Stable Aqueous Suspensions Research Articles

Polyfunctional Siloxane Water-Soluble Nanoparticles for Biomedical Applications

Hydrolysis of N-methyl-N-(2,3,4,5,6-pentahydroxyhexyl)-N′-(3-triethoxysilylpropyl)urea gave water-soluble polysiloxane nanoparticles. They can be used for the preparation of intensely luminescent stable aqueous suspensions of water-insoluble or poorly soluble compounds (Eu(BTFA)3 · 6H2O complex and tetracyano-tetraaryl-porphyrazines) for biomedical applications, in particular, for bioimaging.

A facile method to functionalize gold nano-tripods with high suspension stability in an aqueous environment.

Here we aim to develop a facile emulsion-based method to prepare tripod gold nanoparticles (AuNPs) with high suspension stability in an aqueous environment. A gyroid-structured polymer template formed by the hydrolysis of a degradable block copolymer, polystyrene (PS)-b-poly(l-lactide), is used for the fabrication of AuNPs. Also, a successful emulsification of dichloromethane (DCM) in the aqueous phase is developed by using thiolated polyethylene glycol (PEG-SH) as the stabilizer. Subsequently, the nanohybrids of PS/Au can be fabricated by templated electroless plating, and then selectively dissolving in the DCM dispersive phase. Most interestingly, a dedicated process for the simultaneous release of the tripod AuNPs from the dissolution of PS associated with PEG-SH at the interface of the emulsion is achieved, giving PEG-SH-functionalized tripod AuNPs dispersed in the aqueous phase, which significantly improves the suspension stabilization of tripod AuNPs. The in situ temperature-programmed electrospray-differential mobility analysis provides a quantitative, statistical analysis of mobility diameter, dynamic shape factor, polydispersity, and colloidal stability.

Ilex paraguariensis Extract-Coated Magnetite Nanoparticles: A Sustainable Nano-adsorbent and Antioxidant

Single-crystal 15 nm size magnetite nanoparticles were synthesized and coated with Yerba Mate (Ilex paraguariensis) extract to evaluate their use as versatile antioxidant magnetic nanoadsorbents. The obtained particles, Mnp@YM, were found to be composed of a crystalline magnetite core surrounded by a shell composed of Fe3O4, FeO, and Fe2O3 oxides. YM extract resulted an effective protective coating for Mnp incorporating surface carboxylates, phenols, and organic N groups which improve the particles stability in aqueous suspensions. Mnp@YM antioxidant capacity (1.8 µM Trolox equivalent per 0.1 mg YM coating contained in 1 mgL− 1 particle suspension) is of the order reported for polyphenols. $${\text{S}}{{\text{O}}_{\text{4}}}^{{ \cdot - }}$$ scavenging rate constant (1.5 × 104 g− 1 L s− 1) is within the diffusion controlled regime for 15 nm spherical nanoparticles with homogeneously distributed reactive sites. Mnp@YM reversibly adsorbs MB with maximum adsorption of 50 mg g− 1. As a consequence of these capacities, Mnp@YM resulted effective in preventing MB oxidation by peroxodisulfate.

Light refraction in aqueous suspensions of diamond particles

In this paper the results of research of the influence of particle size and material in aqueous suspensions of diamond particles which included both diamond and graphite on suspension refractive index are presented. Eight fractions of nanodiamond were isolated using particle sedimentation and dilute suspensions were characterized using dynamic light scattering (DLS) method and electro-optical method. The increment of suspension refractive index was determined using diffraction, refraction, and reflection. Theoretical calculations of the dependence of refractive index increment of suspensions on the radius of diamond and graphite particles of spherical shape were carried out. The applicability of this approximation was supported by static light scattering experimental data. By comparing theoretical and experimental values of the increment of the refractive index it was possible to conclude that both diamond and graphite is present in the dispersed phase. It was shown that the removal of large particles from suspensions by centrifugation has little effect on its refractive index, but significantly reduces turbidity. It was demonstrated that particle aggregation leads to a decrease of the suspension refractive index, which can be used for express analysis of stability of aqueous suspensions of diamond particles.

