drug delivery.

Antibacterial properties and toxicity from metallic nanomaterials

The era of antibiotic resistance is a cause of increasing concern as bacteria continue to develop adaptive countermeasures against current antibiotics at an alarming rate. In recent years, studies have reported nanoparticles as a promising alternative to antibacterial reagents because of their exhibited antibacterial activity in several biomedical applications, including drug and gene delivery, tissue engineering, and imaging. Moreover, nanomaterial research has led to reports of a possible relationship between the morphological characteristics of a nanomaterial and the magnitude of its delivered toxicity. However, conventional synthesis of nanoparticles requires harsh chemicals and costly energy consumption. Additionally, the exact relationship between toxicity and morphology of nanomaterials has not been well established. Here, we review the recent advancements in synthesis techniques for silver, gold, copper, titanium, zinc oxide, and magnesium oxide nanomaterials and composites, with a focus on the toxicity exhibited by nanomaterials of multidimensions. This article highlights the benefits of selecting each material or metal-based composite for certain applications while also addressing possible setbacks and the toxic effects of the nanomaterials on the environment.

Intermetallic Nanocrystals: Syntheses and Catalytic Applications

At the forefront of nanochemistry, there exists a research endeavor centered around intermetallic nanocrystals, which are unique in terms of long-range atomic ordering, well-defined stoichiometry, and controlled crystal structure. In contrast to alloy nanocrystals with no elemental ordering, it is challenging to synthesize intermetallic nanocrystals with a tight control over their size and shape. Here, recent progress in the synthesis of intermetallic nanocrystals with controllable sizes and well-defined shapes is highlighted. A simple analysis and some insights key to the selection of experimental conditions for generating intermetallic nanocrystals are presented, followed by examples to highlight the viable use of intermetallic nanocrystals as electrocatalysts or catalysts for various reactions, with a focus on the enhanced performance relative to their alloy counterparts that lack elemental ordering. Within the conclusion, perspectives on future developments in the context of synthetic control, structure-property relationships, and applications are discussed.

Gold Nanotriangle Formation through Strong-Field Laser Processing of Aqueous KAuCl4 and Postirradiation Reduction by Hydrogen Peroxide

Femtosecond laser irradiation of aqueous KAuCl₄ followed by postirradiation reduction with hydrogen peroxide (H₂O₂) is investigated as a new approach for the synthesis of gold nanotriangles (AuNTs) without any added surfactant molecules. Laser irradiation was applied for times ranging from 5 to 240 s, and postirradiation reduction of the solutions was monitored by UV-vis spectroscopy. Laser processing of aqueous KAuCl₄ for 240 s, where the full reduction of Au(III) occurred during irradiation, produced spherical gold nanoparticles (AuNPs) with an average size of 11.4 ± 3.4 nm. Irradiation for shorter times (i.e., 15 s) resulted in the formation of laser-generated AuNP seeds (5.7 ± 1.8 nm) in equilibrium with unreacted KAuCl₄ after termination of laser irradiation. The postirradiation reduction of these solutions by H₂O₂ produced a mixture of spherical and triangular AuNPs. Decreasing the laser irradiation time from 45 to 5 s significantly reduced the number of laser-generated Au seeds, the amount of H₂O₂ produced, and the rate of postirradiation reduction, resulting in the formation of a large number of AuNTs with sizes increasing from 29.5 ± 10.2 to 125 ± 43.2 nm. Postirradiation reduction is kinetically inhibited in the absence of laser-generated AuNP seeds.

Controllable Biosynthesis and Properties of Gold Nanoplates Using Yeast Extract

ABSTRACT

Biosynthesis of gold nanostructures has drawn increasing concerns because of its green and sustainable synthetic process. However, biosynthesis of gold nanoplates is still a challenge because of the expensive source and difficulties of controllable formation of morphology and size. Herein, one-pot biosynthesis of gold nanoplates is proposed, in which cheap yeast was extracted as a green precursor. The morphologies and sizes of the gold nanostructures can be controlled via varying the pH value of the biomedium. In acid condition, gold nanoplates with side length from 1300 ± 200 to 300 ± 100 nm and height from 18 to 15 nm were obtained by increasing the pH value. Whereas, in neutral or basic condition, only gold nanoflowers and nanoparticles were obtained. It was determined that organic molecules, such as succinic acid, lactic acid, malic acid, and glutathione, which are generated in metabolism process, played important role in the reduction of gold ions. Besides, it was found that the gold nanoplates exhibited plasmonic property with prominent dipole infrared resonance in near-infrared region, indicating their potential in surface plasmon-enhanced applications, such as bioimaging and photothermal therapy.

