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PubMed2003

Use of optical tweezers for colloid science.

A space-borne optical tweezer apparatus for use with colloidal crystallization experiments has been characterized. The trapping force has been measured as a function of index mismatch between colloidal microspheres and the surrounding fluid and as a function of particle size. This work also presents a method to determine the refractive index of a colloidal microsphere, which is then used to calculate the applied trapping force for the case of an arbitrary background fluid. This is useful for work with dense colloidal suspensions when the usual (e.g., Stokes flow) trap force measurement methods do not apply, as well as microrheological studies of complex soft matter.

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PubMed2003

Structure and rheological behavior of highly charged colloidal particles in a cylindrical pore I. Effect of pore size.

In this work we performed nonequilibrium Brownian dynamics (NEBD) computer simulations of highly charged colloidal particles in diluted suspension under a parabolic flow in cylindrical pores. The influence of charged and neutral cylindrical pores on the structure and rheology of suspensions is analyzed. A shear-induced disorder-order-disorder-like transition was monitored for low shear rates and small pore diameters. We calculate the concentration profiles, axial distribution functions, and axial-angular pair correlation functions to determine the structural properties at steady state for a constant shear flow for different pore sizes and flow strengths. Similar behavior has been observed in a planar narrow channel in the case of charged interacting colloidal particles (M.A. Valdez, O. Manero, J. Colloid Interface Sci. 190 (1997) 81). The mobility of the particles in the radial direction decreases rapidly with the flow and becomes practically frozen. The flow exhibits non-Newtonian shear thinning behavior due to interparticle interactions and particle-wall interaction; the apparent viscosity is lower as the pore diameter decreases, giving rise to an apparent slip in the colloidal suspension. The calculated slip velocity was higher than that obtained in a rectangular slit under shear flow.

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PubMed2002

Familial colloid cyst of the third ventricle: neuroendocrinological follow-up and review of the literature.

Colloid cysts of the third ventricle are rare, benign cysts of endodermal origin. Between 1989 and 1999, eight patients with this lesion (five females, three males), with a mean age of 40.5 years (range 20-54), were identified out of 1354 operated for tumours of the central nervous system. Among the eight, two were familial. They were half sisters 38 and 28 years-old, who were diagnosed to have colloid cysts of the third ventricle on CT scanning. Transcortical excision yielded 10 and 15 mm sized colloid cysts, respectively. Moreover, both sisters developed a multinodular goiter associated with these congenital tumours. The second sibling developed hyperprolactinemia associated with macroprolactinemia. Pregnancy was only possible after bromocriptine treatment. These cases provide further evidences that colloid cysts probably have an autosomic recessive pattern of inheritance with variable penetrance.

Adult↗
PubMed1999

Improved cardiac preservation by the addition of nitroglycerine to colloid-free University of Wisconsin solution (MUW).

BACKGROUND: This study examines whether the addition of nitroglycerine, a known coronary vasodilator and nitric oxide donor, to colloid-free University of Wisconsin solution will improve and extend cardiac preservation. METHODS: Rat hearts were flushed and stored in colloid-free University of Wisconsin solution with or without the addition of nitroglycerine for 12, 16 or 20 hours at 0 degrees C before heterotopic transplantation with an indwelling externalized intraventricular balloon-tipped catheter. One and 7 days after transplantation of the heart the catheter was connected to a pressure transducer and quantitative functional studies were performed. RESULTS: After 12 hours preservation with nitroglycerine in colloid-free University of Wisconsin solution 6/6 grafts continued to beat for 7 days compared to 3/6 without nitroglycerine. After 16 hours preservation the addition of nitroglycerine 5/7 hearts continued to beat for 7 days compared to 0/6 without nitroglycerine (p < .05). Only 1/6 hearts beat for 7 days after 20 hours preservation with nitroglycerine. On Days 1 and 7, the left ventricular developed pressure (LVDP), contractility (max dP/dt) and rate of relaxation (peak -dP/dt) of 12 hour preserved hearts was better (p < .05) when nitroglycerine was present. The function of hearts preserved with the addition of nitroglycerine was similar after 12 and 16 hours preservation. CONCLUSION: Nitroglycerine is a valuable additive to colloid-free University of Wisconsin solution, extending effective preservation of the rat heart to 16 hours and significantly improving left ventricular function after 12 and 16 hours preservation. The addition of nitroglycerine, however, did not extend preservation to 20 hours.

Adenosine↗
PubMed1998

Correlative Instrumental Neutron Activation Analysis, Light Microscopy, Transmission Electron Microscopy, and X-ray Microanalysis for Qualitative and Quantitative Detection of Colloidal Gold Spheres in Biological Specimens.

