Polydisperse Solutions Research Articles

Unraveling the Dominant Size Effect in Polydisperse Solutions and Maximal Electric Field Enhancement of Gold Nanoparticles

Unraveling the Dominant Size Effect in Polydisperse Solutions and Maximal Electric Field Enhancement of Gold Nanoparticles

Characterization of polysulfides (Sx2−) in seawater euxinic conditions by electroanalytical methods

Polysulfides (Sx2−) are important reduced sulfur species (RSS) that play a role in numerous environmental processes. A sound analytical method for the measurement of Sx2− in euxinic waters is lacking. In this work, differential pulse voltammetry (DPV) at the Hg electrode was used to measure the presence of Sx2− in a model seawater solution and an euxinic marine lake (Rogoznica Lake - RL Croatia), in which the concentration of RSS, mainly HS−, varies between 100 and 4000 μM. In the DPV, an adsorption phenomenon associated with Sx2− reduction on Hg produces a characteristic current minimum at −1.0 V (vs. Ag/AgCl), the magnitude of which is proportional to the concentration of polysulfidic sulfur.The DPV current minima were recorded in the model solution K2Sx NaCl/NaHCO3 (pH ∼ 8.2) in a concentration range from 10 to 100 μM of polysulfidic sulfur. Total RSS was measured by cyclic voltammetry, and sampled DC voltammetry showed the ratio between HS− and S0 within the Sx2−. Using the same methodology, the presence of Sx2− below the chemocline enriched by photoptrophic sulfur bacteria was measured in the euxinic layer of RL at concentrations of up to 70 μM of polysulfidic sulfur. The results suggest that euxinic RL samples can be considered as polydisperse solutions of S0 or of S-rich compounds that can change their physicochemical properties and speciation during sample manipulation. These changes can be detected by electrochemistry. Atomic force microscopy proved the release of bacterial cellular S0 during the acidification and purging step in the electrochemical measurements, which contributed to the voltammetric RSS signal.

Solution Structures of Two Different FRP-OCP Complexes as Revealed via SEC-SANS.

Photosynthetic organisms have established photoprotective mechanisms in order to dissipate excess light energy into heat, which is commonly known as non-photochemical quenching. Cyanobacteria utilize the orange carotenoid protein (OCP) as a high-light sensor and quencher to regulate the energy flow in the photosynthetic apparatus. Triggered by strong light, OCP undergoes conformational changes to form the active red state (OCPR). In many cyanobacteria, the back conversion of OCP to the dark-adapted state is assisted by the fluorescence recovery protein (FRP). However, the exact molecular events involving OCP and its interaction with FRP remain largely unraveled so far due to their metastability. Here, we use small-angle neutron scattering combined with size exclusion chromatography (SEC-SANS) to unravel the solution structures of FRP-OCP complexes using a compact mutant of OCP lacking the N-terminal extension (∆NTEOCPO) and wild-type FRP. The results are consistent with the simultaneous presence of stable 2:2 and 2:1 FRP-∆NTEOCPO complexes in solution, where the former complex type is observed for the first time. For both complex types, we provide ab initio low-resolution shape reconstructions and compare them to homology models based on available crystal structures. It is likely that both complexes represent intermediate states of the back conversion of OCP to its dark-adapted state in the presence of FRP, which are of transient nature in the photocycle of wild-type OCP. This study demonstrates the large potential of SEC-SANS in revealing the solution structures of protein complexes in polydisperse solutions that would otherwise be averaged, leading to unspecific results.

Intracellular Fate of Sub-Toxic Concentration of Functionalized Selenium Nanoparticles in Aggressive Prostate Cancer Cells