Highly dispersed Ag/TiO2via adsorptive self-assembly for bactericidal application

The strong electrostatic adsorption (SEA) technique was used for the preparation of Ag/TiO₂by driving the Ag precursor onto the TiO₂surface.

Branched Ag nanoplates: synthesis dictated by suppressing surface diffusion and catalytic activity for nitrophenol reduction

Highly branched Ag nanoplates were achieved at extremely low Ag atoms surface diffusion rate, fulfilledviathe Cu under potential deposition.

Seed-Mediated Growth of Colloidal Metal Nanocrystals

Seed-mediated growth is a powerful and versatile approach for the synthesis of colloidal metal nanocrystals. The vast allure of this approach mainly stems from the staggering degree of control one can achieve over the size, shape, composition, and structure of nanocrystals. These parameters not only control the properties of nanocrystals but also determine their relevance to, and performance in, various applications. The ingenuity and artistry inherent to seed-mediated growth offer extensive promise, enhancing a number of existing applications and opening the door to new developments. This Review demonstrates how the diversity of metal nanocrystals can be expanded with endless opportunities by using seeds with well-defined and controllable internal structures in conjunction with a proper combination of capping agent and reduction kinetics. New capabilities and future directions are also highlighted.

Colloidal Synthesis and Applications of Plasmonic Metal Nanoparticles

Plasmonic metal nanoparticles attract intense research attention because of their fascinating surface plasmon resonance properties and their potential applications in diverse fields. Here, some of the recent research efforts on the synthesis and applications of plasmonic metal nanoparticles are highlighted. Starting from the colloidal synthesis of metal nanoparticles, various shaped silver and gold nanostructures are discussed. The applications of plasmonic nanoparticles in photocatalysis, surface-enhanced Raman spectroscopy (SERS), and devices are used as excellent examples showcasing the advantages of these nanoparticles. The report closes with a brief summary and discussion on the challenges and future direction in this research field.

Out-of-Substrate Ag-Ag2O Nanoplates: Surfactantless Photochemical Synthesis, Structural Evolution, and Mechanistic Study

Two types of out-of-substrate Ag-Ag2O nanoplates were grown on a ZnO substrate through a surfactantless photochemical method. First, the in situ photochemically synthesized Ag-Ag2O nanoparticles further crystallized into nanoplate-like superstructures with rough surfaces and ragged edges. The nanoparticle-mediated crystallization process was governed by a layer-by-layer crystallization mechanism. Our study should help fundamentally understand the formation mechanism of hierarchical nanoparticle superstructures. Under continuous UV illumination, the hundreds of nanometer-sized rough nanoplates (i.e., the nanoplate-like superstructures of nanoparticles) can be transformed into large smooth nanoplates with sizes of up to several micrometers. The out-of-substrate Ag-Ag2O nanoplates/ZnO heterostructures are potentially promising for photocatalytic applications.

Silica-coated triangular gold nanoprisms as distance-dependent plasmon-enhanced fluorescence-based probes for biochemical applications

Plasmon-enhanced fluorescence (PEF)-based anisotropic nanostructures are considered extremely promising tools for improving the inherent problems of traditional fluorophores and for detecting important biomolecules with high sensitivity. Herein, a novel triangular gold nanoprism (AuNPR)-based fluorescence probe, AuNPR@SiO₂@12,17-tetramethyl-3-dihydro-(2s-trans)-thyl-7(Ce6), was developed for PEF by virtue of multiple "hot spots" of AuNPRs. Fluorescence enhancement of fluorophores can be realized owing to the larger and stronger electromagnetic fields located at the sharp tips of AuNPRs than those on spherical particles and nanorods. A silica shell was employed as a rigid spacer to precisely adjust the distance between the AuNPR and Ce6 for optimal PEF. Owing to the improved fluorescence signal, core-shell PEF-based AuNPRs can be applied as a turn-on probe for highly selective and sensitive detection of pyrophosphate (PPi) with a desirable detection limit of 0.2 μM using a displacement approach. Meanwhile, we demonstrated that these nanomaterials have great potential for real-time monitoring of polymerase chain reaction (PCR) products, successfully revealing an approximately 240 times higher detectable fluorescence response than that of traditional gel electrophoresis. Furthermore, cell imaging indicates the potential applications of PEF-based probes in living cells.

