Nanoparticle size distribution quantification: results of a small-angle X-ray scattering inter-laboratory comparison

Synthesis and Characterization of Ultra-Small Gold Nanoparticles in the Ionic Liquid 1-Ethyl-3-methylimidazolium Dicyanamide, [Emim][DCA]

We report on gold clusters with around 62 gold atoms and a diameter of 1.15±0.10 nm. Dispersions of the clusters are long-term stable for two years at ambient conditions. The synthesis was performed by mixing tetrachloroauric acid (HAuCl4  ⋅ 3 H2 O) with the ionic liquid 1-ethyl-3-methylimidazolium dicyanamide ([Emim][DCA]) at temperatures of 20 to 80 °C. Characterization was performed with small-angle X-ray scattering (SAXS), UV-Vis spectroscopy, and MALDI-TOF mass spectrometry. A three-stage model is proposed for the formation of the clusters, in which cluster growth from gold nuclei takes place according to the Lifshitz-Slyozov-Wagner (LSW) model followed by oriented attachment to form colloidal stable clusters.

Retrieving the size distribution of SBA-15 mesopores from small-angle X-ray scattering data using a Monte Carlo method

A Monte Carlo (MC) method was introduced into a state-of-the-art model used to analyse small-angle X-ray scattering (SAXS) data of SBA-15, an ordered mesoporous material with many applications. With this new procedure, referred to herein as the SBA-15+MC model, it is possible to retrieve the size distribution of the mesopores, D(r), in a free modelling approach. To achieve this, two main points were addressed: (i) based on previous implementations, the method was adapted to work with long core-shell cylinders; (ii) since the MC model requires longer processing times, strategies to speed up the calculations were developed, which included a simplified version of the original model used to analyse SAXS data of SBA-15 (referred to as the SBA-15 model) as well as the determination of several structural features from the SAXS curve prior to the fit. The new model was validated with simulated data and later used to fit experimental SAXS curves of SBA-15. The obtained results show that the SBA-15 model only works well because the mesopore size distribution of SBA-15 is narrow, whereas the new approach can be successfully used in cases where D(r) is wider and/or has a more complex profile, such as SBA-15 with expanded mesopores. Even though a specific SAXS example was chosen to prove the model, the strategies presented herein are general and suitable for inclusion in other models aimed at the analysis of SBA-15 and similar ordered mesoporous materials.

Iron Oxide Nanocubes as a New Certified Reference Material for Nanoparticle Size Measurements

The rational design and increasing industrial use of nanomaterials require a reliable characterization of their physicochemical key properties like size, size distribution, shape, and surface chemistry. This calls for nanoscale reference materials (nanoRMs) for the validation and standardization of commonly used characterization methods closely matching real-world nonspherical nano-objects. This encouraged us to develop a nonspherical nanoRM of very small size consisting of 8 nm iron oxide nanocubes (BAM-N012) to complement spherical gold, silica, and polymer nanoRMs. In the following, the development and production of this nanoRM are highlighted including the characterization by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) as complementary methods for size and shape parameters, homogeneity and stability studies, and calculation of a complete uncertainty budget of the size features. The determination of the nanocubes' edge length by TEM and SAXS allows a method comparison. In addition, SAXS measurements can also provide the mean particle number density and the mass concentration. The certified size parameters, area equivalent circular diameter and square edge length, determined by TEM with a relative expanded uncertainty below 9%, are metrologically traceable to a natural constant for length, the very precisely known (111) lattice spacing of silicon. Cubic BAM-N012 qualifies as a certified nanoRM for estimating the precision and trueness, validation, and quality assurance of particle size and shape measurements with electron microscopy and SAXS as well as other sizing methods suitable for nanomaterials. The production of this new iron oxide nanocube RM presents an important achievement for the nanomaterial community, nanomaterial manufacturers, and regulators.

