Gold Nanocages: Engineering Their Structure for Biomedical Applications

The galvanic replacement reaction between a Ag template and HAuCl₄ in an aqueous solution transforms 30–200 nm Ag nanocubes into Au nanoboxes and nanocages (nanoboxes with porous walls). By controlling the molar ratio of Ag to HAuCl₄, the extinction peak of resultant structures can be continuously tuned from the blue (400 nm) to the near‐infrared (1200 nm) region of the electromagnetic spectrum. These hollow Au nanostructures are characterized by extraordinarily large cross‐sections for both absorption and scattering. Optical coherence tomography measurements indicate that the 36 nm nanocage has a scattering cross‐section of ～ 0.8 × 10^–15 m² and an absorption cross‐section of ～ 7.3 × 10^–15 m². The absorption cross‐section is more than five orders of magnitude larger than those of conventional organic dyes. Exposure of Au nanocages to a camera flash resulted in the melting and conversion of Au nanocages into spherical particles due to photothermal heating. Discrete‐dipole‐approximation calculations suggest that the magnitudes of both scattering and absorption cross‐sections of Au nanocages can be tailored by controlling their dimensions, as well as the thickness and porosity of their walls. This novel class of hollow nanostructures is expected to find use as both a contrast agent for optical imaging in early stage tumor detection and as a therapeutic agent for photothermal cancer treatment.     

Dark-field microscopy studies of single metal nanoparticles: understanding the factors that influence the linewidth of the localized surface plasmon resonance

This article provides a review of our recent Rayleigh scattering measurements on single metal nanoparticles. Two different systems will be discussed in detail: gold nanorods with lengths between 30 and 80 nm, and widths between 8 and 30 nm; and hollow gold-silver nanocubes (termed nanoboxes or nanocages depending on their exact morphology) with edge lengths between 100 and 160 nm, and wall thicknesses of the order of 10 nm. The goal of this work is to understand how the linewidth of the localized surface plasmon resonance depends on the size, shape, and environment of the nanoparticles. Specifically, the relative contributions from bulk dephasing, electron-surface scattering, and radiation damping (energy loss via coupling to the radiation field) have been determined by examining particles with different dimensions. This separation is possible because the magnitude of the radiation damping effect is proportional to the particle volume, whereas, the electron-surface scattering contribution is inversely proportional to the dimensions. For the nanorods, radiation damping is the dominant effect for thick rods (widths greater than 20 nm), while electron-surface scattering is dominant for thin rods (widths less than 10 nm). Rods with widths in between these limits have narrow resonances-approaching the value determined by the bulk contribution. For nanoboxes and nanocages, both radiation damping and electron-surface scattering are significant at all sizes. This is because these materials have thin walls, but large edge lengths and, therefore, relatively large volumes. The effect of the environment on the localized surface plasmon resonance has also been studied for nanoboxes. Increasing the dielectric constant of the surroundings causes a red-shift and an increase in the linewidth of the plasmon band. The increase in linewidth is attributed to enhanced radiation damping.     

Fabrication of cubic nanocages and nanoframes by dealloying Au/Ag alloy nanoboxes with an aqueous etchant based on Fe(NO3)3 or NH4OH

This paper describes a two-step procedure for generating cubic nanocages and nanoframes. In the first step, Au/Ag alloy nanoboxes were synthesized through the galvanic replacement reaction between Ag nanocubes and an aqueous HAuCl4 solution. The second step involved the selective removal (or dealloying) of Ag from the alloy nanoboxes with an aqueous etchant based on Fe(NO3)3 or NH4OH. The use of a wet etchant other than HAuCl4 for the dealloying process allows one to better control the wall thickness and porosity of resultant nanocages because there is no concurrent deposition of Au. By increasing the amount of Fe(NO3)3 or NH4OH added to the dealloying process, nanoboxes derived from 50-nm Ag nanocubes could be converted into nanocages and then cubic nanoframes with surface plasmon resonance (SPR) peaks continuously shifted from the visible region to 1200 nm. It is also possible to obtain nanocages with relatively narrow SPR peaks (with a full width at half-maximum as small as 180 nm) by controlling the amount of HAuCl4 used for the galvanic replacement reaction and thus the optimization of the percentage of Au in the alloy nanoboxes.     

Synthesis of silica nanoboxes via a simple hard-template method and their application in controlled release

Silica nanoboxes have been successfully synthesized via a simple hard-template method at room temperature. The MnCO₃ nanocubes are firstly employed as the hard template. Scanning electron microscopy (SEM) is used to characterize silica nanoboxes and indicates the hollow structure of products. The shell thickness of nanoboxes can be well controlled by the amount of tetraethylorthosilicate (TEOS) and the surface area is calculated through the N₂ adsorption-desorption isotherm. Based on these results, a plausible mechanism is proposed to explain the formation of silica nanoboxes. In addition, preliminary tests demonstrate that the silica nanoboxes are capable of being loaded and releasing Rhodamine B, thus showing a great potential in the controlled delivery applications.     

