Stable Colloidal Dispersions Research Articles

Constructing of DNA vectors with controlled nanosize and single dispersion by block copolymer coating gold nanoparticles as template assembly

Synthesized vectors with nanoscale size and stable colloid dispersion are highly desirable for improving gene delivery efficiency. Here, a core-shell template particle was constructed with polyethylene glycol-b-poly1-(3-aminopropyl)-3-(2-methacryloyloxy propylimidazolium bromine) (PEG-b-PAMPImB) coating gold nanoparticles (PEG-b-PAMPImB-@-Au NPs) for loading DNA and delivering in vitro. Data from transmission electron microscopy (TEM) and dynamic light scattering (DLS) suggest that these nanoplexes, by forming an electrostatic complex with DNA at the inner PAMPImB shell, offer steric protection for the outer PEG corona leading to single dispersion and small size. Notably, higher colloid stability and lower cytotoxicity were achieved with these nanoplexes when compared with PAMPImB monolayer-coated gold nanoparticles (Au NPs). Confocal laser scanning microscopy and intracellular trafficking TEM further indicate that the nanoplexes can translocate across the cell membrane and partly enter the nucleus for high efficient expression. Thus, template assembly represents a promising approach to control the size and colloid stability of gene vectors and ensure safety and efficiency of DNA delivery.

Understanding the Dispersive Action of Nanocellulose for Carbon Nanomaterials.

This work aims at understanding the excellent ability of nanocelluloses to disperse carbon nanomaterials (CNs) in aqueous media to form long-term stable colloidal dispersions without the need for chemical functionalization of the CNs or the use of surfactant. These dispersions are useful for composites with high CN content when seeking water-based, efficient, and green pathways for their preparation. To establish a comprehensive understanding of such dispersion mechanism, colloidal characterization of the dispersions has been combined with surface adhesion measurements using colloidal probe atomic force microscopy (AFM) in aqueous media. AFM results based on model surfaces of graphene and nanocellulose further suggest that there is an association between the nanocellulose and the CN. This association is caused by fluctuations of the counterions on the surface of the nanocellulose inducing dipoles in the sp2 carbon lattice surface of the CNs. Furthermore, the charges on the nanocellulose will induce an electrostatic stabilization of the nanocellulose-CN complexes that prevents aggregation. On the basis of this understanding, nanocelluloses with high surface charge density were used to disperse and stabilize carbon nanotubes (CNTs) and reduced graphene oxide particles in water, so that further increases in the dispersion limit of CNTs could be obtained. The dispersion limit reached the value of 75 wt % CNTs and resulted in high electrical conductivity (515 S/cm) and high modulus (14 GPa) of the CNT composite nanopapers.

Electro-responsive polyelectrolyte-coated surfaces.

The anchoring of polymer chains at solid surfaces is an efficient way to modify interfacial properties like the stability and rheology of colloidal dispersions, lubrication and biocompatibility. Polyelectrolytes are good candidates for the building of smart materials, as the polyion chain conformation can often be tuned by manipulation of different physico-chemical variables. However, achieving efficient and reversible control of this process represents an important technological challenge. In this regard, the application of an external electrical stimulus on polyelectrolytes seems to be a convenient control strategy, for several reasons. First, it is relatively easy to apply an electric field to the material with adequate spatiotemporal control. In addition, in contrast to chemically induced changes, the molecular response to a changing electric field occurs relatively quickly. If the system is properly designed, this response can then be used to control the magnitude of surface properties. In this work we discuss the effect of an external electric field on the adhesion and lubrication properties of several polyelectrolyte-coated surfaces. The influence of the applied field is investigated at different pH and salt conditions, as the polyelectrolyte conformation is sensitive to these variables. We show that it is possible to fine tune friction and adhesion using relatively low applied fields.