Selenium 0 (Se0) is a powerful anti-proliferative agent in cancer research. We investigated the impact of sub-toxic concentrations of Se0 functionalized nanoparticles (SeNPs) on prostate cancer PC-3 cells and determined their intracellular localization and fate. An in-depth characterization of functionalized selenium nanoparticles composition is proposed to certify that no chemical bias relative to synthesis issues might have impacted the study. Selenium is an extremely diluted element in the biological environment and therefore requires high-performance techniques with a very low detection limit and high spatial resolution for intracellular imaging. This was explored with state-of-the-art techniques, but also with cryopreparation to preserve the chemical and structural integrity of the cells for spatially resolved and speciation techniques. Monodisperse solutions of SeNPs capped with bovine serum albumin (BSA) were shown to slow down the migration capacity of aggressive prostate cancer cells compared to polydisperse solutions of SeNPs capped with chitosan. BSA coating could prevent interactions between the reactive surface of the nanoparticles and the plasma membrane, mitigating the generation of reactive oxygen species. The intracellular localization showed interaction with mitochondria and also a localization in the lysosome-related organelle. The SeNPs-BSA localization in mitochondria constitute a possible explanation for our result showing a very significant dampening of the PC-3 cell proliferation capabilities. The purpose of the use of sublethal compound concentrations was to limit adverse effects resulting from high cell death to best evaluate some cellular changes and the fate of these SeNPs on PC-3. Our findings provide new insight to further study the various mechanisms of cytotoxicity of SeNPs.

Optical signal-based improvement of individual nanoparticle tracking analysis

Nanoparticle tracking analysis (NTA) provides a simple method to determine individual nanoparticle (NP) size. However, because size quantification is based on the slowly converging statistical law of random events, its intrinsic error is large, especially in the case of limited event numbers, e.g. for weak scattering NPs. Here, we introduce an NTA improvement by analyzing each individual NP trajectory while taking into account the other trajectories with a weighting coefficient. The weighting coefficient is directly derived from the optical signature of each particle measured by quantitative phase microscopy. Simulations and experimental results demonstrate the improvement in NTA accuracy, not only for mono-disperse but also for poly-disperse particle solutions.

Analysis of the physical and chemical properties of natural polysaccharides and the effect of dispersed glauconite mineral on them

The object of research is natural polysaccharides. One of the problems is the high cost and not always environmental friendliness of foreign analogues of these substances. Therefore, the methods of purification of polydisperse systems with the help of dispersed minerals, in particular separated dispersed mineral glauconite, purified and enriched up to 60 % of the initial content, are proposed. The study used aqueous solutions of dextran and pectin, which added glauconite in the amount of 0.3 to 0.9 % by weight of the solution, heated to 60 ºC and kept for 10 minutes. Using glauconite in the amount of 0.3 % by weight of the solution gave high quality indicators. Thus, the dependence of the viscosity of polysaccharides dextran and pectin on the concentration of the introduced mineral was studied. The lowest value of viscosity is observed when adding 0.3 % glauconite to the mass of the solution, with increasing concentration, the viscosity increases. The process of interaction of dextran molecules with the surface of glauconite is due to the fact that the proposed method of studying the viscosity has a feature that connects neighboring mineral particles through the dextran bridge and the formation of a stable gel structure. These structures are manifested in the form of partial groups of glauconite. This provides the ability to obtain such an indicator as adsorption. The mechanism of interaction of dextran with glauconite is confirmed by the dependence of the amount of dextran adsorbed on the surface of the mineral. Thus, at low concentrations of glauconite – up to 0.3 % adsorption of dextran on the surface increases, and with increasing concentration of glauconite – greatly decreases. This is crucial for the technological parameters of the mineral when using it in preparation processes, in comparison with similar adsorbents of unnatural origin. This will provide the benefits of glauconite over the use in the food industry and the regulation of the physicochemical properties of industrial polydisperse solutions as inexpensive additives of natural origin (stabilizers, thickeners, etc.) that are harmless to human health.