Magnetic properties and transmission electron microscopy studies of Ni nanoparticles encapsulated in carbon nanocages and carbon nanotubes

Three types of carbon nanomaterials, including bamboo-shaped carbon nanotubes with Ni encapsulated and hollow and Ni catalytic particles filled carbon nanocages, have been prepared by methane catalytic decomposition at a relatively low temperature. Transmission electron microscopy observations showed that fascinating fullerene-like Ni–C (graphitic) core–shell nanostructures predominated. Detailed examination of high-resolution transmission electron microscopy showed that the walls of bamboo-shaped carbon nanotubes with quasi-cone catalytic particles encapsulated consisted of oblique graphene planes with respect to the tube axis. The Ni particles encapsulated in the carbon nanocages were larger than that encapsulated in carbon nanotubes, but the diameters of the cores of hollow carbon nanocages were less than that of Ni particles encapsulated in carbon nanotubes, suggesting that the sizes of catalyst particles played an important role during carbon nanomaterial growth. The magnetic properties of the carbon nanomaterials were measured, which showed relatively large coercive force (H_c = 138.4 O_e) and good ferromagnetism (M_r/M_s = 0.325).     

Oxalate-Assisted Synthesis of Hollow Carbon Nanocage With Fe Single Atoms for Electrochemical CO2 Reduction

Metal single-atom catalysts are promising in electrochemical CO₂ reduction reaction (CO₂RR). The pores and cavities of the supports can promote the exposure of active sites and mass transfer of reactants, hence improve their performance. Here, iron oxalate is added to ZIF-8 and subsequently form hollow carbon nanocages during calcination. The formation mechanism of the hollow structure is studied in depth by controlling variables during synthesis. Kirkendall effect is the main reason for the formation of hollow porous carbon nanocages. The hollow porous carbon nanocages with Fe single atoms exhibit better CO₂RR activity and CO selectivity. The diffusion of CO₂ facilitated by the mesoporous structure of carbon nanocage results in their superior activity and selectivity. This work has raised an effective strategy for the synthesis of hollow carbon nanomaterials, and provides a feasible pathway for the rational design of electrocatalysts for small molecule activation.     

Hollow carbon nanostructures obtained from hydrothermal carbonization of lignocellulosic biomass

Here we describe a new method for obtaining carbon nanocages at relatively low temperatures using a low-cost lignocellulosic waste material as carbon precursor. Coconut coir dust has been submitted to hydrothermal carbonization in the presence of clays minerals such as sepiolite, attapulgite, and montmorillonite followed by a demineralization step. Just after hydrothermal treatment, the samples prepared in the absence of the clays presented a sponge-like morphology as typically described for hard-plant tissues submitted to this treatment while the samples heated in the presence of clays were fundamentally heterogeneous. After chemical etching with hydrofluoric acid, the sample free from clays exhibited irregular round-shaped particles with poorly defined cavities. For samples containing clays, on the other hand, the chemical etching lead to well-defined carbon nanocages as long as the particles were successfully etched such as attapulgite and montmorillonite. For sepiolite, however, the presence of residual inorganic particles was observed along with irregularly shaped hollow nanostructures. Finally, Raman measurements revealed the typical features of amorphous carbons.     

Multifunctional hollow mesoporous silica nanocages for cancer cell detection and the combined chemotherapy and photodynamic therapy

Highly uniform and multifunctional hollow mesoporous silica nanocages that combined excellent properties (good biocompatibility, fluorescence imaging, drug delivery, and dual-mode cancer therapy) in one single system were synthesized. Dye molecules labeled in the nanocages could be used as traceable detectors in fluorescence imaging. A chemotherapeutic drug, doxorubicin (DOX), has been loaded into the nanocages with a high storage capacity due to the large cubic cavities and could be released through the penetrating mesoporous channels in a sustained fashion. Hematoporphyrin molecules were also covalently doped in the nanocages and allowed for photodynamic therapy. More importantly, a cooperative, synergistic therapy combining chemotherapy and photodynamic therapy exhibited high therapeutic efficacy for cancer therapy in vitro.     