Magnetic nanoparticles coated with cyclodextrins and citrate for irinotecan delivery

In the present work, we study the role of different components in the formation of more stable iron oxide magnetic nanoparticles (MNPs): β-cyclodextrin (BCD), 2-hydroxypropyl-β-cyclodextrin (HP) and citrate anion. MNPs formulations were characterized by FTIR, particles size measurements, zeta potential based on dynamic light scattering principle technique, X-ray powder pattern diffraction, XPS spectroscopy, transmission electron microscopy and thermogravimetric analysis. The results showed that cyclodextrins and citrate plays a key role in order to obtain a lower size of coated MNPs and proved to be an efficient strategy to obtain a more stable colloidal dispersion, avoiding the nanoparticles oxidation, enhancing the irinotecan incorporation and release. Furthermore, citrate-coated BCD-MNPs showed the same cytotoxicity of the free IRI.

Cationic functionalized biocompatible polylactide nanoparticles for slow release of proteins

In this study, the formation and structural features of distinct bovine serum albumin (BSA)−loaded cationic-functionalized poly (lactic acid) (PLA) nanoparticles were established and monitored for potential use in the medical and biotechnological applications. The PLA nanoparticles (NPs) produced by low energy solvent displacement were functionalized with the cationic agent hyperbranched polyethylenimine (PEI) for the protein adsorption. The interaction of the BSA with NPs was monitored using zeta potential, dynamic light scattering, atomic force microscopy (AFM) images, Fourier transform infrared spectroscopy and gel electrophoresis for assuring stable colloidal dispersions with mean diameter ranging of 100 to 190nm, and high protein loading efficiency (PLE>80%). The cationic NPs containing PLA:BSA ratio of 1:1w/w stabilized with sorbitan monooleate and poly (vinyl alcohol) exhibited PLE% of 83.2±3.3 and 76.2±0.3 respectively. The slow protein release in these two formulations was diffusion-controlled dependent on BSA/PLA ratio, (Mt/M∞)/t=Kp t −0.5, with release rate constant of Kp=0.127 and Kp=0.110 respectively. The desired biocompability was dependent on PEI/PLA ratio. However, only the formulations stabilized with poly (vinyl alcohol) remained stable over than seven weeks. The data discussed in this approach demonstrated a scaffold of a low energy method for producing small−sized, spherical, stable, and cationic functionalized biodegradable and biocompatible nanoparticles as promising nanocarriers for proteins or negatively charged molecules from the biotechnology source.

Study on the stability of hybrid dispersions of cellulose nanocrystals and aluminum oxide

Hybrid dispersion systems based on cellulose nanocrystals (CNC) and aluminum oxide have been prepared, and the influence of the ζ-potential on their stability has been studied for a wide range of the concentration ratio of the components. Their influence on the morphology and properties of the hybrid particles is evaluated. It is established that one can obtain stable colloidal dispersions with both negatively and positively charged particles or hybrid systems with a neutralized surface charge by controlling the surface potential.

Self-Assembly Behavior of Ultrahighly Charged Amphiphilic Polyelectrolyte on Solid Surfaces.

The adsorption process of a geminized amphiphilic polyelectrolyte, comprising double elementary charges and double hydrophobic tails in each repeat unit (denoted as PAGC8), was investigated and characterized by means of quartz crystal microbalance with dissipation (QCM-D), ellipsometry, and atomic force microscopy (AFM). By comparison, the self-assembly behaviors of a traditional polyelectrolyte without hydrophobic chains (denoted as PASC1) and an amphiphilic polyelectrolyte with a single hydrophilic headgroup and hydrophobic tail in each repeat unit (denoted as PASC8) at the solid/liquid interface were also investigated in parallel. A two-regime buildup was found in both amphiphilic systems of PASC8 and PAGC8, where the first regime was dependent on electrostatic interactions between polyelectrolytes and oppositely charged substrates, and the rearrangements of the preadsorbed chains and their aggregation behaviors on surface dominated the second regime. Furthermore, it was found that the adsorbed amount and conformation changed as a function of the charge density and bulk concentrations of the polyelectrolytes. The comparison of the adsorbed mass obtained from QCM-D and ellipsometry allowed calculating the coupling water content which reached high values and indicated a flexible aggregate conformation in the presence of PAGC8, resulting in controlling the suspension stability even at an extremely low concentration. In order to provide an insight into the mechanism of the suspension stability of colloidal dispersions, we gave a further explanation with respect to the interactions between surfaces in the presence of the geminized polyelectrolyte.

