Gold Nanoparticle Internal Structure and Symmetry Probed by Unified Small-Angle X-ray Scattering and X-ray Diffraction Coupled with Molecular Dynamics Analysis

Toward Distinguishing between the Superchaotropic and Hydrophobic Characters of Nanometric-Sized Ions in Interaction with PEGylated Surfaces

In this study, we explore the superchaotropic effect of various polyoxometalate or boron cluster nano-ions on hydrophilic neutral surfaces. Nano-ions, characterized by low charge densities, exhibit strong adsorption on non-ionic hydrophilic surfaces like PEGylated micelles. This adsorption phenomenon was attributed to the enthalpically favorable dehydration of nano-ions, the so-called superchaotropic effect. Here, we investigate the adsorption of three nano-ions, α-SiW12O404-, α-PW12O403-, and B12I122-, with decreasing charge density or increasing superchaotropicity (or hydrophobicity), on hydrophilic solid surfaces, PEGylated gold nanoparticles, and PEGylated gold-coated quartz crystal. Solid surfaces are devoid of hydrophobic regions, enabling the study of the subtle nuance between hydrophobic and superchaotropic effects. Unlike adsorption on PEGylated micelles, the adsorption constant decreases with a reduced charge density, aligning with the well-established principle that hydrophobic ions do not adsorb on hydrophilic surfaces. This research improves our understanding of the subtle difference between superchaotropic and hydrophobic effects in nano-ion adsorption phenomena.

Type-I CdS/ZnS Core/Shell Quantum Dot-Gold Heterostructural Nanocrystals for Enhanced Photocatalytic Hydrogen Generation

Developing Type-I core/shell quantum dots is of great importance toward fabricating stable and sustainable photocatalysts. However, the application of Type-I systems has been limited due to the strongly confined photogenerated charges by the energy barrier originating from the wide-bandgap shell material. In this project, we found that through the decoration of Au satellite-type domains on the surface of Type-I CdS/ZnS core/shell quantum dots, such an energy barrier can be effectively overcome and an over 400-fold enhancement of photocatalytic H2 evolution rate was achieved compared to bare CdS/ZnS quantum dots. Transient absorption spectroscopic studies indicated that the charges can be effectively extracted and subsequently transferred to surrounding molecular substrates in a subpicosecond time scale in such hybrid nanocrystals. Based on density functional theory calculations, the ultrafast charge separation rates were ascribed to the formation of intermediate Au2S layer at the semiconductor-metal interface, which can successfully offset the energy confinement introduced by the ZnS shell. Our findings not only provide insightful understandings on charge carrier dynamics in semiconductor-metal heterostructural materials but also pave the way for the future design of quantum dot-based hybrid photocatalytic systems.

Size-dependent theoretical and experimental photothermal conversion efficiency of spherical gold nanoparticles

INTRODUCTION

Due to their biocompatible and plasmonic properties, gold nanoparticles (Au NPs) are good candidates to be photosensitizers in photothermal cancer therapy (PTT).

MATERIALS AND METHODS

In this paper, the dependence of the NIR-light-to-heat energy on Au NPs size was investigated. Moreover, to determine the photosensitizing properties of gold nanoparticles, PTT was conducted on two colon cell lines: SW480 and SW620 by irradiating them with two lasers having different wavelengths.

RESULTS

Transmission electron microscopy showed that the respective sizes of Au NPs were 10 nm, 12 nm and 16 nm. Moreover, local as well as global structural measurements showed that all synthesized Au NPs were crystalline and UV-Vis spectroscopy revealed that with increasing nanoparticles size the position of the surface Plasmon resonance (SPR) peaks is shifted to higher wavelengths. Decrease of cells viability was observed, when they were cultured with Au NPs and irradiated by 650 nm and 808 nm lasers. Moreover, FTIR and Raman spectra of cells, showed structural changes in DNA, phospholipids, proteins and cholesterol caused by the addition of nanoparticles and laser irradiation. The chemical changes were more pronounced in the cells cultured with Au NPs and irradiated by 650 nm lasers and these changes were dependent on the nanoparticle size. Moreover, the viability of cells investigated by the MTS assay showed, that the percentage of dead cells (∼40%) is the highest for cells cultured with 8 nm Au NPs and irradiated by the 650 nm laser. The photothermal conversion efficiency calculated from the experimental results showed a decrease of this parameter from 70% to 55% and from 61% to 48% with increasing particle size, for 650 nm and 808 nm lasers, respectively.

