Growth Kinetics Of Nanoparticles Research Articles

Development of novel lipoplex formulation methodologies to improve large-scale transient transfection for lentiviral vector manufacture

Large-scale transient transfection has advanced significantly over the last 20 years, enabling the effective production of a diverse range of biopharmaceutical products, including viral vectors. However, a number of challenges specifically related to transfection reagent stability and transfection complex preparation times, remain. New developments and improved transfection technologies are required to ensure that transient gene expression-based bioprocesses can meet the growing demand for viral vectors. In this paper we demonstrate the growth of cationic lipid-based liposomes, an essential step in many cationic lipid-based transfection processes, can be controlled through adoption of low pH (pH 6.40 – pH 6.75) and in low salt concentration (0.2X PBS) formulations, facilitating improved control over the nanoparticle growth kinetics and enhancing particle stability. Such complexes retain the ability to facilitate efficient transfection for prolonged periods compared to standard preparation methodologies. These findings have significant industrial applications for the large-scale manufacture of lentiviral vectors for two principal reasons. First, the alternative preparation strategy enables longer liposome incubation times to be used, facilitating effective control in a GMP setting. Second, the improvement in particle stability facilitates the setting of wider process operating ranges, which will significantly improve process robustness and maximise batch-to-batch control and product consistency.

Troubleshooting the influence of trace chemical impurities on nanoparticle growth kinetics via electrochemical measurements.

Reproducibility issues resulting from particle growth solutions made with cetyltrimethylammonium bromide (CTAB) surfactant from different lots and product lines in a newly developed synthesis of monometallic palladium (Pd) tetrahexahedra (THH) nanoparticles are investigated via a multi-pronged approach. Time-resolved electrochemical measurements of solution potential, variation of chemical parameters in colloidal synthesis, and correlation to electrodeposition syntheses are used together to uncover the effects of the unknown contaminants on the chemical reducing environment during nanoparticle growth. Iodide-a known impurity in commercial CTAB-is identified as one of the required components for equalizing the reducing environment across multiple CTAB sources. However, an additional component-acetone-is critical to establishing the growth kinetics necessary to enable the reproducible synthesis of THH in each of the CTAB formulations. In one CTAB variety, the powdered surfactant contains too much acetone, and drying of the as-received surfactant and re-addition of solvent is necessary for successful Pd THH synthesis. The relevance of solvent impurities to the reducing environment in aqueous nanoparticle synthesis is confirmed via electrochemical measurement approaches and solvent addition experiments. This work highlights the utility of real-time electrochemical potential measurements as a tool for benchmarking of nanoparticle syntheses and troubleshooting of reproducibility issues. The results additionally emphasize the importance of considering organic solvent impurities in powdered commercial reagents as a possible shape-determining factor during shaped nanomaterials synthesis.

Visualizing formation of high entropy alloy nanoparticles with liquid phase transmission electron microscopy.

High entropy alloy (HEA) nanoparticles hold promise as active and durable (electro)catalysts. Understanding their formation mechanism will enable rational control over composition and atomic arrangement of multimetallic catalytic surface sites to maximize their activity. While prior reports have attributed HEA nanoparticle formation to nucleation and growth, there is a dearth of detailed mechanistic investigations. Here we utilize liquid phase transmission electron microscopy (LPTEM), systematic synthesis, and mass spectrometry (MS) to demonstrate that HEA nanoparticles form by aggregation of metal cluster intermediates. AuAgCuPtPd HEA nanoparticles are synthesized by aqueous co-reduction of metal salts with sodium borohydride in the presence of thiolated polymer ligands. Varying the metal : ligand ratio during synthesis showed that alloyed HEA nanoparticles formed only above a threshold ligand concentration. Interestingly, stable single metal atoms and sub-nanometer clusters are observed by TEM and MS in the final HEA nanoparticle solution, suggesting nucleation and growth is not the dominant mechanism. Increasing supersaturation ratio increased particle size, which together with observations of stable single metal atoms and clusters, supported an aggregative growth mechanism. Direct real-time observation with LPTEM imaging showed aggregation of HEA nanoparticles during synthesis. Quantitative analyses of the nanoparticle growth kinetics and particle size distribution from LPTEM movies were consistent with a theoretical model for aggregative growth. Taken together, these results are consistent with a reaction mechanism involving rapid reduction of metal ions into sub-nanometer clusters followed by cluster aggregation driven by borohydride ion induced thiol ligand desorption. This work demonstrates the importance of cluster species as potential synthetic handles for rational control over HEA nanoparticle atomic structure.