Integrated Approach with Small-angle Scattering and Component-separation Techniques for Structure of Biomacromolecules in Polydisperse and Multi-component Solutions

Integrated Approach with Small-angle Scattering and Component-separation Techniques for Structure of Biomacromolecules in Polydisperse and Multi-component Solutions

Angle-dependent effects in DLS measurements of polydisperse particles

Dynamic light scattering (DLS) is widely used for analyzing biological polymers and colloids. Its application to nanoparticles in medicine is becoming increasingly important with the recent emergence of prominent lipid nanoparticle (LNP)-based products, such as the SARS-CoV-2 vaccines from Pfizer, Inc.-BioNTech (BNT162b2) and Moderna, Inc. (mRNA-1273). DLS plays an important role in the characterization and quality control of nanoparticle-based therapeutics and vaccines. However, most DLS instruments have a single detection angle θ, and the amplitude of the scattering vector, q, varies among them according to the relationship q = (4πn/λ 0) sin(θ/2), where λ 0 is the laser wavelength. Results for identical, polydisperse samples among instruments of varying q yield different hydrodynamic diameters, because, as particles become larger they scatter less light at higher q, so that higher-q instruments will under-sample large particles in polydisperse populations, and report higher z-average diffusion coefficients, and hence smaller effective hydrodynamic diameters than lower-q instruments. As particle size reaches the Mie regime the scattering envelope manifests angular maxima and minima, and the monotonic decrease of average size versus q is lost. The discrepancy among instruments of different q is hence fundamental, and not merely technical. This work examines results for different q-value instruments, using mixtures of monodisperse latex sphere standards, for which experimental measurements agree well with computations, and also polydisperse solutions of physically-degraded LNPs, for which results follow expected trends. Mie effects on broad unimodal populations are also considered. There is no way to predict results between two instruments with different q for samples of unknown particle size distributions. Initial analysis of the polydispersity index among different instruments shows a technical difference due to method of autocorrelation analysis, in addition to the fundamental q-effect.

ESI-MS Identification of the Cationic Phosphine-Ligated Gold Clusters Au1-22: Insight into the Gold-Ligand Ratio and Abundance of Larger Clusters.

Triphenylphosphine (PPh3)-ligated gold nanoclusters are valuable for a number of potential applications due to their relative ease of synthesis and usefulness in forming advanced cluster architectures. While previous studies have reported cationic PPh3-ligated gold clusters with core sizes of Au1-4, Au6-11, and Au13-14, there has not been definitive identification by mass spectrometry of many larger clusters in the Au12-25 range. Herein, we survey a polydisperse solution of cationic PPh3-ligated gold clusters using high-mass-resolution (M/ΔM = 60,000) electrospray ionization mass spectrometry (ESI-MS). To improve the sensitivity and mass resolution of larger clusters for unambiguous identification, we increased the number of scan averages and reduced the range of mass collection windows to 200 m/z, thereby mitigating potential mass and ion abundance bias resulting from smaller "building block" gold clusters that are present in much higher abundance in solution. In addition to the previously reported clusters, we identify several new species including Au5(PPh3)5+, Au12(PPh3)9HCl2+, Au15(PPh3)9Cl2+, Au16(PPh3)10Cl22+, Au17(PPh3)113+, Au18(PPh3)102+, Au19(PPh3)10Cl2+, Au20(PPh3)12H33+, Au21(PPh3)10Cl2+, and Au22(PPh3)10Cl22+, indicating that a full range of clusters between Au1-22 may be observed in a single polydisperse solution. Considering all of the clusters observed, our findings provide evidence that the Au12-14 size range is a critical transition point in cluster nucleation. While smaller clusters exhibit a 1:1 gold-to-ligand ratio, larger clusters (beginning Au12-14) feature additional gold atoms without an equal number of accompanying ligands. Our results support previous evidence in the literature indicating that the "magic number" icosahedral Au13 geometry is the smallest cluster size where a ligand-less central gold atom is coordinated by a complete shell of 12 surrounding ligated gold atoms, thereby creating a stable "one-shell" cluster. Furthermore, our findings reinforce growing evidence that ligands may be used to actively direct gold cluster size and abundance during synthesis. While for PPh3-ligated systems the most abundant species are Au6-9 clusters, we find that for related methyldiphenylphosphine (PPh2Me) and dimethylphenylphosphine (PPhMe2)-ligated systems the most abundant cluster sizes are Au10-11 and Au12-14, respectively. Together, we demonstrate that reducing the range of m/z collection windows and increasing the number of scan averages dramatically improves instrument sensitivity for cationic gold clusters, enabling thorough characterization of polydisperse solutions that is not possible using conventional techniques.