Layered double hydroxide using hydrothermal treatment: morphology evolution, intercalation and release kinetics of diclofenac sodium

The present work demonstrates the possibilities of hydrothermal transformation of Zn-Al layered double hydroxide (LDH) nanostructure by varying the synthetic conditions. The manipulation in washing step before hydrothermal treatment allows control over crystal morphologies, size and stability of their aqueous solutions. We examined the crystal growth process in the presence and the absence of extra ions during hydrothermal treatment and its dependence on the drug (diclofenac sodium (Dic-Na)) loading and release processes. Hexagonal plate-like crystals show sustained release with ∼90% of the drug from the matrix in a week, suggesting the applicability of LDH nanohybrids in sustained drug delivery systems. The fits to the release kinetics data indicated the drug release as a diffusion-controlled release process. LDH with rod-like morphology shows excellent colloidal stability in aqueous suspension, as studied by photon correlation spectroscopy.

Structural, magnetic and hyperfine characterization of ZnxFe3–xO4 nanoparticles prepared by sol-gel approach via inorganic precursors

Structural characteristics and magnetic properties of ZnxFe3–xO4 (where х = 0; 0.09; 0.18; 0.45; 1) nanoparticles were studied with X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared spectroscopy (IR) and vibrating sample magnetometry (VSM). Oxidation of Fe2+ ions, redistribution of Zn2+ and Fe3+ ions between octahedral and tetrahedral sites, and the formation of cation vacancies in spinel-type cubic structure of the obtained ZnxFe3–x–y□yO4 substitutional solid solutions were revealed by 57Fe Mössbauer spectroscopy. The nanoparticles synthesized via a modified sol-gel method using inorganic precursors have a size of 4–10 nm, single-phase composition, superparamagnetic behavior at room temperature (300 K) and a relatively hydrophilic surface to form stable aqueous suspensions. The maximum magnetization of 59 emu/g at 300 K corresponds to Zn0.18Fe2.82O4 composition. The listed features make the materials promising candidates for various biological and medical applications such as contrast-enhanced magnetic resonance imaging, hyperthermia of pathological tissues, controlled drug release, and separation of nucleic acids.

Determinant influence of the electrical conductivity versus surface area on the performance of graphene oxide-doped carbon xerogel supercapacitors

A series of resorcinol formaldehyde based carbon xerogels were synthesized under identical conditions using different graphene oxide loads. The gelification reaction was carried out using a stable aqueous suspension of graphene oxide, yielding organic gels with graphene oxide concentrations ranging from 1.2–2.5%. After the carbonization, xerogels with medium surface area (650 m2/g) and a highly improved electrical conductivity were obtained. Specific capacitance of 120 F/g of one electrode at very high scan rate of 500 mV/s were achieved, as well as power densities above 30 kW/kg, which is a significant improvement of 180% with respect to the pristine xerogels. Carbonized xerogels were further steam activated to yield activated carbon xerogels with surface areas of up to 1800 m2/g. The use of activated xerogels improves slightly the specific capacitance at low scan rates only, and there is a sharp decrease above 20 mV/s, resulting in a worse performance than graphene oxide doped carbonized xerogels. The electrical conductivity of the graphene oxide-doped carbon xerogels decreases upon activation, which means that the influence of the electrical conductivity on a carbon xerogel is greater than its specific surface area, which it is the first time it is observed for porous carbons.

Turbidimetric studies of colloidal silica/aqueous solution system stability

The effects of solid content, temperature, supporting electrolyte (sodium chloride (NaCl)) concentration, solution pH, molecular weight of synthetic non-ionic polymer, natural polymer addition and synthetic copolymer presence on the silica suspension stability were examined. The natural proteins – human serum albumin and lysozyme (LSZ) – as well as the exopolysaccharide synthesized by soil bacterium Sinorhizobium meliloti 1021 were used. Moreover, synthetic homopolymers – non-ionic poly(vinylpyrrolidone) and copolymers of polyamino acids with poly(ethylene glycol) – were applied. The turbidimetric method was used to monitor the colloidal silica aqueous suspension stability as a function of time. LSZ and copolymers containing polylysine at the basic values of solution pH have the greatest effect on system destabilization. The negative surface charge neutralization by the positively charged groups of the polymeric chains is mainly responsible for such behavior of the systems under examination. On the other hand, the synthetic polyvinylpyrrolidone causes considerable improvement of silica suspension stability. Its adsorption on the solid particles surface causes efficient stabilization due to steric repulsion occurrence.