Ultrafine particles in ground sulfide ores: A comparison of four Cu-Ni ores from Siberia, Russia

Nano-, submicro- and micrometer mineral particles may have an important role in beneficiation of metal ores and environmental impact, but their origin and characteristics are poorly understood. Here, we report data for the yield and the composition of fine fractions, and surfaces of several ground Cu-Ni sulfide ores studied using laser diffraction, scanning electron microscopy and energy dispersive X-ray analysis, X-ray photoelectron spectroscopy. Colloidal particles were characterized using dynamic light scattering, zeta-potential measurement, transmission electron microscopy and electron diffraction. The production of fines by dry milling was found to increase from about 0.01vol.% to 0.2vol.% for submicrometer particles and from ~0.5vol.% to about 1.5vol.% for particulate material less than 5μm in the following order: Noril'sk disseminated low sulfide ore≤Noril'sk Cu-rich sulfide ore<Noril'sk valleriite ore<Kingash ore. For wet milling, the yield may be several times higher. Both surfaces of the milled ores and colloids were enriched in O, Mg, Si (largely as serpentine slimes) and depleted in sulfur, basic metals and iron, but colloidal valleriite, chalcopyrite, and oxidized pyrrhotite were found in the respective supernatants too. Typically, the colloidal particles form aggregates with an average hydrodynamic diameter of about 1μm and a smaller number of ~5μm species, except for valleriite ore, which exhibits a single size distribution peak at 2.7μm. Zeta-potential, which characterizes the electric charge of the particles and dispersion stability of colloids, changed from −25mV for the low sulfide ore to about 0mV for valleriite ore, and to +15mV for Kingash ore. Poor flotation recovery of metal from Kingash ore and Noril'sk valleriite ore is suggested to be due to both the large quantities and positive charge of hydrophilic ultrafine serpentine and/or magnesium hydroxide minerals. Resistance to oxidation and hence stability against aggregation of copper-bearing sulfide colloids in waste waters is expected to result in a negative impact on the environment.

Colloids of polypyrrole nanotubes/nanorods: A promising conducting ink

Stable colloidal dispersions of polypyrrole (PPy) nanotubes/nanorods were obtained by the chemical polymerization of pyrrole in the presence of methyl orange and poly(N‐vinypyrrolidone). Due to extended morphology of colloidal particles, the films deposited from colloids with PPy nanotubes/nanorods had conductivity two orders of magnitudes higher than those from colloids of ordinary PPy nanoglobules. Dynamic light scattering measurement demonstrated that PPy nanotubes/nanorods have average particles sizes around 500nm with a dispersity index around 0.3. The PPy colloids were stored over 3 months without visible agglomeration or precipitation. UV–vis spectra of PPy nanotubes/nanorods were recorded both in acidic or alkaline media. Raman spectra excited with 785nm excitation laser confirmed the same mechanism of protonation of nanoglobular and nanotubular PPy. The colloid of PPy nanotubes/nanorods also exhibited good electrochemical redox activity, which makes them promising for the deposition of thin conducting layers used in sensors or energy-storage devices. The dispersions were used for the coating of films on poly(ethylene terephthalate) foils.

Stable and Biocompatible Colloidal Dispersions of Superparamagnetic Iron Oxide Nanoparticles with Minimum Aggregation for Biomedical Applications

In this article, a simple and scalable method for preparing well-defined and highly stable colloidal dispersions of superparamagnetic iron oxide nanoparticles (IONPs) is reported. The IONPs with narrow size distribution were synthesized by polyol process. Nonhazardous sodium tripolyphosphate (STPP) was immobilized on the surface of IONPs via effective ligand exchange in aqueous phase. Then the STPP-capped IONPs were purified by tangential flow ultrafitration. The polyanionic nature of STPP and its strong coordination capability to iron oxide warrant the IONPs long-term colloidal stability even in phosphate-buffer saline. Because the ligand exchange and purification process did not involve repeated precipitation by organic solvents, the unwanted irreversible aggregation and organic impurities were avoided to the utmost extent. The absence of aggregation renders the IONPs well-defined magnetic behaviors and optimized relaxometric properties for T1-weighted magnetic resonance imaging. The in vitro cytotoxici...

