Colloidal Solutions In Water Research Articles

Water dispersible LiNdP4O12 nanocrystals: New multifunctional NIR–NIR luminescent materials for bio-applications

The synthesis and luminescent properties of water colloidal solution of LiNdP4O12 nanocrystals were presented together with demonstrations of their suitability for bio-imaging, remote nano-thermometry and hyperthermal therapy bio-applications. Due to efficient and photostable luminescence at 860nm under ~808nm excitation, NPs luminescence was measured in chicken breast at down to 30mm depths. Moreover temperature dependent spectroscopic features were used in order to remotely measure the temperature of the local environment. Simultaneously, the most heavily Nd3+ doped NCs demonstrated intentional heating – under 1.5W of excitation power at 800nm, local 60K photo-induced temperature rise was observed. The experimental confirmation of bioimaging of LiNdP4O12 nanoparticles in HEK was presented.

Backward-facing step heat transfer of the turbulent regime for functionalized graphene nanoplatelets based water–ethylene glycol nanofluids

Herein, an experimental study on thermo-physical properties of ethylene glycol-functionalized graphene nanoplatelets/water–ethylene glycol nanofluids (EGGNP-WEG) and a numerical study on the convective heat transfer over a backward-facing step are performed. Accordingly, EGGNP was first synthesized covalently to achieve a stable colloidal solution in water–ethylene glycol mixture. Some characterizations were applied to analyze the surface functionality and morphology of EGGNP-flakes. To study the convective heat transfer coefficient in turbulent regime, a numerical study is performed at different weight fractions of EGGNP.According to the results, a higher weight concentration of EGGNP in basefluid indicates a greater extent of convective heat transfer coefficient and thermal conductivity, implying higher heat transfer rate over a backward-facing step.

Water dispersible CoFe2O4 nanoparticles with improved colloidal stability for biomedical applications

Single phase cobalt ferrite (CoFe2O4, CFO) nanoparticles of a controlled size (∼6nm) exhibiting superparamagnetic properties have been synthesized by hydrothermal technique using oleic acid (OA) as surfactant. The oleic acid coated CFO nanoparticles are stable in non-polar organic media, such as hexane but are not well dispersible in water. The surface of these nanoparticles has been further modified by citric acid using ligand exchange process, which makes CFO nanoparticles more stable colloidal solution in water. Citric acid coated CFO nanoparticles exhibits high dispersibility in water, high zeta potential, very low coercivity and moderate saturation magnetization. Biocompatibility of these CFO nanoparticles is demonstrated through cytotoxicity test in L929 cell line.

Light-Induced Heating of Gold Nanoparticles in Colloidal Solution: Dependence on Detuning from Surface Plasmon Resonance

The absorption of light by gold nanoparticles in colloidal water solution has been studied at the simultaneous illumination of nanoparticles by the continuous wave laser beam in dependence on the detuning of laser frequency from the surface plasmon resonance. The appreciable blue shift, broadening, and increase of intensity of the plasmonic absorption band have been observed at approaching of the laser frequency to surface plasmon resonance in Au nanoparticles. The plasmon band broadening reveals the heating of gold nanoparticles that has an evident resonant character. The strong increase of nanoparticle temperature of 316 K has been obtained at moderate laser intensity of 5 × 103 W/cm2 and detuning of 28.5 nm. The sharp blue shift of plasmon band was observed when the temperature exceeded the water boiling point. Such effect is probably due to formation of the vapor bubbles around the Au nanoparticles occurring at water boiling.

Lorentz Friction for Surface Plasmons in Metallic Nanospheres

The Lorentz friction for surface plasmons in metallic nanospheres has been analyzed versus nanoparticle size upon random-phase approximation quasiclassical method. An accurate inclusion of the Lorentz friction to the plasmon damping has been performed. Total attenuation of surface plasmons in a metallic nanosphere has been calculated and minimized with respect to the radius of the nanosphere. Experimentally measured anomalous red-shift of plasmon resonance frequency, increasing with the metallic particle radius growth, especially pronounced for a large size limit, was explained in agreement with the experimental data for Au nanospheres of radii 10–75 nm (the measured quantity being the extinction of the light trans-passing through the water colloidal solution of metallic nanospheres with various radii). A very good agreement of the measured data and the theory with properly included Lorentz friction has been achieved.