Growth of Colloidal Nanocrystals by Liquid-Like Coalescence*.

We here describe, model, and predict the growth kinetics of amine-capped PbS colloidal nanoparticles in the absence of supersaturation. The particles grow by coalescence rather than by Ostwald ripening. A comparison of different models indicates that the effective activation energy of coalescence (67.65 kJ mol-1 ) is associated with two terms: a term proportional to the contact area between the ligand shells of two colliding particles, and a constant term. Our Brownian dynamics simulations show (i) how the remarkably low activation energy (or large rate constants) are most likely due to the large difference in size between the particles and their mean free path of diffusion, and (ii) how the low polydispersity is the likely result of the suppression of collision rates between rare populations due to crowding. The model successfully predicts the growth kinetics of nanoparticles, therefore enabling the precise control of the average particle size without the need of supersaturation.

Growth of Colloidal Nanocrystals by Liquid‐Like Coalescence**

AbstractWe here describe, model, and predict the growth kinetics of amine‐capped PbS colloidal nanoparticles in the absence of supersaturation. The particles grow by coalescence rather than by Ostwald ripening. A comparison of different models indicates that the effective activation energy of coalescence (67.65 kJ mol−1) is associated with two terms: a term proportional to the contact area between the ligand shells of two colliding particles, and a constant term. Our Brownian dynamics simulations show (i) how the remarkably low activation energy (or large rate constants) are most likely due to the large difference in size between the particles and their mean free path of diffusion, and (ii) how the low polydispersity is the likely result of the suppression of collision rates between rare populations due to crowding. The model successfully predicts the growth kinetics of nanoparticles, therefore enabling the precise control of the average particle size without the need of supersaturation.

Growth of nanoparticles in dynamic plasma.

Coagulation growth kinetics of nanoparticles in plasma is affected by interparticle electrostatic forces due to the charging phenomenon. In stationary plasmas, unipolar charging of particles results in retardation of particle growth and may result in a limitation on particle size. We demonstrate the opposite effect of enhanced particle growth in atmospheric pressure nonstationary arc discharge. Modeling of the nanoparticle growth kinetics reveals the formation of a bipolar charge distribution. As a result, reversed (attractive) Coulomb forces promote the formation of micrometer-size particles in a millisecond timescale as observed in experiment.

Confinement induced formation of silver nanoparticles in self-assembled micro-granules

Effect of nanoscale confinement on the formation of Ag nanoparticles in porous matrix of nanostructured silica micro-granules has been investigated. One step rapid drying of tiny aerosol droplets has been employed for incorporation of metal precursor in the porous micro-granules. The formation of nanoparticles in the confined geometry of interstitial granular pores has been revealed by small-angle scattering and field-emission scanning electron microscopy. It has been observed that nanometric confinement accelerates the chemical reduction of precursor as compared to that in a bulk solution and the formation yield gets further enhanced by irradiation of X-ray. The growth kinetics of nanoparticles has been probed by time-resolved scattering experiments. It is revealed that X-ray-induced dissociation of bound water in the granular interstices produces hydrated electrons favouring the reduction reaction.

Facile synthesis of gold nanoparticles in aqueous acrylamide solution

A method is advanced for preparing gold nanoparticles (NPs) at 50°C in aqueous acrylamide (AAm), which has the dual function of a reducing agent for HAuCl4 and a protective ligand for NPs. Nanoparticles have gold cores with the average size d Au = 20.9 ± 3.6 nm. The growth kinetics of NPs has been studied. Films of NPs have been produced on glass, silica, silicon, and polyethylene terephthalate (PET) substrates. The NPs and films have been characterized by UV-Vis and IR spectroscopy, X-ray powder diffraction, transmission and scanning electron microscopy, and atomic-force microscopy.