CONCLUSIONS

The obtained results showed that the photothermal conversion efficiency of Au NPs is size-tunable, and can be correlated with the absorption/extinction ratios calculated by the Mie theory.

Precise size control of hydrophobic gold nanoparticles in the 2-5 nm range

We report a seed-mediated synthesis strategy to control the size of gold nanoparticles at the atomic scale in the 2-5 nm size range. Starting from 2 nm seeds, a regrowth in organic solvent with a designed amount of precursor can achieve in a predictive fashion a precise mean size with a 0.3 nm resolution. We show that these monodisperse nanoparticles assemble into a 2D hexagonal lattice over a distance that can span tens of micrometers.

Combined Small-Angle Neutron Scattering/Small-Angle X-ray Scattering Analysis for the Characterization of Silver Nanoparticles Prepared via Photoreduction in Water-in-Oil Microemulsions

In this study, we used small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) to investigate the formation process of silver (Ag) nanoparticles (NPs) in water-in-oil (w/o) reverse microemulsions comprising sodium bis(2-ethylhexyl) sulfosuccinate (AOT), water, and organic solvents (such as benzene, octane, and decane) by the photoreduction of silver perchlorate (AgClO₄). Combining SANS and SAXS, the structural changes in the w/o microemulsions before and after the formation of Ag NPs via photoreduction were quantitatively evaluated. From the SANS experiments performed using the contrast-variation method, the size of water cores containing Ag NPs and the thickness of the AOT shells were calculated using the core-shell hard-sphere model. The size of the Ag NPs and their aggregates was calculated via SAXS analysis based on the polydisperse sphere model with a Schulz-Zimm distribution. We found that aggregates of three or four primary Ag NPs are formed by, first, the aggregation of water droplets through the entanglement of the tails of the AOT shell, followed by the self-assembly of Ag NPs into their aggregates because of particle-particle attractive interactions.

Facile synthesis of gold-silver/copper sulfide nanoparticles for the selective/sensitive detection of chromium, photochemical and bactericidal application

In this project, bimetallic Au-Agnanoparticles/CuS nanoparticles were prepared via simple hydrothermal methods, which were used as highly efficient material for Cr (III) detection, photocatalytic, and biological process. The Au-Ag/CuS nanoparticles was studied via UV-visible spectroscopy, field-emission scanning electron microscopy, Dynamic light scattering, and X-ray diffraction. The zeta potential and effective size of Au-Ag/CuS nanoparticles was -32.1 mV and 25 nm respectively. The response time of Cr (III) ions interaction was 2 min. The lowest detection of Cr (III) by Au-Ag/CuS nanoparticles was 0.5 nM. The Au-Ag/CuS nano catalyst was applied to decomposition of drug under visible lamp irradiation. The photo degradation response of drug was 100.0% in 30 min irradiation. The particles exhibited excellent antibacterial activities.

Mixed-monolayer functionalized gold nanoparticles for cancer treatment: Atomistic molecular dynamics simulations study

Gold nanoparticles (AuNPs) are employed as drug carriers due to their inertness, non-toxicity, and ease of synthesis. An experimental search for the optimal AuNP design would require a systematic variation of physico-chemical properties which is time-consuming and expensive. Computational methods provide quicker and cheaper approach to complement experiments and provide useful guidelines. In this paper, we performed atomistic molecular dynamics simulations to study how the size, hydrophobicity, and concentration of the drug affect the structure of functionalized AuNPs in the aqueous environment. We simulated two groups of nano-systems functionalized with a zwitterionic background ligand, and a ligand carrying a drug (Quinolinol or Panobinostat). Results indicate that in the case of a hydrophobic drug (Quinolinol), the hydrophobicity drives the conformation changes of the coating layer. The tendency of the hydrophobic drug to reduce its solvent-accessible surface results in a decrease of the coating thickness and the overall NP size. Although the amount of accessible drug can be increased by increasing its initial concentration, it will compromise the solubility of the system. In the case of a hydrophilic drug (Panobinostat), the ligand in excess has a dominant influence on the final structure of the coating conformations. The percentage of accessible drug is significantly higher than in the hydrophobic systems for any given ratio. It implies that for hydrophilic systems we can generally expect higher biological efficiency. Our results highlight the importance of taking into account physico-chemical properties of drugs and ligands when developing gold-based nanosystems, especially in the case of hydrophobic drugs.