Magnetic nanoparticles with high specific absorption rate of electromagnetic energy at low field strength for hyperthermia therapy.

Magnetic nanoparticles (MNPs), referred to as the Dartmouth MNPs, which exhibit high specific absorption rate at low applied field strength have been developed for hyperthermia therapy applications. The MNPs consist of small (2-5 nm) single crystals of gamma-Fe2O3 with saccharide chains implanted in their crystalline structure, forming 20-40 nm flower-like aggregates with a hydrodynamic diameter of 110-120 nm. The MNPs form stable (>12 months) colloidal solutions in water and exhibit no hysteresis under an applied quasistatic magnetic field, and produce a significant amount of heat at field strengths as low as 100 Oe at 99-164 kHz. The MNP heating mechanisms under an alternating magnetic field (AMF) are discussed and analyzed quantitatively based on (a) the calculated multi-scale MNP interactions obtained using a three dimensional numerical model called the method of auxiliary sources, (b) measured MNP frequency spectra, and (c) quantified MNP friction losses based on magneto-viscous theory. The frequency responses and hysteresis curves of the Dartmouth MNPs are measured and compared to the modeled data. The specific absorption rate of the particles is measured at various AMF strengths and frequencies, and compared to commercially available MNPs. The comparisons demonstrate the superior heating properties of the Dartmouth MNPs at low field strengths (<250 Oe). This may extend MNP hyperthermia therapy to deeper tumors that were previously non-viable targets, potentially enabling the treatment of some of the most difficult cancers, such as pancreatic and rectal cancers, without damaging normal tissue.

Towards MRI T2 contrast agents of increased efficiency

Magnetic nanoparticles can be efficient contrast agents for T2 weighted magnetic resonance imaging (MRI) after tuning of some key parameters such as size, surface state, colloidal stability and magnetization, thus motivating the development of new synthetic pathways. In this paper we report the effects of surface coating on the efficiency of two different types of iron based nanoparticles (NPs) as MRI contrast agents. Starting from well-defined hydrophobic iron oxide nanospheres and iron nanocubes of 13 nm size, we have used three methods to increase their hydrophilicity and transfer them into water: surface ligand modification, ligand exchange or encapsulation. The NPs obtained have been characterized by dynamic light scattering and transmission electron microscopy, and the relaxivities of their stable colloidal solutions in water have been determined. Among all samples prepared, iron nanocubes coated by silica display the highest relaxivity (r2) value: 628 s−1 mM−1.

Functional PEG-PAMAM-tetraphosphonate capped NaLnF₄ nanoparticles and their colloidal stability in phosphate buffer.

Developing surface coatings for NaLnF4 nanoparticles (NPs) that provide long-term stability in solutions containing competitive ions such as phosphate remains challenging. An amine-functional polyamidoamine tetraphosphonate (NH2-PAMAM-4P) as a multidentate ligand for these NPs has been synthesized and characterized as a ligand for the surface of NaGdF4 and NaTbF4 nanoparticles. A two-step ligand exchange protocol was developed for introduction of the NH2-PAMAM-4P ligand on oleate-capped NaLnF4 NPs. The NPs were first treated with methoxy-poly(ethylene glycol)-monophosphoric acid (Mn = 750) in tetrahydrofuran. The mPEG750-OPO3-capped NPs were stable colloidal solutions in water, where they could be ligand-exchanged with NH2-PAMAM-4P. The surface amine groups on the NPs were available for derivatization to attach methoxy-PEG (Mn = 2000) and biotin-terminated PEG (Mn = 2000) chains. The surface coverage of ligands on the NPs was examined by thermal gravimetric analysis, and by a HABA analysis for biotin-containing NPs. Colloidal stability of the NPs was examined by dynamic light scattering. NaGdF4 and NaTbF4 NPs capped with mPEG2000–PAMAM-4P showed colloidal stability in DI water and in phosphate buffer (10 mM, pH 7.4). A direct comparison with NaTbF4 NPs capped with a mPEG2000-lysine-based tetradentate ligand that we reported previously (Langmuir2012, 28, 12861−1287022906305) showed that both ligands provided long-term stability in phosphate buffer, but that the lysine-based ligand provided better stability in phosphate-buffered saline.