Multispectral Nanoparticle Tracking Analysis for the Real-Time and Label-Free Characterization of Amyloid-β Self-Assembly In Vitro.

The deposition of amyloid β (Aβ) plaques and fibrils in the brain parenchyma is a hallmark of Alzheimer's disease (AD), but a mechanistic understanding of the role Aβ plays in AD has remained unclear. One important reason could be the limitations of current tools to size and count Aβ fibrils in real time. Conventional techniques from molecular biology largely use ensemble averaging; some microscopy analyses have been reported but suffer from low throughput. Nanoparticle tracking analysis is an alternative approach developed in the past decade for sizing and counting particles according to their Brownian motion; however, it is limited in sensitivity to polydisperse solutions because it uses only one laser. More recently, multispectral nanoparticle tracking analysis (MNTA) was introduced to address this limitation; it uses three visible wavelengths to quantitate heterogeneous particle distributions. Here, we used MNTA as a label-free technique to characterize the in vitro kinetics of Aβ1-42 aggregation by measuring the size distributions of aggregates during self-assembly. Our results show that this technology can monitor the aggregation of 106-108 particles/mL with a temporal resolution between 15 and 30 min. We corroborated this method with the fluorescent Thioflavin-T assay and transmission electron microscopy (TEM), showing good agreement between the techniques (Pearson's r = 0.821, P < 0.0001). We also used fluorescent gating to examine the effect of ThT on the aggregate size distribution. Finally, the biological relevance was demonstrated via fibril modulation in the presence of a polyphenolic Aβ disruptor. In summary, this approach measures Aβ assembly similar to ensemble-type measurements but with per-fibril resolution.

Octamers participation in the formation of lysozyme ordered layers from crystallization solutions

The results of the study of thin film ordered protein structures formed from polydisperse solutions of lysozyme using Langmuir technology are presented. The proposed method for producing protein films is based on a modification of the Langmuir-Schaeffer method, which consists in using a pre-prepared protein solution with the addition of a precipitant. The pre-prepared protein solutions’ parameters (protein and precipitant concentrations, buffer type, etc.) correspond to protein crystallization conditions. It is assumed that protein oligomers formed in the solution as a result of the addition of the precipitant (in particular, for lysozyme these oligomers include octamers) are directly involved in the formation of Langmuir protein layers on the surface of the liquid and on solid substrates. Using the method of grazing-incidence X-ray standing waves, the structure of multilayered protein systems formed from polydisperse solutions was studied, which made it possible to determine directly the position of precipitant ions (NaCl, CuCl2 and NiCl2) relative to the protein layer. The method of processing the X-ray reflectivity and grazing-incidence X-ray standing waves data, based on the use of information on the atomic structure of lysozyme octamers isolated from the crystal lattice, made it possible to determine the thickness and electron density of protein films and to reveal the orientation of protein molecules in the layer.

Modelling polydisperse nanoparticle size distributions as produced via flame spray pyrolysis

The correct description of the particulates produced via the flame spray pyrolysis (FSP) process is essential for scale-up studies and new reactor design. With the combination of computational fluid dynamics (CFD) and population balance models (PBM) it is possible to predict the formation and evolution of nanoparticles in such reactors, and estimate final product characteristics. The solution of such PBM, however, can be very costly, given the fact that the phenomena involved in the process require for a bivariate approach. In this work, the direct quadrature method of moments (DQMoM) is employed in order to obtain a polydisperse solution of the PBM, due to its relatively straight forward adaptation from uni- to bivariate cases. Furthermore, the reacting turbulent multiphase flow of the burning spray is described by an Eulerian-Lagrangian framework and solved with the use of CFD. The production of zirconium dioxide nanoparticles from a solution of zirconium n-propoxide in ethanol and propanol is investigated, and experimental data obtained through transmission electron microscopy (TEM) is used for model validation. Accuracy of about 90% is obtained for the first two moments of the distribution and the number of primary particles per agglomerate show good agreement with experiments.

Suspended Nanochannel Resonator Arrays with Piezoresistive Sensors for High-Throughput Weighing of Nanoparticles in Solution.