Preparation of fullerene С60 dispersions in water

Stable colloidal dispersions of fullerene С60 in water free of organic solvents have been obtained. The addition of a С60 solution to a water–acetone mixture has been shown to cause a solvatochromic effect.

Influence of the synthesis conditions of gold nanoparticles on the structure and architectonics of dipeptide composites

A wide variety of peptides and their natural ability to self-assemble makes them very promising candidates for the fabrication of solid-state devices based on nano- and mesocrystals. In this work, we demonstrate an approach to form peptide composite layers with gold nanoparticles through in situ reduction of chloroauric acid trihydrate by dipeptide and/or dipeptide/formaldehyde mixture in the presence of potassium carbonate at different ratios of components. Appropriate composition of components for the synthesis of highly stable gold colloidal dispersion with particle size of 34–36 nm in dipeptide/formaldehyde solution is formulated. Infrared spectroscopy results indicate that dipeptide participates in the reduction process, conjugation with gold nanoparticles and the self-assembly in 2D, which accompanied by changing peptide chain conformations. The structure and morphology of the peptide composite solid layers with gold nanoparticles on gold, mica and silica surfaces are characterized by atomic force microscopy. In these experiments, the flat particles, dendrites, chains, mesocrystals and Janus particles are observed depending on the solution composition and the substrate/interface used. The latter aspect is studied on the molecular level using computer simulations of individual peptide chains on gold, mica and silica surfaces.

Microgel Surface Modification with Self-Assembling Peptides

We describe the fabrication of peptide-coated microgels, where a fibrillizing peptide (RADA)4 self-assembles on the surface of hydrogel microparticles. The incorporation of an anionic comonomer into the microgel network is required for a stable colloidal dispersion to be obtained when particles are incubated with (RADA)4, suggesting that the assembly is dependent on Coulombic interactions. We further demonstrate the modification of the (RADA)4 shell by preparing coassemblies of (RADA)4 and a fluorescently labeled (RADA)4 peptide. Additionally, the (RADA)4 shell can be modified through postassembly conjugation of a cysteine residue or a non-natural amino acid bearing an alkyne moiety. Fluorescence and atomic force microscopy and circular dichroism spectroscopy were employed to characterize the assembly and modification of the peptide shell. Finally, our attempt to utilize a different fibrillizing peptide (Q11) in the formation of peptide-coated microgels was unsuccessful, demonstrating that the identity of the building blocks is important in the fabrication of these composite assemblies.

Three-dimensional Inkjet Printed Solid Oxide Electrochemical Reactors. I. Yttria-stabilized Zirconia Electrolyte

Solid oxide fuel cell (SOFC) and electrolyser (SOE) performances can be enhanced significantly by increasing the densities of (electrode | electrolyte | pore) triple phase boundaries and improving geometric reproducibility and control over composite electrode | electrolyte microstructures, thereby also aiding predictive performance modelling. We developed stable aqueous colloidal dispersions of yttria-stabilized zirconia (YSZ), a common SOFC electrolyte material, and used them to fabricate 2D planar and highly-customisable 3D microstructures by inkjet printing. The effects of solids fraction, particle size, and binder concentration on structures were investigated, and crack-free, non-porous electrolyte planes were obtained by tailoring particle size and minimising binder concentration. Micro-pillar arrays and square lattices were printed with the optimised ink composition, and a minimum feature size of 35μm was achieved in sintered structures, the smallest published to-date. YSZ particles were printed and sintered to a 23μm thick planar electrolyte in a Ni-YSZ|YSZ|YSZ-LSM|LSM electrolyser for CO2 splitting; a feed of 9:1 CO2:CO mixture at 1.5V and 809°C produced a current density of −0.78 A cm−2 even without more complex 3D electrode | electrolyte geometries.