Colloidal activated carbon and carbon-iron-novel materials for in-situ groundwater treatment

Two novel materials have been developed and tested in initial studies for the in-situ generation of sorption and reactive barriers for subsurface water treatment at low cost by introducing sorbents or reagents via injection wells. Both materials are based on finely-ground activated carbon with a particle size of D50 = 0.8 μm which is quasi-soluble, i.e. it forms stable colloidal solutions in water over a wide concentration range. With these activated carbon colloids, an approved material of environmental technology is now applicable for injection into contaminated aquifers to form sorption barriers by controlled deposition on aquifer sediment directly in the flow passages. A new remediation strategy can be followed – the in-situ generation of a permeable AC sorption barrier in contaminated aquifers. Based on the colloidal carbon particles, a second material has been developed which combines the sorption properties of the activated carbon carrier and the reactivity of the zerovalent iron deposits. This CARBO-IRON (20 wt-% zero-valent iron) has proved its suitability as a dehalogenation reagent applicable for both plume and source treatment.

Guided Assembly of Gold Colloidal Nanoparticles on Silicon Substrates Prepatterned by Charged Particle Beams

Colloidal gold nanoparticles represent technological building blocks which are easy to fabricate while keeping full control of their shape and dimensions. Here, we report on a simple two-step maskless process to assemble gold nanoparticles from a water colloidal solution at specific sites of a silicon surface. First, the silicon substrate covered by native oxide is exposed to a charged particle beam (ions or electrons) and then immersed in a HF-modified solution of colloidal nanoparticles. The irradiation of the native oxide layer by a low-fluence charged particle beam causes changes in the type of surface-terminating groups, while the large fluences induce even more profound modification of surface composition. Hence, by a proper selection of the initial substrate termination, solution pH, and beam fluence, either positive or negative deposition of the colloidal nanoparticles can be achieved.

Surface-enhanced Raman scattering of SnO2bulk material and colloidal solutions

Surface-enhanced Raman scattering (SERS) effects on tin dioxide in the form of bulk material, nanostructured thin films, and colloidal solutions were investigated. Raman spectra are characterized by the three Raman scattering peaks at 478, 633, and 776 cm${}^{\ensuremath{-}1}$, assigned to the ${E}_{g}$, ${A}_{1g}$, and ${B}_{2g}$ modes, typical of rutile SnO${}_{2}$. In the presence of the silver nanoparticles, in addition to the enhancement intensity of some of the fundamental tin dioxide rutile Raman features, the appearance of a new Raman scattering peak at about 600 cm${}^{\ensuremath{-}1}$ is observed. These spectral features are observed, in the presence of silver nanoparticles, also in other SnO${}_{2}$-based systems such as pulsed laser deposited thin films, with different stoichiometry, and in water colloidal solutions. The observed SERS effects are explained in terms of electric field gradient mechanism that are generated near a metal surface. In particular, the appearance of a peak near 600 cm${}^{\ensuremath{-}1}$ is attributed to the Raman activation of the infrared ${E}_{u}$ transverse optical mode.

A structural study of biocompatible magnetic nanofluid with synchrotron radiation-based X-ray scattering techniques

In this paper, water colloidal solutions of nanoparticles of magnetite (magnetic nanofluids, (MNFs)) are investigated by synchrotron X-ray diffraction (XRD) and small-angle scattering (SAXS). To prevent aggregation, nanoparticles are coated with polyacrylic acid (PAA) in a single solution and citric (CA) in the other solutions. In both cases, the maxima of the particle size distribution from SAXS (9–10 nm) correspond to the sizes of the magnetite crystallites that were estimated from the broadening of the diffraction lines. In addition, the SAXS data indicate the presence of a significant proportion of aggregates (up to 60 nm in diameter) in both colloidal solutions, although fundamental differences in the structures of aggregates between the MNFs stabilized by PAA and CA were not observed. In this study determination of the structural characteristics of MNFs were carried out in order to obtain stable dispersive non-aggregating nanoparticles of magnetite for use as contrast agents in magnetic resonance tomography, drug carriers, and other biomedical applications.