Ce-doped hollow In2O3 nanoboxes derived from metal–organic frameworks with excellent formaldehyde-sensing performance

In recent years, metal oxides derived from metal organic frameworks (MOFs) have been widely used in the gas-sensing direction due to their regular framework structure and large porosity. At the same time, rare earth ion doping can also effectively improve the gas-sensing properties of metal oxide semiconductors. Herein, we report the synthesis of MOFs-drived Ce-doped In₂O₃ samples by calcining precursors prepared by a simple oil bath method. The experimental characterization results show that the as-prepared samples exhibit uniform hollow nanoboxes with high surface area (48.5 m²/g) and abundant oxygen vacancies. Owing to the unique structures, the 1 wt% Ce-doped In₂O₃ nanobox-based gas sensor shows a fast response (1 s), quick recovery (1 s), and an ultralow detection limit (response of 13.4 for 1 ppm of formaldehyde) at the low operating temperature (140 °C). The excellent gas-sensing performance is mainly attributed to hollow structure and the incorporation of Ce, increasing the number of oxygen vacancies and adsorbed oxygen in improving formaldehyde sensing performance of In₂O₃ sensors. This kind of rare earth ion-doped hollow nanoboxes derived from MOFs provides a strategy for the design and development of high performance gas sensor.

     

3D Graphene Encapsulated Hollow CoSnO3 Nanoboxes as a High Initial Coulombic Efficiency and Lithium Storage Capacity Anode

3D Graphene sheets encapsulated amorphous hollow CoSnO₃ nanoboxes (H‐CoSnO₃@reduced graphene oxide [RGO]) are successfully fabricated by first preparing 3D graphene oxides encapsulated solid CoSn(OH)₆ nanocubes, followed by an alkaline etching process and subsequent heating treatment in Ar. The hollow CoSnO₃ nanoboxes with average particle size of 230 nm are uniformly and tightly encapsulated by RGO sheets. As an anode material for Li‐ion batteries, H‐CoSnO₃@RGO displays high initial Coulombic efficiency of 87.1% and large reversible capacity of 1919 mA h g^?1 after 500 cycles at the current density of 500 mA g^?1. Moreover, excellent rate capability (1250, 1188, 1141, 1115, 1086, 952, 736, and 528 mA h g^?1 at 100, 200, 300, 400, 500, 1000, 2000, and 5000 mA g^?1, respectively) is acquired. The reasons for excellent lithium storage properties of H‐CoSnO₃@RGO are discussed in detail.     

Chemically synthesized hollow nanostructures in iron oxides

In this work, we report a detailed study of the formation of hollow nanostructures in iron oxides. Core/shell Fe/Fe-oxide nanoparticles were synthesized by thermal decomposition of Fe(CO)(5) at high temperature. It was found that 8 nm is the critical size above which the particles have a core/shell morphology, whereas below this size the particles exhibit a hollow morphology. Annealing the core/shell particles under air also leads to the formation of hollow spheres with a significant increase in the average particle size. In the case of the thermally activated Kirkendall process, the particles do not fully transform into hollow structures but many irregular shaped voids exist inside each particle. The 8 nm hollow particles are superparamagnetic at room temperature with a blocking temperature of 70 K whereas the core/shell particles are ferromagnetic.     

Amorphous Ni(OH)2 Nanoboxes: Fast Fabrication and Enhanced Sensing for Glucose

Inspired by Pearson's hard and soft acid‐base (HSAB) principle, uniform amorphous Ni(OH)₂ nanoboxes with intact shell structures and various sizes are quickly fabricated by deliberately selecting S₂O₃^2? as the coordinating etchant toward Cu₂O templates and optimizing the reaction conditions. It is found that not only the solvent system but also the employing of a surfactant is vital for the fabrication of the nanoboxes. Ni(OH)₂ nanoboxes, as an example, demonstrate an improved electrochemical sensing ability for glucose, which might be due to their amorphous and hollow structural features.     

Highly nonlinear solitary waves in chains of hollow spherical particles

We study the dynamic response of one- dimensional granular chains composed of uniform hollow spheres excited by an impulse, and we observe the formation and propagation of highly nonlinear solitary waves. We find that the dynamics of these solitary waves are different from the solitary waves forming in chains composed of uniform solid spheres, because of the changes in the contact interaction between particles. We study the quasi-static contact interaction between two hollows spheres using finite element (FE) simulations, and approximate their response as a power-law type function in the range of forces of interest for this work. The experimental data obtained by testing a chain of particles shows good agreement with theoretical predictions obtained using a long wavelength approximation, and with numerical simulations based on discrete particle and FE models. We also investigate the effect of hollow spheres’ wall thickness on the dynamic response of the chains.     

Carbon-Based Nanocages: A New Platform for Advanced Energy Storage and Conversion

Energy storage and conversion play a crucial role in modern energy systems, and the exploration of advanced electrode materials is vital but challenging. Carbon-based nanocages consisting of sp² carbon shells feature a hollow interior cavity with sub-nanometer microchannels across the shells, high specific surface area with a defective outer surface, and tunable electronic structure, much different from the intensively studied nanocarbons such as carbon nanotubes and graphene. These structural and morphological characteristics make carbon-based nanocages a new platform for advanced energy storage and conversion. Up-to-date synthetic strategies of carbon-based nanocages, the utilization of their unique porous structure and morphology for the construction of composites with foreign active species, and their significant applications to the advanced energy storage and conversion are reviewed. Structure–performance correlations are discussed in depth to highlight the contribution of carbon-based nanocages. The research challenges and trends are also envisaged for deepening and extending the study and application of this multifunctional material.     