Statistical Characterization of the Morphologies of Nanoparticles through Machine Learning Based Electron Microscopy Image Analysis

Although transmission electron microscopy (TEM) may be one of the most efficient techniques available for studying the morphological characteristics of nanoparticles, analyzing them quantitatively in a statistical manner is exceedingly difficult. Herein, we report a method for mass-throughput analysis of the morphologies of nanoparticles by applying a genetic algorithm to an image analysis technique. The proposed method enables the analysis of over 150,000 nanoparticles with a high precision of 99.75% and a low false discovery rate of 0.25%. Furthermore, we clustered nanoparticles with similar morphological shapes into several groups for diverse statistical analyses. We determined that at least 1,500 nanoparticles are necessary to represent the total population of nanoparticles at a 95% credible interval. In addition, the number of TEM measurements and the average number of nanoparticles in each TEM image should be considered to ensure a satisfactory representation of nanoparticles using TEM images. Moreover, the statistical distribution of polydisperse nanoparticles plays a key role in accurately estimating their optical properties. We expect this method to become a powerful tool and aid in expanding nanoparticle-related research into the statistical domain for use in big data analysis.

Antibacterial and Immunomodulatory Potentials of Biosynthesized Ag, Au, Ag-Au Bimetallic Alloy Nanoparticles Using the Asparagus racemosus Root Extract

Two noble metals, such as silver and gold alloy nanoparticles, were successfully synthesized by the microwave assisted method in the presence of the Asparagus racemosus root extract and were used as an antibacterial and immunomodulatory agent. The nanostuctures of the synthesized nanoparticles were confirmed by various spectroscopic and microscopic techniques. The UV-vis spectrum exhibits a distinct absorption peak at 483 nm for the bimetallic alloy nanoparticles. The microscopic analysis revealed the spherical shaped morphology of the biosynthesized nanoparticles with a particle size of 10-50 nm. The antibacterial potential of the green synthesized single metal (AgNPs and AuNPs) and bimetallic alloy nanoparticles was tested against five bacterial strains. The bimetallic alloy nanoparticles displayed the highest zone of inhibition against P. aeurgnosia and S.aureus strains when compared to single metal nanoparticles and plant extract. In addition, the inmmunomodulatory potential of the root extract of A. racemosus, AgNPs, AuNPs, and Ag-Au alloy NPs is achieved by measuring the cytokine levels in macrophages (IL-1β, IL-6, and TNF-α) and NK cells (IFN-γ) of NK92 and THP1 cells using the solid phase sandwich ELISA technique. The results showed that the root extract of A. racemosus, AgNPs, and AuNPs can reduce the pro-inflammatory cytokine levels in the macrophages cells, while Ag-Au alloy NPs can reduce cytokine responses in NK92 cells. Overall, this study shows that the microwave assisted biogenic synthesized bimetallic nanoalloy nanoparticles could be further explored for the development of antibacterial and anti-inflammatory therapies.

Colloidal assembly in droplets: structures and optical properties

Colloidal assembly in emulsion drops provides fundamental tools for studying optimum particle arrangement under spherical confinement and practical means for producing photonic microparticles. Recent progress has revealed that energetically favored cluster configurations are different from conventional supraballs, which could enhance optical performance. This paper reviews state-of-the-art emulsion-templated colloidal clusters, and particularly focuses on recently reported novel structures such as icosahedral, decahedral, and single-crystalline face-centered cubic (fcc) clusters. We classify the clusters according to the number of component particles as small (N < O(10²)), medium (O(10²) ≤N≤O(10⁴)), and large (N≥O(10⁵)). For each size of clusters, we discuss the detailed structures, mechanisms of cluster formation, and optical properties and potential applications. Finally, we outline current challenges and questions that require further investigation.