Synthesis of silver nanoparticles in the presence of diethylaminoethyl-dextran hydrochloride polymer and their SERS activity

The silver nanoparticles (AgNPs) were synthesized upon γ-irradiation of AgNO3 precursor suspensions in the presence of diethylaminoethyl-dextran hydrochloride (DEAE-dextran) cationic polymer as a stabilizer. The dose rate of γ-irradiation was ~32 kGy h−1, and absorbed doses were 30 and 60 kGy. The γ-irradiation of the precursor suspension at acidic or neutral pH conditions produced predominantly the silver(I) chloride (AgCl) particles, because of the poor solubility of AgCl already present in the precursor suspension. The origin of AgCl in the precursor suspension was due to the presence of chloride ions in DEAE-dextran hydrochloride polymer. The addition of ammonia to the precursor suspension dissolved the AgCl precipitate, and the γ-irradiation of such colourless suspension at alkali pH produced a stable aqueous suspension with rather uniform spherical AgNPs of approximately 30 nm in size. The size of AgNPs was controlled by varying the AgNO3/DEAE-dextran concentration in the suspensions. The surface-enhanced Raman scattering (SERS) activities of synthesized AgNPs were examined using organic molecules rhodamine 6G, pyridine and 4-mercaptobenzoic acid (4-MBA). The NaBH4 was used as SERS aggregation agent. The SERS results have shown that in the presence of synthesized AgNPs, it was possible to detect low concentration of tested compounds.

Shades of red: Comparative study on supercritical CO2 extraction of lycopene-rich oleoresins from gac, tomato and watermelon fruits and effect of the α-cyclodextrin clathrated extracts on cultured lung adenocarcinoma cells’ viability

Lycopene is a red carotenoid thought effective in preventing some types of cancers and modulating immune and inflammatory responses. Though some fruits share the common feature of synthesizing and storing lycopene as main carotenoid within chromoplasts, they significantly differ in the lipophilic phytocomplex. The purpose of this work was: i) to extract solvent-free lycopene-rich oleoresins from gac, tomato and watermelon ripe-fruits by supercritical CO2 suitable for functional food and nutraceutical formulations; ii) characterize the oleoresins with respect to carotenoids, tocochromanols, lipids, metals and antioxidant activity; iii) prepare stable aqueous suspensions through oleoresin clathration into α-cyclodextrins (α-CDs); iv) investigate the effect of each lycopene-containing suspension on viability of human lung adenocarcinoma cells. The results showed that all oleoresins represent a safe added-value source of lycopene characterized by high lipophilic antioxidant activity, improved by the synergy with other biomolecules. Interestingly, when administered at identical concentrations (0.5–10μM) of lycopene, the extracts showed conflicting behaviors: gac and tomato suspensions significantly increased cell viability, whereas watermelon oleoresin/α-CD suspension significantly decreased cell viability. Although further studies are required, this research suggests a fundamental role of phytocomplex in affecting the responses of cancer cell survival to the in vitro administration of lycopene.

Synthesis and characterization of $$\hbox {BaNiO}_{3}$$ BaNiO 3 using a solid-state thermal decomposition method and the preparation of its stable aqueous suspension

In the present study, the preparation of \(\hbox {BaNiO}_{3}\) nano-oxide is reported via simple solid-state thermal decomposition of \([\hbox {Ba(en)}_{4}][\hbox {Ni(H}_{2}\hbox {O})_{2}\hbox {(NCS)}_{4}]\) precursor complex for the first time. As-prepared nano-oxide was coated by citric acid to form a stable aqueous magnetic suspension. The precursor complex was characterized by conductivity measurements, ultra violet–visible spectroscopy, elemental analysis and Fourier transform infrared spectroscopy. The composition of the perovskite was confirmed by energy-dispersive X-ray spectroscopy analysis and the hexagonal structure was supported by powder X-ray diffraction. In addition, monotonous morphology of the nano-oxide was illustrated by field-emission scanning electron microscopy. Superparamagneticity of the nanoparticles were detected using a vibrating sample magnetometer. Finally, the hydrodynamic size as well as the zeta potential of the pristine and surface-treated \(\hbox {BaNiO}_{3}\) nano-oxide were measured in deionized water via a dynamic light scattering analyzer and they were compared. Results show the excellent stability of the surface-modified magnetic oxide compared to the pristine.