Growth kinetics of [formula omitted] particles in [formula omitted]-Ti matrix studied by in situ small-angle X-ray scattering

Nucleation and growth kinetics of nanoparticles of hexagonal ω phase in a body-centered cubic β titanium matrix in single crystals of β-Ti alloys were investigated by small-angle X-ray scattering measured in situ during ageing at various temperatures up to 450°C. The experimental data were compared with numerical simulations based on a three-dimensional short-range order model of nanoparticle self-ordering. The X-ray contrast of the particles is caused by an inhomogeneous distribution of impurity atoms (Mo, Fe and Al), whose density profile around growing nanoparticles was simulated by solving the corresponding diffusion equation with moving boundary conditions. From the analysis of the experimental data we determined the mean distance and size of the nanoparticles and confirmed the validity of the ∝t1/3 growth law following from the Lifshitz–Slyozov–Wagner theory. From a detailed comparison of the experimental data with simulations we also assessed the diffusion coefficient of the impurity atoms and its activation energy.

Comparison of the neutron and ion irradiation response of nano-oxides in oxide dispersion strengthened materials

Abstract

Spectroscopic studies of nucleic acid additions during seed-mediated growth of gold nanoparticles.

The effect of adding nucleic acids to gold seeds during the growth stage of either nanospheres or nanorods was investigated using UV-Vis spectroscopy to reveal any oligonucleotide base or structure-specific effects on nanoparticle growth kinetics or plasmonic signatures. Spectral data indicate that the presence of DNA duplexes during seed ageing drastically accelerated nanosphere growth while the addition of single-stranded polyadenine at any point during seed ageing induces nanosphere aggregation. For seeds added to a gold nanorod growth solution, single-stranded polythymine induces a modest blue-shift in the longitudinal peak wavelength. Moreover, a particular sequence comprised of 50% thymine bases was found to induce a faster, more dramatic blue-shift in the longitudinal peak wavelength compared to any of the homopolymer incubation cases. Monomeric forms of the nucleic acids, however, do not yield discernable spectral differences in any of the gold suspensions studied.

Growth Kinetics of Concave Nanocubes Studied by Optical Coherence Tomography

This work presents the analysis of the growth kinetics of two syntheses of concave gold nanocubes with a mean size of 72 and 108 nm followed by the optical coherence tomography (OCT) technique by acquiring B-scan images each 5 s. In addition, ultra violet-visible (UV-Vis) spectra and mean size from dynamic light scattering (DLS) were acquired during nanoparticle growth to generate kinetic plots in order to corroborate the OCT results. Kinetic plots from OCT images were obtained by plotting contrast enhancement of B-scan images as function of time. Fitting parameters values given by using the classical Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation show that the growth rate parameter k is higher for small cubes than for large ones, and that the Avrami exponent n associated to the growth kinetics of concave nanocubes is close to 2 for both syntheses. The results of UV-Vis spectroscopy and DLS confirm that OCT is a viable technique to provide information about nanoparticle growth kinetics. Moreover, to our knowledge, this is the first time that OCT technique is used to follow nanoparticle growth kinetics.

One-Pot Synthesis of Trimetallic Au@PdPt Core–Shell Nanoparticles with High Catalytic Performance

The development of an efficient synthesis method to produce multimetallic nanoparticles (NPs) with a desirable structure is strongly required to clarify the structure-composition-property relationship of NPs and to investigate their possible applications. However, the controlled synthesis of NPs consisting of multiple (n ≥ 3) noble metal components has been relatively unexplored in comparison to bimetallic NPs. In the present work, we have demonstrated a facile one-pot aqueous approach for the controlled synthesis of trimetallic Au@PdPt core-shell NPs with a well-defined octahedral Au core and a highly crystalline dendritic Pd-Pt alloy shell (Auoct@PdPt NPs). The simultaneous reduction of multiple metal precursors with dual reducing agents, namely, ascorbic acid and hydrazine, gave a fine control over the nucleation and growth kinetics of NPs, resulting in the formation of novel Auoct@PdPt NPs. The prepared NPs showed excellent catalytic performance for methanol electrooxidation, which can be attributed to their optimized binding strength toward adsorbate molecules due to the improved charge transfer between core and shell of the NPs. The present strategy can offer a convenient and valuable way to fabricate multicomponent nanostructures with desired structures and functions.