Swelling of Protective Gloves in Commercial TiO2 Nanoparticles Colloidal Solutions

Titanium dioxide (TiO2) nanoparticles enter in the composition of numerous manufactured products such as sunscreens or paints for example and their use seems today inescapable. Some of them are delivered in colloidal solutions to reduce aerolization risks. However, elastomers used in the manufacture of protective gloves may be sensitive to the action of solvents employed as liquid carriers in these commercial nanoparticles solutions. Effects may involve the swelling of the polymer by the solvent. If the solvent emerges on the inner side of the protective glove, it may carry nanoparticles with it, thus facilitating their penetration through gloves. This work aims at studying the swelling of four elastomers used in protective gloves when immersed in TiO2 colloidal solutions as well as in technical and ultra-pure solvents corresponding to the liquid carriers used in the nanoparticles solutions. The study involves latex, neoprene, nitrile and butyl rubber gloves and three commercial TiO2 colloidal solutions in water, 1,2-propanediol and 1,2-ethanediol. The swelling behaviour was assessed by mass gain and length change measurements. It was observed that the studied solutions have a significant swelling effect on nitrile rubber, latex and neoprene. On the other hand, no effect was measured with butyl rubber. As revealed by the non-negligible swelling recorded even for short immersion times, a possibility exists for a liquid carrier-mediated penetration of TiO2 nanoparticles through these protective gloves. These results are in agreement with preliminary measurements showing by chemical analysis of sampling solutions a possible penetration of TiO2 nanoparticles through gloves when in colloidal solutions. This demonstrates that great care must be taken when selecting protective gloves for handling nanoparticles in solutions.

Deagglomeration and surface modification of thermally annealed nanoscale diamond

Thermally annealed nanodiamond has been functionalized by C–C coupling of the partially graphitized diamond surface using aryl diazonium salts. Depending on the terminal functional groups, the modified bucky diamond nanoparticles show good solubility (up to 0.63 mg mL −1) in different solvents. The agglomerate size of the originally strongly bound detonation diamond (>0.5 μm) is substantially reduced to ∼20–50 nm by this chemical procedure and without using mechanical techniques such as strong ultrasound or milling. Arylation with functionalized aryl diazonium salts carrying COOH, SO 3H, NO 2 or bromoethyl groups opens the way for further covalent grafting of organic structures. Arylation with Ar–COOH or Ar–SO 3H leads to the formation of stable colloidal solutions in water and physiological media (i.e. PBS buffer), an important prerequisite for biomedical applications.

Electrogenerated Chemiluminescence of Aromatic Hydrocarbon Nanoparticles in an Aqueous Solution

We report the preparation, characterization, and electrogenerated chemiluminescence (ECL) of rubrene nanoparticles (NPs) and 9,10-diphenylanthracene (DPA) nanorods. The organic NPs were prepared in an aqueous phase using a simple reprecipitation method, i.e., injecting a solution of the hydrocarbon in an organic solvent into water. The resulting NPs can be collected and redispersed to form stable colloidal solutions in water. Rubrene forms spherical nanoparticles (NPs) (diameter ∼50 nm), while DPA initially forms nanorods with an average size of ∼500 nm in length and ∼50 nm in diameter. DPA nanorods grew gradually with time into wires with diameters of ∼1 μm and lengths of ∼10 μm. ECL emission from these NPs was observed upon electrochemical oxidation in aqueous solutions containing different co-reactants, such as tri-n-propylamine for rubrene and an oxalate ion for DPA NPs. The ECL intensity from rubrene NPs was significantly higher than that from DPA NPs because of the smaller size, and thus there is a higher diffusion coefficient for rubrene as compared to that of DPA NPs.

Ultrathin film assembly of sulfobetaine-stabilized palladium nanoparticles investigated by photoemission spectroscopy

Thin films of sulfobetaine-stabilized palladium nanoparticles on a gold surface were prepared by evaporation of their colloidal water solution and investigated by ultraviolet photoemission spectroscopy. The photoemission from the thin films was found to be dominated entirely by the surfactant molecules. No photoemission from the gold substrate was observed; these facts strongly suggest the formation of uniform (hole-free) thin films of the surfactant-stabilized nanoparticles. Additional investigation of structural degradation using neon-ion sputtering also supports the film condition.