X-ray scattering as an effective tool for characterizing liquid metal composite morphology

Quantitative analysis of particle size and size distribution is crucial in establishing structure-property relationships of composite materials. An emerging soft composite architecture involves dispersing droplets of liquid metal throughout an elastomer, enabling synergistic properties of metals and soft polymers. The structure of these materials is typically characterized through real-space microscopy and image analysis; however, these techniques rely on magnified images that may not represent the global-averaged size and distribution of the droplets. In this study, we utilize ultra-small angle X-ray scattering (USAXS) as a reciprocal-space characterization technique that yields global-averaged dimensions of eutectic gallium indium (EGaIn) alloy soft composites. The Unified fit and Monte Carlo scattering methods are applied to determine the particle size and size distributions of the liquid metal droplets in the composites and are shown to be in excellent agreement with results from real-space image analysis. Additionally, all methods indicate that the droplets are getting larger as they are introduced into composites, suggesting that the droplets are agglomerating or possibly coalescing during dispersion. This work demonstrates the viability of X-ray scattering to elucidate structural information about liquid metal droplets for material development for applications in soft robotics, soft electronics, and multifunctional materials.

Size characterization of nanomaterials in environmental and biological matrices through non-electron microscopic techniques

Engineered nanomaterials (ENs) can enter the environment, and accumulate in food chains, thereby causing environmental and health problems. Size characterization of ENs is critical for further evaluating the interactions among ENs in biological and ecological systems. Although electron microscope is a powerful tool in obtaining the size information, it has limitations when studying nanomaterials in complex matrices. In this review, we summarized non-electron microscope-based techniques, including chromatography-based, mass spectrometry-based, synchrotron radiation- and neutron-based techniques for detecting the size of ENs in environmental and biological matrices. The advantages and disadvantages of these techniques were highlighted. The perspectives on size characterization of ENs in complex matrices were also presented.

Towards automation of the polyol process for the synthesis of silver nanoparticles

Metal nanoparticles have a substantial impact across different fields of science, such as photochemistry, energy conversion, and medicine. Among the commonly used nanoparticles, silver nanoparticles are of special interest due to their antibacterial properties and applications in sensing and catalysis. However, many of the methods used to synthesize silver nanoparticles often do not result in well-defined products, the main obstacles being high polydispersity or a lack of particle size tunability. We describe an automated approach to on-demand synthesis of adjustable particles with mean radii of 3 and 5 nm using the polyol route. The polyol process is a promising route for silver nanoparticles e.g., to be used as reference materials. We characterised the as-synthesized nanoparticles using small-angle X-ray scattering, dynamic light scattering and further methods, showing that automated synthesis can yield colloids with reproducible and tuneable properties.

Kinetic Processes in Enzymatic Nanoreactors for In Vivo Detoxification

Enzymatic nanoreactors are enzyme-encapsulated nanobodies that are capable of performing biosynthetic or catabolic reactions. For this paper, we focused on therapeutic enzyme nanoreactors for the neutralization of toxicants, paying special attention to the inactivation of organophosphorus compounds (OP). Therapeutic enzymes that are capable of detoxifying OPs are known as bioscavengers. The encapsulation of injectable bioscavengers by nanoparticles was first used to prevent fast clearance and the immune response to heterologous enzymes. The aim of enzyme nanoreactors is also to provide a high concentration of the reactive enzyme in stable nanocontainers. Under these conditions, the detoxification reaction takes place inside the compartment, where the enzyme concentration is much higher than in the toxicant diffusing across the nanoreactor membrane. Thus, the determination of the concentration of the encapsulated enzyme is an important issue in nanoreactor biotechnology. The implications of second-order reaction conditions, the nanoreactor’s permeability in terms of substrates, and the reaction products and their possible osmotic, viscosity, and crowding effects are also examined.