Carbon Dots as Nanodispersants for Multiwalled Carbon Nanotubes: Reduced Cytotoxicity and Metal Nanoparticle Functionalization.

The colloidal stabilization of multiwalled carbon nanotubes (MWCNTs) in an aqueous medium through noncovalent interactions has potential benefits toward the practical use of this one-dimensional carbonaceous material for biomedical applications. Here, we report that fluorescent carbon nanodots can efficiently function as dispersing agents in the preparation of stable aqueous suspensions of CNTs at significant concentrations (0.5 mg/mL). The amphiphilic nature of carbon dots with a hydrophobic graphitic core could effectively interact with the CNT surface, whereas hydrophilic oxygenated functionalization on the C-dot surface provided excellent water dispersibility. The resultant CNT-C-dot composite showed significantly reduced cytotoxicity compared to that of unmodified or protein-coated CNTs, as demonstrated by cell viability and proliferation assays. Furthermore, the reducing capability of C-dots could be envisaged toward the formation of a catalytically active metal nanoparticle-CNT-C-dot composite without the addition of any external reducing or stabilizing agents that showed excellent catalytic activity toward the reduction of p-nitrophenol in the presence of NaBH4. Overall, the present work establishes C-dots as an efficient stabilizer for aqueous dispersions of CNTs, leading to an all-carbon nanocomposite that can be useful for different practical applications.

Separation of cellulose nanowhiskers from microcrystalline cellulose with an aqueous protic ionic liquid based on ammonium and hydrogensulphate

Cellulose nanowhiskers (NWC) have several applications, but its achievement, when held by hydrolysis with strong acids, presents some undesirable aspects as their corrosivity, toxicity and low recovery rate. Recently, [BMIM][HSO4] was proposed as an alternative, but its use has yet disadvantages, mainly due its toxicity and cost. In this sense, this work reports the separation of NWC from MCC by a synthetized protic ionic liquid 2-hydroxyethylamonium hydrogensulphate ([2-HEA][HSO4]) potentially lower toxic than [BMIM][HSO4], which can be easily produced by a low-cost procedure. A stable and polydisperse NWC aqueous suspension was formed exhibiting the birefringence flow typical of nanoparticle dispersions. TEM micrographies confirm needle-shape particles with high average aspect ratio of 50.23 ± 20.93 nm. A good thermal stability was achieved, with Tmax of cellulose decomposition around 234 °C. No ionic liquid residues were observed in the NWC by FTIR analysis. The calculated crystallinity index and crystallite size were 54% and 17.2 nm, respectively. The ionic liquid used in the hydrolysis experiments was successfully recovered in 76.91 ± 0.13% yield, with a similar structure to that of the original ionic liquid. Therefore, [2-HEA][HSO4] was successfully tested as a new, alternative and promising medium to separate cellulose nanowhiskers from cellulosic sources.

Stability of aqueous suspensions of alumina particles with adsorbed (carboxymethyl)cellulose

The influence of the counterion condensation on the colloid stability of alumina suspension with added carboxymethylcellulose (CMC) is investigated by electric light scattering and microelectrophoresis. The electrophoretic mobility μ and the interface ion polarizability γ are used as criteria for the effective charge of CMC-alumina particles. The light scattering intensity I0 and the field-strength dependence τ(E2) of the relaxation time τ are used as criteria for aggregation. The polymer-concentration dependences μ(CCMC), γ(CCMC) and I0(CCMC) under and above the recharging point are measured at different degrees of proton dissociation α and fraction φ of counterions condensed on the adsorbed polyelectrolyte chains: α≈1/2, φ=0 at pH 4.5, and α≈1, φ≈1/3 at pH 6.0. The results show out that the colloid stability is conditioned by the effective charge of CMC-alumina particles determined by the surface charge, the dissociated carboxylic groups of CMC chains and the condensed counterions. The particle aggregation about the recharging point (at 1:50 CMC/alumina) is explained with hetero-coagulation by polyelectrolyte chain bridging conditioned by the reduced total charge, surface charge-patches, low surface occupation and the high rigidity of CMC chains.