Fiber and film formation by self-assembly of colloidal silicalite-1 and copper coated silicalite-1 nanocrystals

Silicalite-1 nanocrystals with sizes of 20 and 74 nm were synthesized and stored as colloidal solutions in water or ethanol. The self-assembly of the colloidal silicalite-1 nanocrystals into thin films and transparent, rectangular fibers was monitored. Monodispersed and binary colloidal silicalite-1 nanocrystals both formed rectangular fibers through close packing of the nanocrystals. The formation of fibers or thin films was controlled by varying the concentration of the colloidal solutions. At higher concentration, fibers were formed, while very diluted colloidal solutions resulted in thin films. Calcination of the fibers or thin films did not damage the zeolite structures. Two methods were developed to coat copper metal onto the silicalite-1 nanocrystals. Silicalite-1 fibers and films coated with copper were conductive materials.

Physicochemical characterization of protamine-phosphorothioate nanoparticles

Protamine-oligonucleotide nanoparticles represent effective colloidal drug carriers for antisense phosphorothioate oligonucleotides (PTO). This study describes improvements in particle preparation and the physicochemical properties of the complexes prepared. The influence of component concentrations, length of the PTO chain and the PTO/protamine weight ratio on particle formation and size, shape and surface charge of the particles were studied in detail. Nanoparticles with diameters of 90–200 nm were obtained, using protamine free base (PFB) and phosphorothioate in water. The chemical composition of the nanoparticles was analysed. More than 90% of the PTO could be assembled in the particle matrix using a ≥1 : 2 ratio (w/w) of PTO and PFB. About 53–68% of the PFB was incorporated in the particle matrix. The complexes had a zetapotential of −19 up to +32 mV, depending on the PTO/PFB ratio. The kinetics of the assembly of this binary system were observed by dynamic light scattering (DLS) measurements and by sedimentation velocity analysis in the analytical ultracentrifuge (AUC). In addition, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were applied to verify the results of DLS and the ultracentrifuge measurements. According to sedimentation velocity analysis, the particles were only moderately stable in water and unstable in salt solutions. However, the colloidal solution in water could be stabilized by polyethylenglycol 20 000 (PEG), which also led to an increase of stability in cell medium.

Spherical and Planar Gold(0) Nanoparticles with a Rigid Gold(I)−Anion or a Fluid Gold(0)−Acetone Surface

We propose here a new model for gold nanoparticles, which are thought to be solubilized by either a Au(I)−citrate or Au(I)−sulfide layer. In the case of pure Au(0) particles, stabilization of the colloidal solutions occurs by inverse micelles or by tight adsorption of solvent covers, in particular acetone. The main evidence for this model is as follows: Standard 20 nm citrate gold particles precipitate from the red colloidal solution in water in the form of a black metal powder after addition of sodium borohydride or as blue coagulate after acidification with HCl. Both processes are irreversible. If the same particles are carrying a lipoate coating, they dissolve in water at pH 11, coagulate at pH 3, and redissolve quantitatively at pH 11. This cycle has been repeated several times without any change of the 20 nm particles. No irreversible color change of the colloidal solution or fusion of the particles takes place upon acid−base treatment. Sodium borohydride, on the other hand, precipitates the lipoate...

Intelligent colloidal hybrids via reversible pH-induced complexation of polyelectrolyte and silica nanoparticles.

We present novel intelligent colloidal polymer/silica nanocomposites, in which the complexation of cationic silica nanoparticles and a weak anionic polyelectrolyte can be manipulated simply by pH change through a hydrogen-bonding interaction and ionic complexation caused by hydrogen-transfer interactions between the constituents. Special silica particles which have nanometer size (diameter approximately 3.0 nm) and two independent proton-accepting sites were developed in this study. Both the silica and poly(acrylic acid) form transparent colloidal solutions in water, while a white turbid dispersion was obtained just after mixing the two solutions due to the complexation. The pH-induced association-dissociation behavior was confirmed by the turbidity and potentiometric titration measurements. The assembled structures of the hybrids were visualized by scanning force microscopy.