Versailles project on advanced materials and standards (VAMAS) interlaboratory study on measuring the number concentration of colloidal gold nanoparticles

We describe the outcome of a large international interlaboratory study of the measurement of particle number concentration of colloidal nanoparticles, project 10 of the technical working area 34, "Nanoparticle Populations" of the Versailles Project on Advanced Materials and Standards (VAMAS). A total of 50 laboratories delivered results for the number concentration of 30 nm gold colloidal nanoparticles measured using particle tracking analysis (PTA), single particle inductively coupled plasma mass spectrometry (spICP-MS), ultraviolet-visible (UV-Vis) light spectroscopy, centrifugal liquid sedimentation (CLS) and small angle X-ray scattering (SAXS). The study provides quantitative data to evaluate the repeatability of these methods and their reproducibility in the measurement of number concentration of model nanoparticle systems following a common measurement protocol. We find that the population-averaging methods of SAXS, CLS and UV-Vis have high measurement repeatability and reproducibility, with between-labs variability of 2.6%, 11% and 1.4% respectively. However, results may be significantly biased for reasons including inaccurate material properties whose values are used to compute the number concentration. Particle-counting method results are less reproducibile than population-averaging methods, with measured between-labs variability of 68% and 46% for PTA and spICP-MS respectively. This study provides the stakeholder community with important comparative data to underpin measurement reproducibility and method validation for number concentration of nanoparticles.

General Expression for the Size-Dependent Optical Properties of Quantum Dots

While initial theories on quantum confinement in colloidal quantum dots (QDs) led to analytical band gap/size relations or sizing functions, numerical methods describe size quantization more accurately. However, because of the lack of reliable sizing functions, researchers fit experimental band gap/size data sets using models with redundant, physically meaningless parameters that break down upon extrapolation. Here, we propose a new sizing function based on a proportional correction for nonparabolic bands. Using known bulk parameters, we predict size quantization for groups IV, III-V, II-VI, and IV-VI and metal-halide perovskite semiconductors, including straightforward adaptations for negative-gap semiconductors and nonspherical QDs. Refinement with respect to experimental data is possible using the Bohr diameter as a fitting parameter, by which we show a statistically relevant difference in the band gap/size relation for wurtzite and zinc blende CdSe. The general sizing function proposed here unifies the QD size calibration and enables researchers to assess bulk semiconductor parameters and predict the size quantization in unexplored materials.

Pyroelectric Nanogenerator Based on an SbSI-TiO2 Nanocomposite

For the first time, a composite of ferroelectric antimony sulfoiodide (SbSI) nanowires and non-ferroelectric titanium dioxide (TiO₂) nanoparticles was applied as a pyroelectric nanogenerator. SbSI nanowires were fabricated under ultrasonic treatment. Sonochemical synthesis was performed in the presence of TiO₂ nanoparticles. The mean lateral dimension d_a = 68(2) nm and the length L_a = 2.52(7) µm of the SbSI nanowires were determined. TiO₂ nanoparticles served as binders in the synthesized nanocomposite, which allowed for the preparation of dense films via the simple drop-casting method. The SbSI–TiO₂ nanocomposite film was sandwiched between gold and indium tin oxide (ITO) electrodes. The Curie temperature of T_C = 294(2) K was evaluated and confirmed to be consistent with the data reported in the literature for ferroelectric SbSI. The SbSI–TiO₂ device was subjected to periodic thermal fluctuations. The measured pyroelectric signals were highly correlated with the temperature change waveforms. The magnitude of the pyroelectric current was found to be a linear function of the temperature change rate. The high value of the pyroelectric coefficient p = 264(7) nC/(cm²·K) was determined for the SbSI–TiO₂ nanocomposite. When the rate of temperature change was equal dT/dt = 62.5 mK/s, the maximum and average surface power densities of the SbSI–TiO₂ nanogenerator reached 8.39(2) and 2.57(2) µW/m², respectively.