Correlated Optical Spectroscopy and Electron Microscopy Studies of the Slow Ostwald-Ripening Growth of Silver Nanoparticles under Controlled Reducing Conditions

Metallic nanoparticles display distinct localized surface plasmon resonance (LSPR) properties that depend on their size, shape, and composition and that can be monitored to characterize their growth. Utilizing LSPR properties, we report the first investigation of ambient temperature formation of trioctylamine (TOA)-stabilized spherical silver nanoparticles (AgNPs) of ∼3.0-nm diameter by mild reduction of AgClO4 with the weak reducing agent heptamethyltrisiloxane in organic solvent. The appropriate choice of experimental conditions caused slow reduction, which allowed the study of the nanoparticle growth process by time-resolved UV–visible spectroscopy and transmission electron microscopy (TEM). The linear nanoparticle growth kinetics from 50 min to end of the reaction derived from LSPR changes, the absence of a bimodal size distribution during the initial stage of the reduction process from TEM analysis, and the single crystallinity of the resulting AgNPs suggested a diffusion-controlled Ostwald-ripening growth process. It was also found that in addition to its stabilizing ability, TOA acted as a catalyst and facilitated Ag+ reduction. Furthermore, a modest increase in reaction temperature caused a substantial enhancement in the AgNP formation rate, and low concentration of stabilizing ligand yielded an increase in size and dispersity.

Direct synthesis of coated gold nanoparticles mediated by polymers with amino groups

The single-step/single-phase synthesis of hybrid organic–inorganic core–shell gold nanoparticles (AuNPs), facilitated by amino-functionalized amphiphilic block copolymers that simultaneously play the roles of reductant and stabilizer, was investigated in this study. Experiments were devised with emphasis on the pH-responsive poly(ethylene oxide)-b-poly(2,3-dihydroxypropyl methacrylate)-b-poly[2-(diisopropylamino)ethyl methacrylate] triblock copolymer, which allows direct chemical cross-linking of the micellar structures to be performed. The polymer structure–reactivity relationship associated with the AuNP formation was established using a set of six structurally related macromolecules. AuNP formation was dependent on the aqueous dissociation equilibrium involving tertiary amino groups, the Au(III) speciation, and electrochemical redox potentials. The effects of these parameters on the synthesis of AuNPs change as the solution pH is increased from pH 3.3 (molecularly dissolved polymer chains; no AuNP formation) to 6.8 or higher (polymer chains self-assembled into spherical micelles; stable gold sols are produced), and Au(III) reduction potentials shift toward the cathodic region while the oxidation potential of deprotonated amino groups decreases. Sigmoidal nanoparticle growth kinetics was observed in all cases after a characteristic induction period. Stable, well-defined, uniform polymer-coated gold colloids with localized surface plasmon resonance centered at 530nm can be conveniently produced in one-pot, two-reactant, no work-up reactions when the stoichiometry is [N]/[Au]=3.5–25.0.

Beneficial Effects of Microwave-Assisted Heating versus Conventional Heating in Noble Metal Nanoparticle Synthesis

An extensive comparative study of the effects of microwave versus conventional heating on the nucleation and growth of near-monodisperse Rh, Pd, and Pt nanoparticles has revealed distinct and preferential effects of the microwave heating method. A one-pot synthetic method has been investigated, which combines nucleation and growth in a single reaction via precise control over the precursor addition rate. Using this method, microwave-assisted heating enables the convenient preparation of polymer-capped nanoparticles with improved monodispersity, morphological control, and higher crystallinity, compared with samples heated conventionally under otherwise identical conditions. Extensive studies of Rh nanoparticle formation reveal fundamental differences during the nucleation phase that is directly dependent on the heating method; microwave irradiation was found to provide more uniform seeds for the subsequent growth of larger nanostructures of desired size and surface structure. Nanoparticle growth kinetics are also markedly different under microwave heating. While conventional heating generally yields particles with mixed morphologies, microwave synthesis consistently provides a majority of tetrahedral particles at intermediate sizes (5-7 nm) or larger cubes (8+ nm) upon further growth. High-resolution transmission electron microscopy indicates that Rh seeds and larger nanoparticles obtained from microwave-assisted synthesis are more highly crystalline and faceted versus their conventionally prepared counterparts. Microwave-prepared Rh nanoparticles also show approximately twice the catalytic activity of similar-sized conventionally prepared particles, as demonstrated in the vapor-phase hydrogenation of cyclohexene. Ligand exchange reactions to replace polymer capping agents with molecular stabilizing agents are also easily facilitated under microwave heating, due to the excitation of polar organic moieties; the ligand exchange proceeds with excellent retention of nanoparticle size and structure.