钴-镍双金属磷化物中空纳米笼用于高效电解水

制备一种低成本、高效、稳定耐用的双功能电催化剂对于电催化水分解至关重要.本文采用自模板策略和原位磷化工艺相结合的方法构建了一种具有中空结构的钴镍双金属磷化物纳米笼(CoNiP_(x)).由于其独特的中空结构和钴镍双金属之间的协同效应,合成的CoNiP_(x)中空纳米笼催化剂在全pH值范围的电解质中对析氢反应均表现出优异...     

Direct observation of single-walled carbon nanotube growth at the atomistic scale

The growth dynamics of a single-walled carbon nanotube (SWNT) is observed in real-time using an in situ ultrahigh vacuum transmission electron microscope at 650 degrees C. SWNTs preferentially grow on smaller sized catalyst particles (diameter 相似文献   

Surface properties of nanosize hollow silica particles on the molecular level

Hollow particles are a newly developing material with the special properties of low density, thermal insulation and distinct optical activity. A number of preparation methods have been proposed in the literature. The polymer bead template method is one of the common processes to synthesize hollow particles, which can easily control particle size. However, byproducts produced during preparation adversely affect the natural environment. We have proposed an inorganic template method which overcomes the above disadvantages and also has some strong points. Although particle surface structure strongly affects wettability and particle dispersability, there are few reports that have discussed hollow particle structure. In this study, the shell wall structure of hollow particles was determined in detail by an analysis adsorption mechanism using the nitrogen adsorption isotherm. The results were compared with those of dense particles. The characteristics of the surface hydroxyl groups which react with surface modification reagents were then evaluated by water vapor adsorption. The modified surface was also characterized by Fourier-transform infrared spectroscopy and thermogravimetry/differential thermal analysis.     

Interactions of human endothelial cells with gold nanoparticles of different morphologies

The interactions between noncancerous, primary endothelial cells and gold nanoparticles with different morphologies but the same ligand capping are investigated. The endothelial cells are incubated with gold nanospheres, nanorods, hollow gold spheres, and core/shell silica/gold nanocrystals, which are coated with monocarboxy (1-mercaptoundec-11-yl) hexaethylene glycol (OEG). Cell viability studies show that all types of gold particles are noncytotoxic. The number of particles taken up by the cells is estimated using inductively coupled plasma (ICP), and are found to differ depending on particle morphology. The above results are discussed with respect to heating efficiency. Using experimental data reported earlier and theoretical model calculations which take into account the physical properties and distribution of particles in the cellular microenvironment, it is found that collective heating effects of several cells loaded with nanoparticles must be included to explain the observed viability of the endothelial cells.     

Micromechanics of seismic wave propagation in granular materials

In this study experimental data on a model soil in a cubical cell are compared with both discrete element (DEM) simulations and continuum analyses. The experiments and simulations used point source transmitters and receivers to evaluate the shear and compression wave velocities of the samples, from which some of the elastic moduli can be deduced. Complex responses to perturbations generated by the bender/extender piezoceramic elements in the experiments were compared to those found by the controlled movement of the particles in the DEM simulations. The generally satisfactory agreement between experimental observations and DEM simulations can be seen as a validation and support the use of DEM to investigate the influence of grain interaction on wave propagation. Frequency domain analyses that considered filtering of the higher frequency components of the inserted signal, the ratio of the input and received signals in the frequency domain and sample resonance provided useful insight into the system response. Frequency domain analysis and analytical continuum solutions for cube vibration show that the testing configuration excited some, but not all, of the system’s resonant frequencies. The particle scale data available from DEM enabled analysis of the energy dissipation during propagation of the wave. Frequency domain analysis at the particle scale revealed that the higher frequency content reduces with increasing distance from the point of excitation.     

Hollow thermoresponsive microgels

Thermoresponsive poly(N-isopropyl acrylamide) (pNIPAm) microgels possessing a hollow structure have been synthesized from core-shell nanoparticles upon oxidation of the particle core, followed by removal of the produced polymer segments by centrifugation. N,N'-(1,2-dihydroxyethylene)bisacrylamide (DHEA) is used as a cross-linker for preparing the degradable core, whereas N,N'-methylenebis(acrylamide) (BIS) is used as a cross-linker to add a nondegradable pNIPAm shell. Addition of NaIO(4) to a suspension of these particles in water leads to controlled degradation of the particle core by cleavage of the 1,2-glycol bond in DHEA. Fluorescence spectroscopy, UV/Vis spectroscopy, and photon correlation spectroscopy are used to characterize the hollow particles produced.