Dimensional measurement of TiO2 (Nano) particles by SAXS and SEM in powder form

The market for nano-additive materials has been growing exponentially since 2012, with almost 5040 consumer products containing nanoparticles in 2021. In parallel, the increasing recommendations, definitions and legislations underline the need for traceability of manufactured nanoparticles and for methods able to identify and quantify the "nano" dimensional character in manufactured product. From a multi-technic approach, this paper aims to compare the mesurands extracted from SAXS/BET (specific surface area) and SEM (diameter equivalent to a projected surface area) on different TiO₂ powder issued from referenced, synthesized materials, raw materials (additives) and extracted materials from manufactured products. The influence of various parameters such as the anisotropic factor, the interaction between particles, the size distribution and the extraction steps are discussed to illustrate their impact on the diameter values issued from two different measurands. These results illustrate the difficulties in (nano)particles characterization. SEM and SAXS are complementary techniques depending on the level of dimensional characterization required.

Single-nanometer iron oxide nanoparticles as tissue-permeable MRI contrast agents

Magnetic nanoparticles are robust contrast agents for MRI and often produce particularly strong signal changes per particle. Leveraging these effects to probe cellular- and molecular-level phenomena in tissue can, however, be hindered by the large sizes of typical nanoparticle contrast agents. To address this limitation, we introduce single-nanometer iron oxide (SNIO) particles that exhibit superparamagnetic properties in conjunction with hydrodynamic diameters comparable to small, highly diffusible imaging agents. These particles efficiently brighten the signal in T ₁-weighted MRI, producing per-molecule longitudinal relaxation enhancements over 10 times greater than conventional gadolinium-based contrast agents. We show that SNIOs permeate biological tissue effectively following injection into brain parenchyma or cerebrospinal fluid. We also demonstrate that SNIOs readily enter the brain following ultrasound-induced blood-brain barrier disruption, emulating the performance of a gadolinium agent and providing a basis for future biomedical applications. These results thus demonstrate a platform for MRI probe development that combines advantages of small-molecule imaging agents with the potency of nanoscale materials.

Silver Nanoparticle-Based Sensor for the Selective Detection of Nickel Ions

Silver nanoparticles (AgNPs) can be used as a surface plasmon resonance (SPR) colorimetric sensor; the correlation between the SPR phenomenon and the aggregation state of nanoparticle allows the real-time detection of a target molecule. Surface functionalization of NPs with proper molecular baits is often performed to establish the selectivity of the sensor. This work reports on the synthesis of AgNPs under reducing conditions and on the functionalization thereof with mercaptoundecanoic acid (11-MUA). UV-VIS Spectroscopy confirmed the formation of AgNPs, eliciting a surface plasmon absorption band (SPAB) at 393 nm that shifted to 417 nm upon surface coating. Dynamic light scattering was used to investigate the surface coatings; moreover, pelleted AgNPs@11MUA nanoparticles were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analyzers (EDX), and infrared spectroscopy to corroborate the presence of 11MUA on the surface. Most interestingly, the resulting AgNPs@11MUA selectively detected micromolar levels of Ni²⁺, also in the presence of other cations such as Mn²⁺, Co²⁺, Cd²⁺, Cu²⁺, Zn²⁺, Fe²⁺, Hg²⁺, Pb²⁺, and Cr³⁺.

The benefits of a Bayesian analysis for the characterization of magnetic nanoparticles

Magnetic nanoparticles offer a unique potential for various biomedical applications, but prior to commercial usage a standardized characterization of their structural and magnetic properties is required. For a thorough characterization, the combination of conventional magnetometry and advanced scattering techniques has shown great potential. In the present work, we characterize a powder sample of high-quality iron oxide nanoparticles that are surrounded with a homogeneous thick silica shell by DC magnetometry and magnetic small-angle neutron scattering (SANS). To retrieve the particle parameters such as their size distribution and saturation magnetization from the data, we apply standard model fits of individual data sets as well as global fits of multiple curves, including a combination of the magnetometry and SANS measurements. We show that by combining a standard least-squares fit with a subsequent Bayesian approach for the data refinement, the probability distributions of the model parameters and their cross correlations can be readily extracted, which enables a direct visual feedback regarding the quality of the fit. This prevents an overfitting of data in case of highly correlated parameters and renders the Bayesian method as an ideal component for a standardized data analysis of magnetic nanoparticle samples.