A pressure-actuated flow cell for soft X-ray spectromicroscopy in liquid media

We present and fully characterize a flow cell dedicated to imaging in liquid at the nanoscale. Its use as a routine sample environment for soft X-ray spectromicroscopy is demonstrated, in particular through the spectral analysis of inorganic particles in water. The care taken in delineating the fluidic pathways and the precision associated with pressure actuation ensure the efficiency of fluid renewal under the beam, which in turn guarantees a successful utilization of this microfluidic tool for in situ kinetic studies. The assembly of the described flow cell necessitates no sophisticated microfabrication and can be easily implemented in any laboratory. Furthermore, the design principles we relied on are transposable to all microscopies involving strongly absorbed radiation (e.g. X-ray, electron), as well as to all kinds of X-ray diffraction/scattering techniques.

Toward a Chemical Control of Colloidal YVO4 Nanoparticles Microstructure

Rare-earth-doped oxides are a class of compounds that have been largely studied in the context of the development of luminescent nanocrystals for various applications including fluorescent labels for bioimaging, MRI contrast agents, luminescent nanocomposite coatings, etc. Elaboration of colloidal suspensions is usually achieved through coprecipitation. Particles exhibit emission properties that are similar to the bulk counterparts, although altered by crystalline defects or surface quenching species. Focusing on YVO₄:Eu, one of the first reported systems, the aim of this work is to revisit the elaboration of nanoparticles obtained through a simple aqueous coprecipitation route. The objective is more precisely to get a better understanding of the parameters affecting the particles' internal microstructure, a feature that is poorly controlled and characterized. We show that the hydroxyl concentration in the precursor solution has a drastic effect on the particles' microstructure. Moreover, discrepancies in the reported particle structure are shown to possibly arise from the carbonation of the strongly basic orthovanadate precursor. For this study, SAXS/WAXS is shown to be a powerful tool to characterize the multiscale structure of the particles. It could be shown that playing on the precursor composition, it may be varied between almost monocrystalline nanocrystals to particles exhibiting a hierarchical microstructure well described by a surface fractal model. This work provides a new methodology for the characterization of nanoparticles microstructure and opens new directions for its optimization in view of applications.

The transformation of cuboctahedral to icosahedral nanoparticles: atomic structure and dynamics

The rearrangement of transition metal nanoparticles from cuboctahedral to icosahedral structures is studied for up to 923 atoms. The atomic structure and temperature dependence of the transition are investigated with a well-defined collective variable. This collective variable describes the folding of the square fcc(100) facets into two triangular facets through a linear combination of the diagonals of all fcc(100) facets of all shells of the particle. Activation barriers are determined through harmonic transition state theory and constrained molecular dynamics simulations based on force field potentials. These calculations predict an activation entropy larger than 1 meV K^-1, leading to strongly temperature dependent activation barriers. Density functional theory calculations were additionally performed both as single point calculations and as full optimizations. Cu, Ag, Au and Ni clusters show low barriers for concerted, symmetric transition up to the 309-atomic clusters. In contrast, for Pd, Pt, Rh and Ir higher barriers are required, already for the 147-atomic clusters. With increasing barriers, an asymmetric but still concerted rearrangement becomes energetically more favorable than the fully symmetric transformation. The material-dependence of the transition can be correlated with the melting point of the bulk metals.

Cluster-mining: an approach for determining core structures of metallic nanoparticles from atomic pair distribution function data

A novel approach for finding and evaluating structural models of small metallic nanoparticles is presented. Rather than fitting a single model with many degrees of freedom, libraries of clusters from multiple structural motifs are built algorithmically and individually refined against experimental pair distribution functions. Each cluster fit is highly constrained. The approach, called cluster-mining, returns all candidate structure models that are consistent with the data as measured by a goodness of fit. It is highly automated, easy to use, and yields models that are more physically realistic and result in better agreement to the data than models based on cubic close-packed crystallographic cores, often reported in the literature for metallic nanoparticles.