Magnetoimpedance biosensor prototype for ferrogel detection

Ferrogels are composite materials widely introduced in the area of biomedical engineering as magnetic field sensitive transformers. These biomimetic materials can be prepared by incorporating monodomain magnetic nanoparticles into chemically crosslinked hydrogels. The properties of a biomimetic ferrogels taken for the study unlike that of the biological prototype might be set up by the synthesis and can be thoroughly controlled in a physical experiment. In this work we developed a giant magnetoimpedance sensor with a multilayered FeNi/Ti-based sensitive element adapted for ferrogel studies. Ferrogels were synthesized by radical polymerization of acrylamide in a stable aqueous suspension of γ-Fe2O3 MNPs fabricated by laser target evaporation. The magnetoimpedance measurements in initial state and in the presence of ferrogels with concentrations of nanoparticles from 0 to 2.4wt% in a frequency range of 1–300MHz allowed a precise characterization of the stray fields of the nanoparticles present in the ferrogel.

Mechanochemical synthesis of finite particle of layered double hydroxide-acetate intercalation compound: Swelling, thin film and ion exchange

Acetate intercalated Mg-Al layered double hydroxide was successfully synthesized by the solid-state reactions between magnesium acetate and aluminum hydroxide as the starting materials using a planetary mil. The acetate intercalated Mg-Al layered double hydroxide prepared by the present solid-state reaction was finite particle and was processed into stable aqueous suspension with variable transparency and viscosity depending on the concentration. By drying the suspension on a substrate under nitrogen atmosphere, thin film (with the thickness of several micrometers) of the acetate intercalated Mg-Al layered double hydroxide with the basal plane oriented parallel to the substrate was obtained. The ion exchange ability of the film, which is as an advantage of the acetate form of layered double hydroxide, was shown by the ion exchange with coumarin-3-carboxylate to give a photoluminescent film. The solid-solid reaction is advantageous for the preparation of layered double hydroxides due to the simple and eco-friendly nature (no solvent) of the operation, lower possibility of carbonate contamination and finite particles of the products.

Synthesis, characterization and cytotoxicity of S-nitroso-mercaptosuccinic acid-containing alginate/chitosan nanoparticles

Nitric oxide (NO) is an endogenous free radical, which plays key roles in several biological processes including vasodilation, neurotransmission, inhibition of platelet adhesion, cytotoxicity against pathogens, wound healing, and defense against cancer. Due to the relative instability of NO in vivo (half-life of ca. 0.5 seconds), there is an increasing interest in the development of low molecular weight NO donors, such as S-nitrosothiols (RSNOs), which are able to prolong and preserve the biological activities of NO in vivo. In order to enhance the sustained NO release in several biomedical applications, RSNOs have been successfully allied to nanomaterials. In this context, this work describes the synthesis and characterization of the NO donor S-nitroso-mercaptosuccinic acid (S-nitroso-MSA), which belongs to the class of RSNOs, and its incorporation in polymeric biodegradable nanoparticles composed by alginate/chitosan. First, chitosan nanoparticles were obtained by gelation process with sodium tripolyphosphate (TPP), followed by the addition of the alginate layer, to enhance the nanoparticle protection. The obtained nanoparticles presented a hydrodynamic diameter of 343 ± 38 nm, polydispersity index (PDI) of 0.36 ± 0.1, and zeta potential of − 30.3 ± 0.4 mV, indicating their thermal stability in aqueous suspension. The negative zeta potential value was assigned to the presence of alginate chains on the surface of chitosan/TPP nanoparticles. The encapsulation efficiency of the NO donor into the polymeric nanoparticles was found to be 98 ± 0.2%. The high encapsulation efficiency value was attributed to the positive interactions between the NO donor and the polymeric content of the nanoparticles. Kinetics of NO release from the nanoparticles revealed a spontaneous and sustained release of therapeutic amounts of NO, for several hours under physiological temperature. The incubation of NO-releasing alginate/chitosan nanoparticles with human hepatocellular carcinoma (HepG2) cell line revealed a concentration-dependent toxicity. These results point to the promising uses of NO-releasing alginate/chitosan nanoparticles for anti-cancer chemotherapy.