Comparative characterisation of non-monodisperse gold nanoparticle populations by X-ray scattering and electron microscopy

Accurate nanoparticle size determination is essential across various research domains, with many functionalities in nanoscience and biomedical research being size-dependent. Although electron microscopy is capable of resolving a single particle down to the sub-nm scale, the reliable representation of entire populations is plagued by challenges in providing statistical significance, suboptimal preparation procedures and operator bias. While alternative techniques exist that provide ensemble information in solution, their implementation is generally challenging for non-monodisperse populations. Herein, we explore the use of small-angle X-ray scattering in combination with form-free Monte Carlo fitting of scattering profiles as an alternative to conventional electron microscopy imaging in providing access to any type of core size distribution. We report on a cross-method comparison for quasi-monodisperse, polydisperse and bimodal gold nanoparticles of 2-7 nm in diameter and discuss advantages and limitations of both techniques.

The presence of iron oxide nanoparticles in the food pigment E172

Iron oxides used as food colorants are listed in the European Union with the number E172. However, there are no specifications concerning the fraction of nanoparticles in these pigments. Here, seven E172 products were thoroughly characterized. Samples of all colors were analyzed with a broad spectrum of methods to assess their physico-chemical properties. Small-Angle X-ray Scattering (SAXS), Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM), zeta-potential, Inductively Coupled Plasma-Mass Spectrometry (ICP-MS), X-ray diffraction (XRD), Brunauer-Emmett-Teller analysis (BET), Asymmetric Flow Field-Flow Fractionation (AF4) and in vitro cell viability measurements were used. Nanoparticles were detected in all E172 samples by TEM or SAXS measurements. Quantitative results from both methods were comparable. Five pigments were evaluated by TEM, of which four had a size median below 100 nm, while SAXS showed a size median below 100 nm for six evaluated pigments. Therefore, consumers may be exposed to iron oxide nanoparticles through the consumption of food pigments.

Thermodynamic stability condition can judge whether a nanoparticle dispersion can be considered a solution in a single phase

Establishing that a nanoparticle dispersion can, in fact, be treated as a solution has an important practical ramification, namely the application of solubility theories for solvent selection. However, what distinguishes a solution and dispersion has remained ambiguously understood. Based on the recent progress in statistical thermodynamics on multiple-component solutions, here we establish the condition upon which a nanoparticle dispersion can be considered a single-phased solution. We shall provide experimental evidence already found in the literature showing the solution nature of nanoparticle dispersions.

Combining surface chemistry modification and in situ small-angle scattering characterization to understand and optimize the biological behavior of nanomedicines

Monitoring structural transformation and quantity of NPs in biologically relevant environments with small-angle scattering techniques.

Microwave-Assisted Synthesis of Ultrasmall Zinc Oxide Nanoparticles

We report on ultrasmall zinc oxide single-crystalline nanoparticles of narrow size distribution and long-term colloidal stability. These oleate-stabilized nanoparticles were synthesized using microwave-assisted synthesis for 5 min, corresponding to a 99% decrease in synthesis time, when compared to the conventional synthesis method. It was observed that the average particle radius increases from 2.6 ± 0.1 to 3.8 ± 0.1 nm upon increasing synthesis temperature from 125 to 200 °C. This change also corresponded to observed changes in the optical band gap and the fluorescence energy of the particles, from 3.44 ± 0.01 to 3.36 ± 0.01 eV and from 2.20 ± 0.01 to 2.04 ± 0.01 eV, respectively. Small-angle X-ray scattering, dynamic light scattering, and UV-vis and fluorescence spectroscopy were employed for particle characterization. Debye-Scherrer analysis of the X-ray diffraction (XRD) pattern reveals a linear increase of the crystallite size with synthesis temperature. The consideration of the convolution of a Lorentz function with a Gaussian function for data correction of the instrumental peak broadening has a considerable influence on the values for the crystallite size. Williamson-Hall XRD analyses in the form of the uniform deformation model, uniform stress deformation model, and uniform deformation energy density model revealed a substantial increase of strain, stress, and deformation energy density of the crystallites with decreasing size. Exponential and power law models were utilized for quantification of strain, stress, and deformation energy density.