Development of tannic acid cross-linked hollow zein nanoparticles as potential oral delivery vehicles for curcumin

Sodium carbonate was proposed as a sacrifice template and tannic acid was used as a natural cross-linker to prepare hollow zein nanoparticles (HZN/T). The formulation of nanoparticles, including the amount of water, zein and sodium carbonate, were optimized by surface response methodology (Box-Behnken design). The optimized HZN/T exhibited a small dimension of 87.93 nm with a PDI of only 0.105 and a zeta potential of −39.70 mV, indicating the nanoparticles were homogenous and formed stable colloidal dispersion. Then curcumin was used as a model lipophilic nutrient to explore the encapsulation and delivery potentials of HZN/T, in comparison with hollow zein nanoparticles without tannic acid (HZN/NT) and solid zein nanoparticles with tannic acid (SZN/T) prepared under the same conditions. Generally, the encapsulation efficiency of HZN/T or HZN/NT was significantly higher than that of SZN/T. Interestingly, encapsulation of curcumin dramatically increased particle size of SZN/T by 50 nm, while it did not induce any expansion of the dimension of HZN/T due to its hollow structure. The molecular interactions between curcumin and zein nanoparticles were investigated by Fourier transform infrared spectroscopy and fluorescent spectrophotometer. The in vitro stability and release profile of nanoparticles were evaluated under the simulated gastrointestinal conditions. Although all types of zein nanoparticles showed a sustained release of curcumin, cross-linking via tannic acid played an important role to make zein nanoparticles more resistant against simulated intestinal digestion. Therefore, compared with traditional SZN/T, the HZN/T developed in this study has promising features as a potential oral delivery system for lipophilic nutrients/drugs.

CdSe Nanoplatelets: Living Polymers

AbstractColloidal CdSe nanoplatelets are considered to be excellent candidates for many applications in nanotechnology. One of the current challenges is to self‐assemble these colloidal quantum wells into large ordered structures to control their collective optical properties. We describe a simple and robust procedure to achieve controlled face‐to‐face self‐assembly of CdSe nanoplatelets into micron‐long polymer‐like threads made of up to ∼1000 particles. These structures are formed by addition of oleic acid to a stable colloidal dispersion of platelets, followed by slow drying and re‐dispersion. We could control the average length of the CdSe nanoplatelet threads by varying the amount of added oleic acid. These 1‐dimensional structures are flexible and feature a “living polymer” character because threads of a given length can be further grown through the addition of supplementary nanoplatelets at their reactive ends.

CdSe Nanoplatelets: Living Polymers.

Colloidal CdSe nanoplatelets are considered to be excellent candidates for many applications in nanotechnology. One of the current challenges is to self-assemble these colloidal quantum wells into large ordered structures to control their collective optical properties. We describe a simple and robust procedure to achieve controlled face-to-face self-assembly of CdSe nanoplatelets into micron-long polymer-like threads made of up to ∼1000 particles. These structures are formed by addition of oleic acid to a stable colloidal dispersion of platelets, followed by slow drying and re-dispersion. We could control the average length of the CdSe nanoplatelet threads by varying the amount of added oleic acid. These 1-dimensional structures are flexible and feature a "living polymer" character because threads of a given length can be further grown through the addition of supplementary nanoplatelets at their reactive ends.

Biogenic SiO2 in colloidal dispersions via ball milling and ultrasonication

Biogenic silica from Equisetum arvense was dispersed in aqueous media by using ball milling, high-energy planetary ball milling and ultrasonication. Zeta potential (ζ), dynamic light scattering, and transmission electron microscopy revealed the electrostatic charge and morphological characteristics of the particles, which formed stable colloidal dispersions. Ball milling and ultrasonication yielded particles of 10nm in size that clustered into larger structures. Extended milling time was effective in reducing the particle size by ball milling and ultrasonication but not by high-energy planetary ball milling. The colloidal stability of the dispersions was maximized under alkaline conditions (ζ>−30mV and smallest cluster size of 100–200nm).