Multifunctionality of gold nanoparticles: Plausible and convincing properties

In a couple of decades, nanotechnology has become a trending area in science due to it covers all subject that combines diverse range of fields including but not limited to chemistry, physics and medicine. Various metal and metal oxide nanomaterials have been developed for wide range applications. However, the application of gold nanostructures and nanoparticles has been received more attention in various biomedical applications. The unique property of gold nanoparticles (AuNPs) is surface plasmon resonance (SPR) that determine the size, shape and stability. The wide surface area of AuNPs eases the proteins, peptides, oligonucleotides, and many other compounds to tether and enhance the biological activity of AuNPs. AuNPs have multifunctionality including antimicrobial, anticancer, drug and gene delivery, sensing applications and imaging. This state-of-the-art review is focused on the role of unique properties of AuNPs in multifunctionality and its various applications.

Designed Two- and Three-Dimensional Protein Nanocage Networks Driven by Hydrophobic Interactions Contributed by Amyloidogenic Motifs

Precise manipulation of protein self-assembly by noncovalent interactions into programmed networks to mimic naturally occurring nanoarchitectures in living organisms is a challenge due to its structural heterogeneity, flexibility, and complexity. Herein, by taking advantage of both the hydrophobic forces contributed by the "GLMVG" motif, a kind of amyloidogenic motif (AM), and the high symmetry of protein nanocages, we have built an effective protein self-assembly strategy for the construction of two-dimensional (2D) or three-dimensional (3D) protein nanocage arrays. According to this strategy, "GLMVG" AMs from β-amyloid 42 were grafted onto the outer surface of a 24-mer ferritin nanocage close to its C₄ symmetry channels, initially resulting in the production of subgrade 2D nanocage arrays and ultimately generating 3D highly ordered arrays with a simple cubic packing pattern as the reaction time increases. More importantly, the reversibility and the formation rate of these protein arrays can be modulated by pH. This work provides a de novo design strategy for accurate control over 2D or 3D protein self-assemblies.

Structural properties of sub-nanometer metallic clusters

At the nanoscale, the investigation of structural features becomes fundamental as we can establish relationships between cluster geometries and their physicochemical properties. The peculiarity lies in the variety of shapes often unusual and far from any geometrical and crystallographic intuition clusters can assume. In this respect, we should treat and consider nanoparticles as a new form of matter. Nanoparticle structures depend on their size, chemical composition, ordering, as well as external conditions e.g. synthesis method, pressure, temperature, support. On top of that, at finite temperatures nanoparticles can fluctuate among different structures, opening new and exciting horizons for the design of optimal nanoparticles for advanced applications. This article aims to overview geometrical features of transition metal clusters and of their various rearrangements.

Enhanced catalytic and SERS performance of shape/size controlled anisotropic gold nanostructures

Au nanostars of different sizes and shapes prepared using a simple method and their applications.

Size-Dependent Fault-Driven Relaxation and Faceting in Zincblende CdSe Colloidal Quantum Dots

Surface chemistry and core defects are known to play a prominent role in governing the photophysical properties of nanocrystalline semiconductors. Nevertheless, investigating them in small nanocrystals remains a complex task. Here, by combining X-ray scattering techniques in the wide- and small-angle regions and using the Debye scattering equation (DSE) method of analysis, we unveil a high density of planar defects in oleate-terminated zincblende (ZB) CdSe colloidal quantum dots (QDs) and size-dependent faceting within a square-cuboid morphology. Atomistic models of faulted ZB nanocrystals, based on the probabilistic stacking of CdSe layers in cubic and hexagonal sequences, and data analysis point to the preferential location of faults near the center of nanocrystals. By finely modeling faulting and morphological effects on the X-ray scattering pattern, a relaxation of the Cd-Se bond distance parallel to the stacking direction, up to +3% (2.71 Å) with respect to the reference bulk value (2.63 Å), is detected, at the cubic/hexagonal transitions. The smallest nanocrystals show cubic {100} facets; {111} facets appear above 4 nm and progressively extend at larger sizes. These structural and morphological features likely vary depending on the synthesis conditions; nevertheless, since planar defects are nearly ubiquitous in CdSe QDs, the modeling approach here presented has a general validity. This work also points to the great potential of combining small- and wide-angle X-ray scattering and DSE-modeling techniques in gaining important knowledge on atomic-scale defects of semiconductor nanocrystals, underpinning the comprehension of the impact of structural defectiveness on the exciting properties of these QDs.