Characterization of Nanoparticles: Advances

Over the past two decades, the unique properties of engineered nanoparticles (NPs) have placed them at the centre of revolutionary advancements in many sectors of science, technology and commerce. Multi-technique and multi-disciplinary analytical approaches are required to identify, quantify, and characterize the chemical composition, size and size distribution, surface properties and the number and concentration of NPs. In this chapter, an overview of the recent advances in the characterization of NPs will be presented.

Small-angle scattering by supported nanoparticles: exact results and useful approximations

In functional materials, nanoparticles are often dispersed in a porous support for the purpose of stabilizing them. This makes their characterization by small-angle scattering challenging because the signal comprises contributions from the nanoparticles of interest, from the inert support and from their cross-correlation. Exact analytical expressions for all three contributions are derived in the case of a Gaussian-field model of the porous support, with nanoparticles randomly distributed over the surface. For low nanoparticle loading, the expressions simplify to the addition of properly scaled support and particle scattering. For higher loadings, however, the cross-correlation cannot be ignored. Two approximations are introduced, which capture correlation effects in cases where the pores of the support are much larger or only slightly larger than the nanoparticles. The methods of the paper are illustrated with the small-angle X-ray scattering analysis of hollow metallic nanoparticles supported on porous carbon.

Sticky Measurement Problem: Number Concentration of Agglomerated Nanoparticles

Measuring the number concentration of colloidal nanoparticles (NPs) is critical for assessing reproducibility, enabling compliance with regulation, and performing risk assessments of NP-enabled products. For nanomedicines, their number concentration directly relates to their dose. However, the lack of relevant reference materials and established traceable measurement approaches make the validation of methods for NP number concentration difficult. Furthermore, commercial products often exhibit agglomeration, but guidelines for dealing with nonideal samples are scarce. We have compared the performance of five benchtop measurement methods for the measurement of colloidal number concentration in the presence of different levels of agglomeration. The methods are UV-visible spectroscopy, differential centrifugal sedimentation, dynamic light scattering, particle tracking analysis, and single-particle inductively coupled plasma mass spectrometry. We find that both ensemble and particle-by-particle methods are in close agreement for monodisperse NP samples and three methods are within 20% agreement for agglomerated samples. We discuss the sources of measurement uncertainties, including how particle agglomeration affects measurement results. This work is a first step toward validation and expansion of the toolbox of methods available for the measurement of real-world NP products.

Number Concentration of Gold Nanoparticles in Suspension: SAXS and spICPMS as Traceable Methods Compared to Laboratory Methods

The industrial exploitation of high value nanoparticles is in need of robust measurement methods to increase the control over product manufacturing and to implement quality assurance. InNanoPart, a European metrology project responded to these needs by developing methods for the measurement of particle size, concentration, agglomeration, surface chemistry and shell thickness. This paper illustrates the advancements this project produced for the traceable measurement of nanoparticle number concentration in liquids through small angle X-ray scattering (SAXS) and single particle inductively coupled plasma mass spectrometry (spICPMS). It also details the validation of a range of laboratory methods, including particle tracking analysis (PTA), dynamic light scattering (DLS), differential centrifugal sedimentation (DCS), ultraviolet visible spectroscopy (UV-vis) and electrospray-differential mobility analysis with a condensation particle counter (ES-DMA-CPC). We used a set of spherical gold nanoparticles with nominal diameters between 10 nm and 100 nm and discuss the results from the various techniques along with the associated uncertainty budgets.