Role of shape in substrate-induced plasmonic shift and mode uncovering on gold nanocrystals

A number of plasmonic devices and applications, such as chemical and biological sensors, plasmon-enhanced solar cells, optical nanoantennas, metamaterials and metasurfaces, require the deposition of plasmonic metal nanocrystals on various substrates. Because the localized plasmon resonance modes, energies and strengths are strongly dependent on the dielectric function of the surrounding environment, the substrate is expected to largely affect the plasmonic properties of supported metal nanocrystals. Therefore, understanding the effects of the substrate on the plasmonic properties of metal nanocrystals and the roles of the involved factors will be crucial for designing various plasmonic devices that are made of metal nanocrystals deposited on different substrates. Herein we report on our study and results of the effects of substrates with distinct dielectric functions on the plasmonic properties of three types of Au nanocrystals. A combination of experiments and numerical simulations shows that the presence of a substrate causes plasmonic shifts as well as the appearance of new plasmon modes. The plasmonic shifts and the emergence of new plasmon modes are found to be dependent on the particle shape of Au nanocrystals and in turn on the fractional particle surface area that is in contact with the supporting substrate. For Au nanospheres and nanorods, plasmonic shifts, less than 100 nm, are observed on the scattering spectra by changing the supporting substrate from indium tin oxide to silicon. In comparison, a giant spectral shift of more than 300 nm is obtained for Au nanoplates. Moreover, silicon substrates induce the emergence of an out-of-plane quadrupolar mode of Au nanoplates, which interacts with an out-of-plane octupolar mode to give rise to a distinct Fano resonance. The Fano resonance is found to become stronger as the thickness of Au nanoplates is decreased. These results are of great importance for understanding the plasmonic properties of noble metal nanocrystals supported on various substrates, and for designing novel plasmonic nanostructures with desired optical properties and functions.

The nature and implications of uniformity in the hierarchical organization of nanomaterials

In this Perspective, we present a framework that defines how to understand and control material structure across length scales with inorganic nanoparticles. Three length scales, frequently discussed separately, are unified under the topic of hierarchical organization: atoms arranged into crystalline nanoparticles, ligands arranged on nanoparticle surfaces, and nanoparticles arranged into crystalline superlattices. Through this lens, we outline one potential pathway toward perfect colloidal matter that emphasizes the concept of uniformity. Uniformity is of both practical and functional importance, necessary to increase structural sophistication and realize the promise of nanostructured materials. Thus, we define the nature of nonuniformity at each length scale as a means to guide ongoing research efforts and highlight potential problems in the field.

Structural and Optical Properties of Discrete Dendritic Pt Nanoparticles on Colloidal Au Nanoprisms

Catalytic and optical properties can be coupled by combining different metals into nanoscale architectures in which both the shape and the composition provide fine-tuning of functionality. Here, discrete, small Pt nanoparticles (diameter = 3-6 nm) were grown in linear arrays on Au nanoprisms, and the resulting structures are shown to retain strong localized surface plasmon resonances. Multidimensional electron microscopy and spectroscopy techniques (energy-dispersive X-ray spectroscopy, electron tomography, and electron energy-loss spectroscopy) were used to unravel their local composition, three-dimensional morphology, growth patterns, and optical properties. The composition and tomographic analyses disclose otherwise ambiguous details of the Pt-decorated Au nanoprisms, revealing that both pseudospherical protrusions and dendritic Pt nanoparticles grow on all faces of the nanoprisms (the faceted or occasionally twisted morphologies of which are also revealed), and shed light on the alignment of the Pt nanoparticles. The electron energy-loss spectroscopy investigations show that the Au nanoprisms support multiple localized surface plasmon resonances despite the presence of pendant Pt nanoparticles. The plasmonic fields at the surface of the nanoprisms indeed extend into the Pt nanoparticles, opening possibilities for combined optical and catalytic applications. These insights pave the way toward comprehensive nanoengineering of multifunctional bimetallic nanostructures, with potential applications in plasmon-enhanced catalysis and in situ monitoring of chemical processes via surface-enhanced spectroscopy.