As the use of nanoparticles is expanding in many industrial sectors, pharmaceuticals, cosmetics among others, flow-through characterization techniques are often required for in-line metrology. Among the parameters of interest, the concentration and mass of nanoparticles can be informative for yield, aggregates formation or even compliance with regulation. The Suspended Nanochannel Resonator (SNR) can offer mass resolution down to the attogram scale precision in a flow-through format. However, since the readout has been based on the optical lever, operating more than a single resonator at a time has been challenging. Here we present a new architecture of SNR devices with piezoresistive sensors that allows simultaneous readout from multiple resonators. To enable this architecture, we push the limits of nanofabrication to create implanted piezoresistors of nanoscale thickness (∼100 nm) and implement an algorithm for designing SNRs with dimensions optimized for maintaining attogram scale precision. Using 8-in. processing technology, we fabricate parallel array SNR devices which contain ten resonators. While maintaining a precision similar to that of the optical lever, we demonstrate a throughput of 40 000 particles per hour-an order of magnitude improvement over a single device with an analogous flow rate. Finally, we show the capability of the SNR array device for measuring polydisperse solutions of gold particles ranging from 20 to 80 nm in diameter. We envision that SNR array devices will open up new possibilities for nanoscale metrology by measuring not only synthetic but also biological nanoparticles such as exosomes and viruses.

Functional ethanol-induced fibrils: Influence of solvents and temperature on amyloid-like aggregation of beta-lactoglobulin

Solvent-induced fibrillar aggregates of beta-lactoglobulin occur only in a certain balance between hydrophobic forces and electrostatic interactions. We hypothesize, that different hydrophobic solvent molecules as well as rising temperatures influence this equilibrium and thus the optimum to produce amyloid aggregates.Dimethyl sulfoxide (DMSO), methanol and ethanol all resulted in polydisperse solutions with worm-like and spherical-aggregates, albeit to different degrees: the volume fraction required for aggregation was DMSO (50%) > methanol (40%) > ethanol (30%) which does not reflect their hydrophobicity. Further solvent addition decreased the fibrillar aggregation again. Increasing the temperature by 10–20 K decreased the solvent concentration needed to induce amyloid-like aggregates.A targeted production of solvent-based amyloid-like aggregates is therefore not only dependent on the hydrophobicity of the solvents, but also on their direct interaction with the protein (denaturation).

Acid hydrolysis of corn starch genotypes. II. Impact on functional properties

The impact of the acid modification on the molecular properties of two corn starch genotypes (high amylose corn starch: HACS, amylose (AM) content about 70% w/w; waxy corn starch: WxCS, AM content < 2% w/w) was reported comprehensively in a previous study. Based on that, the data referring to the solution and the gel properties, which are important attributes for the application in e.g. gelled sweets, were presented in the present study. Polydisperse solutions were prepared by pressure cooking. The hot paste viscosity (η) of the concentrated native HACS solution was significantly higher compared to WxCS. The reduction of the weight average molar mass (Mw) due to acid-thinning reduced η by trend (WxCS). Native HACS tends to form very stable gels. However, acid-thinning reduced the stability of the gel system slightly. The non-gelling character of the WxCS wasn't changed either by the modification. Furthermore, the light transmittance differed strongly depending on the type of starch variety. Independent of the state, i.e. either the freshly prepared solution or the corresponding cold stored product, the HACS samples were generally turbid and the WxCS samples of high clarity. The specificity of the functionality in blends basically behaved according to the mixing ratio of the two genotypes. However, increasing relative portions of amylopectin (AP) reduced the ability to inter-chain associations and resulting gel hardness disproportionally on the one hand, but the light transmittance didn't increase adequately on the other hand.

On approximation and experimental accuracy in dynamic light scattering

The work is dedicated to estimation of accuracy of calculations in dynamic light scattering experiments, in particular approximation and size determination of nanoparticles in polydisperse solutions. In dynamic light scattering the proper approximation is crucial to final accuracy of sizes calculations, especially if we consider polydisperse solutions, such as biological fluids. Calculated and experimental errors have been compared.

Protein Short-Time Diffusion in a Naturally Crowded Environment.