Atomistic simulations of Au-silica nanocomposite film growth

The growth of Au-silica nanocomposite film is simulated in the framework of kinetic three dimensional lattice Monte Carlo simulations considering the basic phenomena in the deposition process. In case of co-sputter deposition, the growth kinetics of nanoparticles has been studied taking into consideration the effect of the energetic sputtered species reaching the surface of the film during deposition. Formation of Au nanorod like structures are predicted under certain growth conditions particularly when surface diffusion assisted phase separation plays the dominant role and bulk kinetics is frozen. The observed dependence of the Au nanoparticle size on Au/silica ratio is in agreement with the experimental results.

Pathway from a Molecular Precursor to Silver Nanoparticles: The Prominent Role of Aggregative Growth

A mechanistic study of Ag-nanoparticle growth by reaction of [(PPh3)2Ag(O2CC13H27)] and AIBN is reported. The half-life for precursor disappearance at 130.0 ± 0.1 °C under the reaction conditions is determined to be 3.65 ± 0.42 min, which defines the time scale for classical (LaMer) nucleation and growth to be within the first 15 min (4 half-lives). The nanoparticle-growth kinetics are separately determined by TEM monitoring and UV−visible spectroscopy. Fits to the kinetic data establish that the active-growth regime extends to 58 min, and that Ostwald ripening ensues shortly thereafter. Evidence for an aggregative nucleation and growth process is obtained. The quantitative data indicate that classical nucleation and growth, aggregative nucleation and growth, and Ostwald ripening occur in consecutive time regimes with little overlap, and that nanoparticle growth is dominated by the aggregative regime. Aggregative growth should be considered a potential contributing mechanism in all nanoparticle-forming re...

Real time monitoring of the in situ growth of silver nanoparticles in a polymer film under ambient conditions

Direct monitoring of the formation and growth of nanoparticles by microscopy in real time is of fundamental interest in understanding the chemical and self assembly processes involved. Such studies are difficult to implement in solution, but have been carried out on solid substrates, mostly under specialized conditions, including ultra high vacuum. The present study illustrates the facility with which in situ growth of metal nanoparticles in thin polymer films under ambient conditions can be monitored by real time atomic force microscopy. Formation of silver nanoparticles inside spin-coated thin films of poly(vinylpyrrolidone) containing silver nitrate, under ambient conditions, is revealed by the emergence and growth of surface plasmon resonance absorption extending over several hours. Atomic force microscopy allows 'direct observation' of structures growing near the surface; individual nanostructures can be monitored in the case of very thin films. A plausible mechanism is proposed for the chemical reactions occurring inside the film with the polymer itself acting as the reducing agent leading to the formation and growth of the nanoparticles. The present study opens up new avenues to carry out investigations into the mechanisms and kinetics of nanoparticle growth.

Growth and structural properties of CuAg and CoPt bimetallic nanoparticles

Core/shell CuAg and alloyed CoPt have been synthesized using two vapor phase deposition techniques. For CuAg prepared by Thermal Evaporation (TE), the size and the morphology of the Cu cores are the key parameters to promote the formation of the core/shell arrangement. For CoPt synthesized by Pulsed Laser Deposition (PLD), the growth kinetics of nanoparticles, depending on the deposition rate, the substrate nature and the temperature, controls the nanoparticle morphology. The competition between the growth and the ordering kinetics governs the nanoparticle structure. By reducing the growth kinetics, as-grown L1(0) ordered nanoparticles are obtained according to the bulk phase diagram.