Surface area-dependent second harmonic generation from silver nanorods

The nonlinear optical (NLO) properties of metallic nanoparticles strongly depend on their size and shape. Metallic gold nanorods have already been widely investigated, but other noble metals could also be used for nanorod fabrication towards applications in photonics. Here we report on the synthesis and NLO characterization of silver nanorods (AgNRs) with controllable localized surface plasmon resonance. We have implemented an original, one-step and seedless synthesis method, based on a spontaneous particle growth technique in the presence of polyvinylpyrrolidone (PVP) as a capping agent. Colloidal solutions of AgNRs with various aspect ratios (5.0; 6.3; 7.5; 8.2 and 9.7) have been obtained and characterized using Harmonic light scattering (HLS) at 1064 nm, in order to investigate their quadratic NLO properties. From HLS experiments, we demonstrate that hyperpolarizability (β) values of AgNRs display a strong dependence on their surface area.

Linear dichroism and optical anisotropy of silver nanoprisms in polymer films

We present optical studies of two different size distributions of silver triangular nanoprisms, one with a dipole resonance at 520 nm and the other with a dipole resonance at 650 nm, placed in different media. Significant wavelength-dependent depolarization of scattered light from the silver nanoprisms suspended in water indicates strong interference of multiple surface plasmon resonant modes in the same particle. We use this depolarization as a probe of light scattering by the nanoprisms in a lipid solution due to the rejection of a polarized background scattering. Also, the silver nanoprisms were embedded in a polyvinyl alcohol polymer matrix and oriented by stretching the polymer/nanoprism nanocomposite films. We observe significantly increased linear dichroism in the region associated with the plasmonic in-plane dipole mode upon stretching. Additionally, there is a weaker linear dichroism in the region associated with out-of-plane modes, which vanish in the extinction spectrum of the stretched nanocomposite film.

Polyvinylpyrrolidone-induced anisotropic growth of gold nanoprisms in plasmon-driven synthesis

After more than a decade, it is still unknown whether the plasmon-mediated growth of silver nanostructures can be extended to the synthesis of other noble metals, as the molecular mechanisms governing the growth process remain elusive. Herein, we demonstrate the plasmon-driven synthesis of gold nanoprisms and elucidate the details of the photochemical growth mechanism at the single-nanoparticle level. Our investigation reveals that the surfactant polyvinylpyrrolidone preferentially adsorbs along the nanoprism perimeter and serves as a photochemical relay to direct the anisotropic growth of gold nanoprisms. This discovery confers a unique function to polyvinylpyrrolidone that is fundamentally different from its widely accepted role as a crystal-face-blocking ligand. Additionally, we find that nanocrystal twinning exerts a profound influence on the kinetics of this photochemical process by controlling the transport of plasmon-generated hot electrons to polyvinylpyrrolidone. These insights establish a molecular-level description of the underlying mechanisms regulating the plasmon-driven synthesis of gold nanoprisms.

Seedless synthesis of gold nanorods using resveratrol as a reductant

Gold nanorods (GNRs) attract extensive attention in current diagnostic and therapeutic applications which require the synthesis of GNRs with high yields, adjustable aspect ratio, size monodispersity, and easy surface decoration. In the seed-mediated synthesis of GNRs using cetyl trimethyl ammonium bromide (CTAB) micelles as templates, the additives of aromatic compounds have been found to be important for improving the size monodispersity of the as-synthesized GNRs; this is hopeful in terms of the further optimization of the synthetic methodology of GNRs. In this work, resveratrol, a natural polyphenol in grapes with an anti-oxidization behavior, is employed as the reductant for the seedless synthesis of GNRs with a good size monodispersity and a tunable aspect ratio. Accordingly, the longitudinal localized surface plasmon resonance (LSPR) peak is tunable from 570 to 950 nm. The success of our approach is attributed to the aromatic structure and mild reducibility of resveratrol. The embedment of resveratrol into CTAB micelles strengthens the facet-selective adsorption of CTAB, and therewith facilitates the anisotropic growth of GNRs. In addition, the mild reducibility of resveratrol is capable of supporting GNR growth by avoiding secondary nucleation, thus allowing the seedless synthesis of GNRs with a good size monodispersity. As a chemopreventive agent, the combination of resveratrol in GNR synthesis will consolidate the theranostic applications of GNRs.