Phytochemical Studies on Linum Usitatissimum Seeds and the Nanoformulation of the Bioactive Butanol Extract

The phytochemical investigation of Linum usitatissimum, family Linaceae, resulted in the separation and identification of a lignane, 8–5' neolignan 1 (dehydrodiconiferyl alcohol-4-β-D-glucoside), in addition to identification of many compounds by the GC/MS technique. The antimicrobial activities of hexane, methylene chloride and butanol fractions were comparable to ampicillin. The activities against E. coli were 29.2%, 37.5%, and 66.7%, respectively; against S. aureus were 45.4%, 36.4% and 63.6%, respectively, and against C. albicans were 26.9%, 46.1% and 73.1%, respectively. Antioxidant activity was assessed by ABTS method. It decreased in the following order: ascorbic acid > butanol fraction > methylene chloride fraction > hexane fraction. The cytotoxicity against HePG2 was found to be “moderate” for butanol and methylene chloride fractions, and “weak” for the hexane fraction. The cytotoxicity against MCF-7 was found to be “strong” for butanol fraction, and “weak” for both hexane and methylene chloride fractions. The lignane-rich subfraction, Lu 3d was incorporated into pluronic nano-micelles using nanoprecipitation technique through a modified procedure. The physicochemical characteristics of the developed Lu 3d-loaded nano-micelles such as particle size, potential and morphology were determined using DLS and HR-TEM. The average diameters of the prepared plain and Lu 3d-loaded pluronic nano-micelles were found to be 207 ± 12 and 225 ± 18 nm, respectively. The encapsulation of Lu 3d into nano-sized particles has enhanced their aqueous dissolution and consequently improved their bioavailability. Nanoformulation of Lu 3d led also to a stable colloidal dispersion with a strong green color, indicating its homogenous distribution in the aqueous medium at a significantly higher concentration than that obtained using other solvents.

Lysine-functionalized nanodiamonds as gene carriers: development of stable colloidal dispersion for in vitro cellular uptake studies and siRNA delivery application.

PurposeNanodiamonds (NDs) are emerging as an attractive tool for gene therapeutics. To reach their full potential for biological application, NDs should maintain their colloidal stability in biological milieu. This study describes the behavior of lysine-functionalized ND (lys-ND) in various dispersion media, with an aim to limit aggregation and improve the colloidal stability of ND-gene complexes called diamoplexes. Furthermore, cellular and macromolecular interactions of lys-NDs are also analyzed in vitro to establish the understanding of ND-mediated gene transfer in cells.Methodslys-NDs were synthesized earlier through covalent conjugation of lysine amino acid to carboxylated NDs surface generated through re-oxidation in strong oxidizing acids. In this study, dispersions of lys-NDs were prepared in various media, and the degree of sedimentation was monitored for 72 hours. Particle size distributions and zeta potential measurements were performed for a period of 25 days to characterize the physicochemical stability of lys-NDs in the medium. The interaction profile of lys-NDs with fetal bovine serum showed formation of a protein corona, which was evaluated by size and charge distribution measurements. Uptake of lys-NDs in cervical cancer cells was analyzed by scanning transmission X-ray microscopy, flow cytometry, and confocal microscopy. Cellular uptake of diamoplexes (complex of lys-NDs with small interfering RNA) was also analyzed using flow cytometry.ResultsAqueous dispersion of lys-NDs showed minimum sedimentation and remained stable over a period of 25 days. Size distributions showed good stability, remaining under 100 nm throughout the testing period. A positive zeta potential of >+20 mV indicated a preservation of surface charges. Size distribution and zeta potential changed for lys-NDs after incubation with blood serum, suggesting an interaction with biomolecules, mainly proteins, and a possible formation of a protein corona. Cellular internalization of lys-NDs was confirmed by various techniques such as confocal microscopy, soft X-ray spectroscopy, and flow cytometry.ConclusionThis study establishes that dispersion of lys-NDs in aqueous medium maintains long-term stability and also provides evidence that lysine functionalization enables NDs to interact effectively with the biological system to be used for RNAi therapeutics.