3D multiscale controlled micropatterning of lead-free piezoelectric electroceramics via Epoxy Gel Casting and lift-off

We report on the fabrication of multiscale three-dimensional (3D) micropatterning of 0.5Ba(Zr0.2Ti0.8)O3−0.5(Ba0.7Ca0.3)TiO3 (BZT−BCT) electroceramic material using soft lithographic PDMS moulds. The ceramic microcomponents were successfully consolidated by Epoxy Gel Casting from stable aqueous suspension of BZT-BCT material. A successful aqueous processing of electroceramic material was employed with surface protection of powder particles against hydrolysis as considerably an important parameter to achieve high solid loading suspension with pseudoplastic behaviour suitable for casting in micro scale moulds. The process to obtain micro sized pattern of material was divided in two steps: (i) production of high quality SU-8 master moulds and the respective negative replicas in PDMS (soft mould) by photolithography and soft mould replication, respectively; (ii) casting the soft moulds by stable high solid loading BZT-BCT suspensions in presence of gelation agents followed by de-moulding, drying and sintering. The resulting green micropattern structures show interesting features, including complex structures with a periodic variations through their length and, multiscale array of hexagonal shaped pillars of different aspect ratios (AR) (max AR≈8 with approx ∼320μm of height and side length ∼40μm) with smooth side wall features along height. The green pillar arrays were further sintered to show the suitability of aqueous processing of material and proposed casting method.

Barium Hexaferrite Magnetic Fluid: Preparation, Characterization and the In Vitro Identification of Cytotoxicity and Antibacterial Activity

As an alternative way to encounter antibiotic-resistant strains of bacteria, we report here a harmless magnetic fluid, which can be targeted to infections using external magnetic field and destroy the target. Ultrafine BaFe12O19 nanoparticles were synthesized using the hydrothermal approach; for the first time, the nanoparticles were coated with citric acid to form a stable aqueous suspension. Characterization of the prepared (coated) oxide was performed on Furrier transform infrared spectroscopy (FT-IR), powder X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), dynamic light scattering (DLS), energy-dispersive X-ray spectroscopy (EDS) analysis and vibrating sample magnetometry (VSM). In vitro cytotoxicity, as well as the antibacterial activity of the surface modified nano-oxide, was measured against eukaryotic cells and samples from both Grams of bacterial strains, respectively. The results showed that the superparamagnetic crystals of barium hexaferrite were successfully surface modified to form a water-based stable magnetic fluid. The magnetic fluid measured to be extremely bio compatible by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) test. Disc diffusion and minimum inhibitory concentration (MIC) methods revealed that the surface modified nano-oxide is fetal for both the Gram-negative Escherichia coli (E. coli) and the Gram-positive Staphylococcus aureus (S. aureus). However, the fatality of the nanoparticles is lower for the Staphylococci strain.

Alkaline Delignification of Cactus Fibres for Pulp and Papermaking Applications

Stable aqueous suspensions with high cellulosic contents and low fractions of lignin have been prepared from Cactus fibres via chemical delignification of the Cactus biomass feedstock with a sodium hydroxide–anthraquinone (soda–AQ) mixture. In order to optimize the reaction parameters, various temperatures between 120 and 170 °C and reaction times between 60 and 180 min were examined. The optimal yield of the resulting alkaline pulps (corresponding to the complete reaction of the raw materials) was equal to 41.4%, while the morphological parameters of individual cellulose fibres (such as length, width, and fraction of fine elements) were determined using a MorFi analyser. The estimated degree of polymerization, water retention value, total charge, and drainability of the produced pulps confirmed their suitability for papermaking applications; as a result, paper sheets were manually prepared using a Rapid-Kothen sheet former apparatus. The morphological analysis of the produced paper was conducted using a scanning electron microscopy technique, and its structural and mechanical properties were evaluated with the standard laboratory testing equipment. The obtained results indicate that the paper fabricated from Cactus fibres via the soda–AQ delignification process exhibits homogenous morphology as well as satisfactory mechanical and structural properties.