Seed-mediated growth of Au nanorings with size control on Pd ultrathin nanosheets and their tunable surface plasmonic properties

Nanorings made of noble metals such as Au and Ag have attracted particular interest in plasmonic properties since they allow remarkable tunability of plasmon resonance wavelengths associated with their unique structural features. Unfortunately, most of the syntheses for Au nanorings involve complex procedures and/or require highly specialized and expensive facilities. Here, we report a seed-mediated approach for selective deposition of Au nanorings on the periphery of Pd seeds with the structure of an ultrathin nanosheet through the island growth mode. In combination with selective etching of Pd nanosheets, Au nanorings are eventually produced. We can control the outer diameter and wall thickness of the nanorings by simply varying the size of the Pd nanosheets and reaction time. By taking the advantage of this size controllability, the nanorings show tunable surface plasmonic properties in the near infrared (NIR) region arising from both the in-plane dipole and face resonance modes. Owing to their good surface plasmonic properties, the nanorings show substantially enhanced surface-enhanced Raman spectroscopy (SERS) performance for rhodamine 6G, and are therefore confirmed as good SERS substrates to detect trace amounts of molecules.

Nanoparticle shape, thermodynamics and kinetics

Nanoparticles can be beautiful, as in stained glass windows, or they can be ugly as in wear and corrosion debris from implants. We estimate that there will be about 70,000 papers in 2015 with nanoparticles as a keyword, but only one in thirteen uses the nanoparticle shape as an additional keyword and research focus, and only one in two hundred has thermodynamics. Methods for synthesizing nanoparticles have exploded over the last decade, but our understanding of how and why they take their forms has not progressed as fast. This topical review attempts to take a critical snapshot of the current understanding, focusing more on methods to predict than a purely synthetic or descriptive approach. We look at models and themes which are largely independent of the exact synthetic method whether it is deposition, gas-phase condensation, solution based or hydrothermal synthesis. Elements are old dating back to the beginning of the 20th century-some of the pioneering models developed then are still relevant today. Others are newer, a merging of older concepts such as kinetic-Wulff constructions with methods to understand minimum energy shapes for particles with twins. Overall we find that while there are still many unknowns, the broad framework of understanding and predicting the structure of nanoparticles via diverse Wulff constructions, either thermodynamic, local minima or kinetic has been exceedingly successful. However, the field is still developing and there remain many unknowns and new avenues for research, a few of these being suggested towards the end of the review.

Clusters of polyhedra in spherical confinement

Dense particle packing in a confining volume remains a rich, largely unexplored problem, despite applications in blood clotting, plasmonics, industrial packaging and transport, colloidal molecule design, and information storage. Here, we report densest found clusters of the Platonic solids in spherical confinement, for up to [Formula: see text] constituent polyhedral particles. We examine the interplay between anisotropic particle shape and isotropic 3D confinement. Densest clusters exhibit a wide variety of symmetry point groups and form in up to three layers at higher N. For many N values, icosahedra and dodecahedra form clusters that resemble sphere clusters. These common structures are layers of optimal spherical codes in most cases, a surprising fact given the significant faceting of the icosahedron and dodecahedron. We also investigate cluster density as a function of N for each particle shape. We find that, in contrast to what happens in bulk, polyhedra often pack less densely than spheres. We also find especially dense clusters at so-called magic numbers of constituent particles. Our results showcase the structural diversity and experimental utility of families of solutions to the packing in confinement problem.

Magnetically tunable colloidal micromirrors

Herein we demonstrate a method for decorating highly reflective 2D gold microplates with magnetic nanoparticles to produce an optical colloid that can be actuated using an applied magnetic field. These magnetic micromirrors can be rapidly rotated and exhibit a strong contrast in reflectance between the "on" and "off" states.

Glucose-functionalized Au nanoprisms for optoacoustic imaging and near-infrared photothermal therapy

Targeted imaging and tumor therapy using nanomaterials has stimulated research interest recently, but the high cytotoxicity and low cellular uptake of nanomaterials limit their bioapplication. In this paper, glucose (Glc) was chosen to functionalize Au nanoprisms (NPrs) for improving the cytotoxicity and cellular uptake of Au@PEG-Glc NPrs into cancer cells. Glucose is a primary source of energy at the cellular level and at cellular membranes for cell recognition. A coating of glucose facilitates the accumulation of Au@PEG-Glc NPrs in a tumor region much more than Au@PEG NPrs. Due to the high accumulation and excellent photoabsorbing property of Au@PEG-Glc NPrs, enhanced optoacoustic imaging of a tumor in vivo was achieved, and visualization of the tumor further guided cancer treatment. Based on the optical-thermal conversion performance of Au@PEG-Glc NPrs, the tumor in vivo was effectively cured through photothermal therapy. The current work demonstrates the great potential of Au@PEG-Glc NPrs in optoacoustic imaging and photothermal cancer therapy in future.