Term Colloidal Stability Research Articles

Effect of hydrodynamic size on colloidal stability and lifetime of Mn-Zn magnetic fluids

For transformer cooling applications, magnetic particles need to be dispersed in carrier fluids with high colloidal stability for a long period without significant degradation. However, stability of the suspension, especially the long term colloidal stability is a crucial factor for the applications in power transformers because aggregation of particles could cause clogging of micro-channels in transformers. In this article, we have reported effect of hydrodynamic size on the colloidal stability of Mn1-xZnxFe2O4 (MZ) nanoparticles (NPs)–based magnetic fluids. Lifetime of fluids has been determined from the increase in hydrodynamic size of magnetic NPs due to aggregation. Colloidal stability of fluids decreases with increase in the polydispersity of fluids caused by the enhanced dipole interactions between NPs resulting in the aggregation of NPs in chain-like structures.

Feasibility of Electrostatic-Mediated Post-Functionalization to Induce Long Term Colloidal Stability and Stability After Freeze Drying of Amphoteric Nanoparticles

A commercialized iron oxide nanoparticles (of amphoteric nature) were surface modified with poly(sodium 4-styrenesulfonate) (PSS) via a simple electrostatic-mediated post-functionalization technique. The modification is successful if the iron oxide nanoparticles experience a complete alteration in surface properties. Such observation was obtained when the functionalization was conducted at pH 3.5, in which the iron oxide nanoparticles and the PSS molecules were of opposite charge. Here, the PSS can be attached onto the iron oxide via electrostatic attraction. In contrast, poor surface modification was resulted when the functionalization was conducted at pH > 9, in which iron oxide and PSS repulse each other upon having similar surface charge. Later on, the ability of the electrostatic-mediated post-functionalization to continually impose good colloidal stability on the iron oxide nanoparticles for a long period (6 months) and its ability to sustain from lyophilization process were evaluated by tracking the evolution of particle hydrodynamic size.

Unravelling the mechanisms that determine the uptake and metabolism of magnetic single and multicore nanoparticles in a Xenopus laevis model.

Multicore superparamagnetic nanoparticles have been proposed as ideal tools for some biomedical applications because of their high magnetic moment per particle, high specific surface area and long term colloidal stability. Through controlled aggregation and packing of magnetic cores it is possible to obtain not only single-core but also multicore and hollow spheres with internal voids. In this work, we compare toxicological properties of single and multicore nanoparticles. Both types of particles showed moderate in vitro toxicity (MTT assay) tested in Hep G2 (human hepatocellular carcinoma) and Caco-2 (human colorectal adenocarcinoma) cells. The influence of surface chemistry in their biological behavior was also studied after functionalization with O,O'-bis(2-aminoethyl) PEG (2000 Da). For the first time, these nanoparticles were evaluated in a Xenopus laevis model studying their whole organism toxicity and their impact upon iron metabolism. The degree of activation of the metabolic pathway depends on the size and surface charge of the nanoparticles which determine their uptake. The results also highlight the potential of Xenopus laevis model bridging the gap between in vitro cell-based assays and rodent models for toxicity assessment to develop effective nanoparticles for biomedical applications.

Orthogonal analysis of functional gold nanoparticles for biomedical applications.