A Review of Ghost Imaging via Sparsity Constraints

Different from conventional imaging methods, which are based on the first-order field correlation, ghost imaging (GI) obtains the image information through high-order mutual-correlation of light fields from two paths with an object appearing in only one path. As a new optical imaging technology, GI not only provides us new capabilities beyond the conventional imaging methods, but also gives out a new viewpoint of imaging physical mechanism. It may be applied to many potential applications, such as remote sensing, snap-shot spectral imaging, thermal X-ray diffraction imaging and imaging through scattering media. In this paper, we reviewed mainly our research work of ghost imaging via sparsity constraints (GISC) and discussed the application and theory prospect of GISC concisely.

Gold nanocrystal labels provide a sequence-to-3D structure map in SAXS reconstructions

Small-angle x-ray scattering (SAXS) is a powerful technique to probe the structure of biological macromolecules and their complexes under virtually arbitrary solution conditions, without the need for crystallization. While it is possible to reconstruct molecular shapes from SAXS data ab initio, the resulting electron density maps have a resolution of ~1 nm and are often insufficient to reliably assign secondary structure elements or domains. We show that SAXS data of gold-labeled samples significantly enhance the information content of SAXS measurements, allowing the unambiguous assignment of macromolecular sequence motifs to specific locations within a SAXS structure. We first demonstrate our approach for site-specifically internally and end-labeled DNA and an RNA motif. In addition, we present a protocol for highly uniform and site-specific labeling of proteins with small (~1.4 nm diameter) gold particles and apply our method to the signaling protein calmodulin. In all cases, the position of the small gold probes can be reliably identified in low-resolution electron density maps. Enhancing low-resolution measurements by site-selective gold labeling provides an attractive approach to aid modeling of a large range of macromolecular systems.

Beyond Magic Numbers: Atomic Scale Equilibrium Nanoparticle Shapes for Any Size

In the pursuit of complete control over morphology in nanoparticle synthesis, knowledge of the thermodynamic equilibrium shapes is a key ingredient. While approaches exist to determine the equilibrium shape in the large size limit (≳10-20 nm) as well as for very small particles (≲2 nm), the experimentally increasingly important intermediate size regime has largely remained elusive. Here, we present an algorithm, based on atomistic simulations in a constrained thermodynamic ensemble, that efficiently predicts equilibrium shapes for any number of atoms in the range from a few tens to many thousands of atoms. We apply the algorithm to Cu, Ag, Au, and Pd particles with diameters between approximately 1 and 7 nm and reveal an energy landscape that is more intricate than previously suggested. The thus obtained particle type distributions demonstrate that the transition from icosahedral particles to decahedral and further into truncated octahedral particles occurs only very gradually, which has implications for the interpretation of experimental data. The approach presented here is extensible to alloys and can in principle also be adapted to represent different chemical environments.

SLADS: a parallel code for direct simulations of scattering of large anisotropic dense nanoparticle systems

SLADS(http://www.pims.ac.cn/Resources.html), a parallel code for direct simulations of X-ray scattering of large anisotropic dense nanoparticle systems of arbitrary species and atomic configurations, is presented. Particles can be of arbitrary shapes and dispersities, and interactions between particles are considered. Parallelization is achieved in real space for the sake of memory limitation. The system sizes attempted are up to one billion atoms, and particle concentrations in dense systems up to 0.36. Anisotropy is explored in terms of superlattices. One- and two-dimensional small-angle scattering or diffraction patterns are obtained.SLADSis validated self-consistently or against cases with analytical solutions.

Size-tunable uniform gold octahedra: fast synthesis, characterization, and plasmonic properties

Well-defined octahedral Au nanocrystals were facilely and precisely prepared in high yield by modified polyol process.

Fourier-Transform Ghost Imaging with Hard X Rays

Knowledge gained through x-ray crystallography fostered structural determination of materials and greatly facilitated the development of modern science and technology in the past century. However, it is only applied to crystalline structures and cannot resolve noncrystalline materials. Here we demonstrate a novel lensless Fourier-transform ghost imaging method with pseudothermal hard x rays that extends x-ray crystallography to noncrystalline samples. By measuring the second-order intensity correlation function of the light, Fourier-transform diffraction pattern of a complex amplitude sample is achieved at the Fresnel region in our experiment and the amplitude and phase distributions of the sample in the spatial domain are retrieved successfully. For the first time, ghost imaging is experimentally realized with x rays. Since a highly coherent x-ray source is not required, the method can be implemented with laboratory x-ray sources and it also provides a potential solution for lensless diffraction imaging with fermions, such as neutrons and electrons where intensive coherent sources usually are not available.