Measuring particle size distribution of nanoparticle enabled medicinal products, the joint view of EUNCL and NCI-NCL. A step by step approach combining orthogonal measurements with increasing complexity

The particle size distribution (PSD) and the stability of nanoparticles enabled medicinal products (NEP) in complex biological environments are key attributes to assess their quality, safety and efficacy. Despite its low resolution, dynamic light scattering (DLS) is the most common sizing technique since the onset of NEP in pharmaceutical technologies. Considering the limitations of the existing sizing measurements and the challenges posed by complex NEPs both scientists and regulators encourage the combination of multiple orthogonal high-resolution approaches to shed light in the NEP sizing space (e.g. dynamic light scattering, electron microscopy, field flow fractionation coupled to online sizing detectors, centrifugal techniques, particle tracking analysis and tunable resistive pulse sensing). The pharmaceutical and biotechnology developers are now challenged to find their own pragmatic characterisation approaches, which should be fit for purpose and minimize costs at the same time, in a complicated landscape where only a few standards exist. In order to support the community, the European Nanomedicine Characterisation Laboratory (EUNCL) and the US National Cancer Institute Nanotechnology Characterization Laboratory (NCI-NCL) have jointly developed multiple standard operating procedures (SOPs) for NEP assessment, including the measurements of particle size distribution, and are offering wide access to their 'state of the art' characterisation platforms, in addition to making SOPs publicly available. This joint perspective article would like to present the NCI-NCL and EUNCL multi-step approach of incremental complexity to measure particle size distribution and size stability of NEPs, consisting of a quick preliminary step to assess sample integrity and stability by low resolution techniques (pre-screening), followed by the combination of complementary high resolution sizing measurements performed both in simple buffers and in complex biological media. Test cases are presented to demonstrate: i) the need for employing at least one high-resolution sizing technique, ii) the importance of selecting the correct sizing techniques for the purpose, and iii) the robustness of utilizing orthogonal sizing techniques to study the physical properties of complex NEP samples.

Contribution to Accurate Spherical Gold Nanoparticle Size Determination by Single-Particle Inductively Coupled Mass Spectrometry: A Comparison with Small-Angle X-ray Scattering

Small-angle X-ray scattering spectroscopy (SAXS) is the method of choice for nanoparticle diameter and concentration determination. On the one hand, it is metrologically traceable for spherical nanoparticle mean diameter determination and does not require any sample preparation or calibration. On the other hand, single-particle inductively coupled mass spectrometry (SPICPMS) is still under development and requires involved process clarification and accuracy improvement. The strategy of this study is the comparison of the two techniques to study comprehensively SPICPMS performance and observe phenomena otherwise hidden. Six spherical gold nanoparticle suspensions distributed over a large size range (30, 50, 60, 80,100, and 150 nm) are studied as calibration points. Potential matrix effects are eliminated by stabilizing nanoparticles with chitosan in HCl. Chitosan encapsulates nanoparticles, stabilizes their dispersion, and protects them from dissolution. Detection counting/analogue threshold and timeout appear as the relevant parameters for transient signals. They show an influence not only on mean signal but also on signal distribution. The detection tuning proposed allows to linearly calibrate the nanoparticle distribution signal to cubed diameter over the entire range studied with no sensitivity diminution. Comparing the three classical transport efficiency methods, size transport efficiency is shown as the most accurate. The new procedure is validated analyzing three gold nanoparticle suspensions (135, 40, and 50 nm). The results are consistent with SAXS measurements.

Kinetic monitoring of glutathione-induced silver nanoparticle disintegration

We report on etching of polyacrylic acid-stabilised silver nanoparticles in the presence of glutathione (GSH). The initial particles with a radius of 3.2 nm and consisting of ∼8100 silver atoms dissolve in a two-step reaction mechanism while in parallel smaller silver particles with a radius of 0.65 nm and consisting of 60 to 70 silver atoms were formed. The kinetics of the etching of the initial particles, accompanied by formation of smaller silver particles was interpreted based on in situ, time-resolved small-angle X-ray scattering (SAXS) experiments.