We report a comprehensive strategy based on implementation of orthogonal measurement techniques to provide critical and verifiable material characteristics for functionalized gold nanoparticles (AuNPs) used in biomedical applications. Samples were analyzed before and after ≈50 months of cold storage (≈4 °C). Biomedical applications require long-term storage at cold temperatures, which could have an impact on AuNP therapeutics. Thiolated polyethylene glycol (SH-PEG)-conjugated AuNPs with different terminal groups (methyl-, carboxylic-, and amine-) were chosen as a model system due to their high relevancy in biomedical applications. Electrospray-differential mobility analysis, asymmetric-flow field flow fractionation, transmission electron microscopy, scanning electron microscopy, atomic force microscopy, inductively coupled plasma mass spectrometry, and small-angle X-ray scattering were employed to provide both complementary and orthogonal information on (1) particle size and size distribution, (2) particle concentrations, (3) molecular conjugation properties (i.e., conformation and surface packing density), and (4) colloidal stability. Results show that SH-PEGs were conjugated on the surface of AuNPs to form a brush-like polymer corona. The surface packing density of SH-PEG was ≈0.42 nm(-2) for the methyl-PEG-SH AuNPs, ≈0.26 nm(-2) for the amine-SH-PEG AuNPs, and ≈0.18 nm(-2) for the carboxylic-PEG-SH AuNPs before cold storage, approximately 10 % of its theoretical maximum value. The conformation of surface-bound SH-PEGs was then estimated to be in an intermediate state between brush-like and random-coiled, based on the measured thicknesses in liquid and in dry states. By analyzing the change in particle size distribution and number concentration in suspension following cold storage, the long term colloidal stability of AuNPs was shown to be significantly improved via functionalization with SH-PEG, especially in the case of methyl-PEG-SH and carboxylic-PEG-SH (i.e., we estimate that >80 % of SH-PEG5K remained on the surface of AuNPs during storage). The work described here provides a generic strategy to track and analyze the material properties of functional AuNPs intended for biomedical applications, and highlights the importance of a multi-technique analysis. The effects of long term storage on the physical state of the particles, and on the stability of the ligand-AuNP conjugates, are employed to demonstrate the capacity of this approach to address critical issues relevant to clinical applications.

Quantitative Replacement of Citrate by Phosphane on Silver Nanoparticle Surfaces Monitored by Surface-Enhanced Raman Spectroscopy (SERS).

Chemical approaches to metal NP synthesis commonly use capping agents to achieve a desired NP size and shape. Frequently, such NPs require chemically different surface ligands after synthesis to generate desired NP properties (e.g., charge or hydrophilicity) and to increase their long term colloidal stability. Here, we prepared SERS active citrate-stabilized silver NPs (d = 38±4 nm), purified them from remaining reactants by ultracentrifugation and redispersion, and immersed them into solutions containing different concentrations of Tris(sodium-m-sulfonatophenyl)phosphine (TPPTS), which is often used in such ligand replacement approaches to increase colloidal stability. After equilibration, SERS spectra were acquired, elucidating the concentration dependence of the ligand replacement reaction. SERS data were complemented by concentration dependent size measurements and relations between ligand exchange and colloidal stability are discussed.

Strategies for interfacing inorganic nanocrystals with biological systems based on polymer-coating.

Interfacing inorganic nanoparticles and biological systems with the aim of developing novel imaging and sensing platforms has generated great interest and much activity. However, the effectiveness of this approach hinges on the ability of the surface ligands to promote water-dispersion of the nanoparticles with long term colloidal stability in buffer media. These surface ligands protect the nanostructures from the harsh biological environment, while allowing coupling to target molecules, which can be biological in nature (e.g., proteins and peptides) or exhibit specific photo-physical characteristics (e.g., a dye or a redox-active molecule). Amphiphilic block polymers have provided researchers with versatile molecular platforms with tunable size, composition and chemical properties. Hence, several groups have developed a wide range of polymers as ligands or micelle capsules to promote the transfer of a variety of inorganic nanomaterials to buffer media (including magnetic nanoparticles and semiconductor nanocrystals) and render them biocompatible. In this review, we first summarize the established synthetic routes to grow high quality nanocrystals of semiconductors, metals and metal oxides. We then provide a critical evaluation of the recent developments in the design, optimization and use of various amphiphilic copolymers to surface functionalize the above nanocrystals, along with the strategies used to conjugate them to target biomolecules. We finally conclude by providing a summary of the most promising applications of these polymer-coated inorganic platforms in sensor design, and imaging of cells and tissues.

Green Synthesis of Curcumin Capped Gold Nanoparticles and Evaluation of Their Cytotoxicity

A green approach to synthesize gold nanoparticles using turmeric rhizome extract, curcumin and curcumin glycoside acting as reducing and stabilizing agents at room temperature is described. The obtained gold nanoparticles were characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). The possible mechanism for the stabilization of nanoparticles is due to the chelation of metal with 1,3-diketone functionality of the curcumin. The gold nanoparticle curcumin hybrids show long term colloidal stability. Furthermore we evaluate the cytotoxic behaviour of curcumin glycoside-Au nanoparticles.