The interior of living cells is a dense and polydisperse suspension of macromolecules. Such a complex system challenges an understanding in terms of colloidal suspensions. As a fundamental test we employ neutron spectroscopy to measure the diffusion of tracer proteins (immunoglobulins) in a cell-like environment (cell lysate) with explicit control over crowding conditions. In combination with Stokesian dynamics simulation, we address protein diffusion on nanosecond time scales where hydrodynamic interactions dominate over negligible protein collisions. We successfully link the experimental results on these complex, flexible molecules with coarse-grained simulations providing a consistent understanding by colloid theories. Both experiments and simulations show that tracers in polydisperse solutions close to the effective particle radius Reff = ⟨ Ri3⟩1/3 diffuse approximately as if the suspension was monodisperse. The simulations further show that macromolecules of sizes R > Reff ( R < Reff) are slowed more (less) effectively even at nanosecond time scales, which is highly relevant for a quantitative understanding of cellular processes.

Restoring silicasol structural parameters using gradient and simulation annealing optimization schemes from small-angle X-ray scattering data

The performance of different optimization schemes for structural characterization of polydisperse mixtures using small-angle X-ray scattering (SAXS) data from silicasol nanoparticles in solution is studied. The simulated annealing algorithm is compared with the Broyden–Fletcher–Goldfarb–Shanno variable metric method with simple bounds on the model parameters. The results of the performed simulations point to high performance of both methods and at the same time to certain limitations of them depending on different starting approximations. This study will help one to choose a most efficient optimization algorithm and deduce recommendations for the optimal minimization schemes that permit one to reliably restore the volume size distributions for polydisperse solutions of nanoparticles.

High-Resolution Nanoparticle Sizing with Maximum A Posteriori Nanoparticle Tracking Analysis.

The rapid and efficient characterization of polydisperse nanoparticle dispersions remains a challenge within nanotechnology and biopharmaceuticals. Current methods for particle sizing, such as dynamic light scattering, analytical ultracentrifugation, and field-flow fractionation, can suffer from a combination of statistical biases, difficult sample preparation, insufficient sampling, and ill-posed data analysis. As an alternative, we introduce a Bayesian method that we call maximum a posteriori nanoparticle tracking analysis (MApNTA) for estimating the size distributions of nanoparticle samples from high-throughput single-particle tracking experiments. We derive unbiased statistical models for two observable quantities in a typical nanoparticle trajectory-the mean square displacement and the trajectory length-as a function of the particle size and calculate size distributions using maximum a posteriori (MAP) estimation with cross validation to mildly regularize solutions. We show that this approach infers nanoparticle size distributions with high resolution by performing extensive Brownian dynamics simulations and experiments with mono- and polydisperse solutions of gold nanoparticles as well as single-walled carbon nanotubes. We further demonstrate particular utility for characterizing minority components and impurity populations and highlight this ability with the identification of an impurity in a commercially produced gold nanoparticle sample. Modern algorithms such as MApNTA should find widespread use in the routine characterization of complex nanoparticle dispersions, allowing for significant advances in nanoparticle synthesis, separation, and functionalization.

Separation of particles by size from a suspension using the motion of a confined bubble

When confined in a liquid-filled circular cylinder, a long air bubble moves slightly faster than the bulk liquid as a small fraction of the liquid leaks through a very thin annular gap between the bubble and the internal wall of the cylinder. At low velocities, the thickness of this lubricating film formed around the bubble is set only by the liquid properties and the translational speed of the bubble and thus can be tuned in a simple fashion. Here, we use this setting to filter, based on size, micron-size particles that are originally dispersed in a suspension. Furthermore, we apply this process for separation of particles from a polydisperse solution. The bubble interface is free of particles initially, and particles of different sizes can enter the liquid film region. Particle separation occurs when the thickness of the lubricating liquid film falls between the diameters of the two different particles. While large particles will be collected at the bubble surface, smaller particles can leak through the thin film and reach the fluid region behind the bubble. As a result, the film thickness can be fine-tuned by simply adjusting the speed of a translating confined bubble, so as to achieve separation of particles by size based on the relative particle diameter compared to the film thickness.