Fate of Fluorescence Labels-Their Adsorption and Desorption Kinetics to Silver Nanoparticles

Silver nanoparticles are among the most widely used and produced nanoparticles. Because of their frequent application in consumer products, the assessment of their toxicological potential has seen a renewed importance. A major difficulty is the traceability of nanoparticles in in vitro and in vivo experiments. Even if the particles are labeled, for example, by a fluorescent marker, the dynamic exchange of ligands often prohibits their spatial localization. Our study provides an insight into the adsorption and desorption kinetics of two different fluorescent labels on silver nanoparticles with a core radius of 3 nm by dynamic light scattering, small-angle X-ray scattering, and fluorescence spectroscopy. We used BSA-FITC and tyrosine as examples for common fluorescent ligands. It is shown that the adsorption of BSA-FITC takes at least 3 days, whereas tyrosine adsorbs immediately. The quantitative amount of stabilizer on the particle surface was determined by fluorescence spectroscopy and revealed that the particles are stabilized by a monolayer of BSA-FITC (corresponding to 20 ± 9 molecules), whereas tyrosine forms a multilayered structure consisting of 15900 ± 200 molecules. Desorption experiments show that the BSA-FITC-stabilized particles are ideally suited for application in in vitro and in vivo experiments because the ligand desorption takes several days. Depending on the BSA concentration in the particles surroundings, the rate constant is k = 0.2 per day or lower when applying first order kinetics, that is, 50% of the BSA-FITC molecules are released from the particle's surface within 3.4 days. For illustration, we provide a first application of the fluorescence-labeled particles in an uptake study with two different commonly used cell lines, the human liver cell model HepG2 and the human intestinal cell model of differentiated Caco-2 cells.

Toxicological investigations of "naked" and polymer-entrapped AOT-based gold nanotriangles

Negatively charged ultrathin gold nanotriangles (AuNTs) were synthesized in a vesicular dioctyl sodium sulfosuccinate (AOT)/phospholipid-based template phase. These "naked" AuNTs with localized surface plasmon resonances in the NIR region at about 1300 nm and special photothermal properties are of particular interest for imaging and hyperthermia of cancerous tissues. For these kinds of applications the toxicity and the cellular uptake of the AuNTs is of outstanding importance. Therefore, this study focuses on the toxicity of "naked" AOT-stabilized AuNTs compared to polymer-coated AuNTs. Polymeric coating consisted of non-modified hyperbranched poly(ethyleneimine) (PEI), maltose-modified poly(ethyleneimine) (PEI-Mal) and heparin. The toxicological experiments were carried out with two different cell lines (embryonic kidney carcinoma cell line HEK293T and NK-cell leukemia cell line YTS). This study revealed that the heparin-coating of AuNTs improved biocompatibility by a factor of 50 when compared to naked AuNTs. Of note, the highest nontoxic concentration of the AuNTs coated with PEI and PEI-Mal is drastically decreased. Overall, this is mainly triggered by the different surface charges of polymeric coatings. Therefore, AuNTs coated with heparin were selected to carry out uptake studies. Their promising high biocompatibility and cellular uptake may open future studies in the field of biomedical applications.

What happens to the silver ions? - Silver thiocyanate nanoparticle formation in an artificial digestion

An artificial digestion of silver nitrate is reported. It is shown that AgSCN nanoparticles emerge from ionic silver in saliva and remain present during the entire digestion process. The particles were characterized by infrared spectroscopy and small- and wide-angle X-ray scattering (SAXS/WAXS) regarding their composition and size distribution.

The modular small-angle X-ray scattering data correction sequence

Data correction is probably the least favourite activity amongst users experimenting with small-angle X-ray scattering: if it is not done sufficiently well, this may become evident only during the data analysis stage, necessitating the repetition of the data corrections from scratch. A recommended comprehensive sequence of elementary data correction steps is presented here to alleviate the difficulties associated with data correction, both in the laboratory and at the synchrotron. When applied in the proposed order to the raw signals, the resulting absolute scattering cross section will provide a high degree of accuracy for a very wide range of samples, with its values accompanied by uncertainty estimates. The method can be applied without modification to any pinhole-collimated instruments with photon-counting direct-detection area detectors.