MOMAC: a SAXS/WAXS laboratory instrument dedicated to nanomaterials

This article presents the technical characteristics of a newly built small- and wide-angle X-ray scattering (SAXS/WAXS) apparatus dedicated to structural characterization of a wide range of nanomaterials in the powder or dispersion form. The instrument is based on a high-flux rotating anode generator with a molybdenum target, enabling the assessment of highly absorbing samples containing heavy elements. The SAXS part is composed of a collimation system including a multilayer optic and scatterless slits, a motorized sample holder, a vacuum chamber, and a two-dimensional image-plate detector. All the control command is done through a TANGO interface. Normalization and data correction yield scattering patterns at the absolute scale automatically with a q range from 0.03 to 3.2 Å−1. The WAXS part features a multilayer collimating optic and a two-dimensional image-plate detector with variable sample-to-detector distances. The accessible q range is 0.4–9 Å−1, ensuring a large overlap in q range between the two instruments. A few examples of applications are also presented, namely coupled SAXS/WAXS structure and symmetry determination of gold nanocrystals in solution and characterization of imogolite nanotubes and iron-filled carbon nanotube samples.

A facile and green strategy for the synthesis of Au, Ag and Au-Ag alloy nanoparticles using aerial parts of R. hypocrateriformis extract and their biological evaluation

A facile and green strategy is reported here to synthesize gold (Au), silver (Ag) and gold-silver (Au-Ag) alloy nanoparticles (NPs) through bio-reduction reactions of aqueous corresponding metal precursors mediated by extracts of aerial parts of R. hypocrateriformis, which act as both reducing and stabilizing agents, under microwave irradiation. UV-vis spectrophotometer, XRD, FT-IR, FESEM/TEM, TGA and EDAX analysis were used to characterize the obtained NPs. The formation of NPs is evident from their surface plasmon resonance peak observed at λ_max=∼550, 450 and 500nm for Au, Ag and Au-Ag alloy NPs respectively. XRD pattern revealed that fcc structure, while FT-IR spectra signify the presence of phytochemicals adsorbed on NPs. Such a biofunctionalized NPs were characterized by their weight loss, 30% due to thermal degradation of plant phytochemicals observed in TG analysis. The spherical shape of Au, Ag and Au-Ag alloy NPs (∼10-50nm) is observed by FE-SEM/TEM images. EDAX analysis confirms the expected elemental composition. Moreover, these NPs showed enhanced antimicrobial, antioxidant, and anticancer activities, though it is more pronounced for Au-Ag alloy NPs, which is due to the combining effect of phytochemicals, Au and Ag metals. Thus, the biosynthesized NPs could be applied as effective growth inhibitors for various biomedical applications.

Small Angle X-ray Scattering for Nanoparticle Research

X-ray scattering is a structural characterization tool that has impacted diverse fields of study. It is unique in its ability to examine materials in real time and under realistic sample environments, enabling researchers to understand morphology at nanometer and angstrom length scales using complementary small and wide angle X-ray scattering (SAXS, WAXS), respectively. Herein, we focus on the use of SAXS to examine nanoscale particulate systems. We provide a theoretical foundation for X-ray scattering, considering both form factor and structure factor, as well as the use of correlation functions, which may be used to determine a particle's size, size distribution, shape, and organization into hierarchical structures. The theory is expanded upon with contemporary use cases. Both transmission and reflection (grazing incidence) geometries are addressed, as well as the combination of SAXS with other X-ray and non-X-ray characterization tools. We conclude with an examination of several key areas of research where X-ray scattering has played a pivotal role, including in situ nanoparticle synthesis, nanoparticle assembly, and operando studies of catalysts and energy storage materials. Throughout this review we highlight the unique capabilities of X-ray scattering for structural characterization of materials in their native environment.