Is the ubiquitous presence of barium carbonate responsible for the poor aqueous processing ability of barium titanate?

Abstract The ubiquitous presence of barium carbonate (BaCO 3 – BC) as an impurity in barium titanate (BaTiO 3 – BT) has been pointed out as the main reason for the well-known difficulties found by many investigators when attempting to process BT powders in aqueous media. Different and controversial arguments have been put forward to justify the observed aqueous processing difficulties of BT, but a satisfactory explanation is still to be found. With this aim, a systematic study was here undertaken to shed further light on the solid/liquid interactions occurring at the surface of BC and BT particles and their impact on the dispersion ability of both powders, separately and mixed in certain proportions. Long term colloidal stability and high solid loadings (60 vol.%) were obtained for BC, while colloidal instability and a lower maximum content of solids (50 vol.%) could be achieved for BT. This responds to the question risen in the title.

On the role of surface composition and curvature on biointerface formation and colloidal stability of nanoparticles in a protein-rich model system

The need for a better understanding of nanoparticle–protein interactions and the mechanisms governing the resulting colloidal stability has been emphasised in recent years. In the present contribution, the short and long term colloidal stability of silica nanoparticles (SNPs) and silica–poly(ethylene glycol) nanohybrids (Sil–PEG) have been scrutinised in a protein model system. Well-defined silica nanoparticles are rapidly covered by bovine serum albumin (BSA) and form small clusters after 20min while large agglomerates are detected after 10h depending on both particle size and nanoparticle–protein ratio. Oppositely, Sil–PEG hybrids present suppressive protein adsorption and enhanced short and long term colloidal stability in protein solution. No critical agglomeration was found for either system in the absence of protein, proving that instability found for SNPs must arise as a consequence of protein adsorption and not to high ionic environment. Analysis of the small angle X-ray scattering (SAXS) structure factor indicates a short-range attractive potential between particles in the silica-BSA system, which is in good agreement with a protein bridging agglomeration mechanism. The results presented here point out the importance of the nanoparticle surface properties on the ability to adsorb proteins and how the induced or depressed adsorption may potentially drive the resulting colloidal stability.

Lead-free 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 powder surface treated against hydrolysis – a key for a successful aqueous processing

The properties of functional ceramics and their performance in industrial applications are strongly affected by the processing treatments. We report on long term stability of aqueous 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–BCT) suspensions. The effects of aging time on pH and on the leaching extents of Ba, Zr and Ca elements were systematically investigated for the naked, and the surface treated particles against hydrolysis. Suspensions with solid loadings (Φ) up to 60 vol%, pseudoplastic flow behaviours and long term colloidal stability could be achieved from the surface treated powder. A fractal dimension (D) of ∼1.97 to 1.98 was estimated for the BZT–BCT suspensions from the yield stress (τy) versus (Φ) dependence, suggesting a reaction limited cluster aggregation (RLCA) type of particle aggregation with a substantial rearrangement occurring in the aggregates under shearing. The maximum solid loading (Φm) ≈ 61 vol% was determined. The concentrated and stable suspensions represent a stride for successful processing of functional BZT–BCT ceramic components via various aqueous colloidal shaping methods (slip casting, gel-casting, etc.) for large scale industrial applications.

Solution phase synthesis of carbon quantum dots as sensitizers for nanocrystalline TiO2solar cells

Carbon quantum dots (CQDs) have recently emerged as viable alternatives to traditional semiconductor quantum dots because of their facile and low cost synthesis, long term colloidal stability, and low environmental and biological toxicity. The compatible surface chemistry, good solubility in polar solvents and extensive optical absorption throughout the visible and near-infrared wavelength regions render CQDs as potentially useful sensitizers for photovoltaic applications. Presented herein is a new strategy for the solution phase synthesis of water-soluble, colloidally stable CQDs and a preliminary exploration of their utilization as sensitizers in nanocrystalline TiO2 based solar cells. Under AM 1.5 illumination, the Voc and FF values reach 380 mV and 64% respectively, achieving a power conversion efficiency of 0.13%.