: Colloidal gold, conjugated to ligands or antibodies, is routinely used as a label for the detection of cell structures by light (LM) and electron microscopy (EM). To date, several methods to count the number of colloidal gold labels have been employed with limited success. Instrumental neutron activation analysis (INAA), a physical method for the analysis of the elemental composition of materials, can be used to provide a quantitative index of gold accumulation in bulk specimens. Given that gold is not naturally found in biological specimens in any substantial amount and that colloidal gold and ligand conjugates can be prepared to yield uniform bead sizes, the amount of label can be calculated in bulk biological samples by INAA. Here we describe the use of INAA, LM, transmission EM, and X-ray microanalysis (EDX) in a model to determine both distribution (localization) and amount of colloidal gold at the organ, tissue, cellular, and ultrastructural levels in whole animal systems following administration. In addition, the sensitivity for gold in biological specimens by INAA is compared with that of inductively coupled plasma-mass spectrometry (ICP-MS). The correlative use of INAA, LM, TEM, and EDX can be useful, for example, in the quantitative and qualitative tracking of various labeled molecular species following administration in vivo.

Journal Article↗
PubMed2001

Characterization of silane-modified immobilized gold colloids as a substrate for surface-enhanced Raman spectroscopy.

Immobilized gold colloid particles coated with a C-18 alkylsilane layer have been characterized as a substrate for surface-enhanced Raman scattering (SERS) studies of adsorption onto hydrophobic surfaces. Atomic force microscopy images, optical extinction spectra, and SERS measurements are reported as a function of accumulation of gold colloid on glass. As the metal particles become increasingly aggregated on the surface, the SERS enhancement increases until the plasmon resonance shifts to wavelengths longer than the excitation laser. The gold colloid substrates are stable and exhibit reproducible SERS enhancement. When octadecyltrimethoxysilane is self-assembled over the gold, the metal surface is protected from exposure to solution-phase species, as evidenced by the inhibition of chemisorption of a disulfide reagent to the overcoated gold surface. The results show that interactions with gold can be blocked by a silane layer so as not to significantly influence physisorption of molecules at the C-18/solution interface. The SERS enhancement from these C-18-overcoated gold substrates is reproducible for different films prepared from the same colloidal suspension; the substrates are also stable with time and upon exposure to laser irradiation.

Journal Article↗
PubMed2005

Surface-enhanced Raman spectroscopy substrate composed of chemically modified gold colloid particles immobilized on magnetic microparticles.

In this paper, immobilization of gold colloidal particles onto amine-modified magnetic microparticles is demonstrated. Once immobilized, the gold was then reacted with pentachlorothiophenol (PCTP) to form a self-assembled monolayer. The PCTP-gold colloid on magnetic microparticles was then used to extract naphthalene from aqueous samples. A magnet was used to concentrate the microparticles onto the side of the sample vial, allowing detection of naphthalene by surface-enhanced Raman spectroscopy. Using the PCTP-gold colloid on magnetic microparticles the limit of detection for naphthalene achieved was 0.3 microg mL(-1). Multiple extractions can be done with the PCTP-gold colloid on magnetic microparticles to further lower the detection limit.

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PubMed2004

Colloid-imprinted carbons as stationary phases for reversed-phase liquid chromatography.

A novel colloid-imprinting method is employed for the preparation of carbonaceous stationary phases for reversed-phase liquid chromatography (RPLC). This colloid-imprinting method combined with oxidative stabilization treatment affords carbons with a porous shell/nonporous core structure. The particle morphology, pore size, pore shape, and Brunauer-Emmett-Teller surface area of these carbons can be finely tuned by selecting proper experimental conditions. Although their surface area and pore volume decrease noticeably after graphitization, their primary pore structure is maintained. In addition, the graphitization process eliminates the high-energy sites and substantially reduces structural heterogeneity, making colloid-imprinted carbons attractive stationary phases for reversed-phase liquid chromatography. The colloid-imprinted graphitic carbons with surface mesoporosity appeared to be attractive for chromatographic separations of alkylbenzenes under reversed-phase conditions.

Journal Article↗
PubMed2000

On-column surface-enhanced Raman spectroscopy detection in capillary electrophoresis using running buffers containing silver colloidal solutions

Direct on-column surface-enhanced Raman spectroscopy (SERS) detection is demonstrated in capillary electrophoresis (CE). Distinctive SERS spectra of two test compounds, riboflavin and Rhodamine 6G, are obtained in 100 microm i.d. fused-silica capillaries under CE conditions using running buffers that contain silver colloidal solutions. Detection is performed using an unmodified commercial Raman spectrometer in a confocal microscope mode of operation. The effects of laser power, wavelength, spectra acquisition time, silver colloidal concentration, and applied voltage (i.e., flow rate) on the quality of SERS spectra are evaluated. Using laser powers of 17 mW (at the sample) at 515 nm and employing 1 s spectral acquisition times, spectra with bands exhibiting signal-to-noise ratios greater than 10 could be obtained for 1.0 x 10(-6) M riboflavin and very low nanomolar concentrations of Rhodamine 6G. This was accomplished without optimization of silver colloidal solution compositions and by using a low-throughput spectrometer. Incorporation of the colloidal solutions into running buffers is shown to have little effect on the separation of the test compounds as monitored using a laser-induced fluorescence instrumental scheme. However, SERS spectra degrade if the capillary is not rinsed between experiments. Riboflavin and Rhodamine 6G spectra are obtained on-the-fly for actual CE separations. In the case of the latter solute, the injected quantity was approximately 90 amol.

Journal Article↗
PubMed2002

XAFS investigation of the structure of aqueous thorium(IV) species, colloids, and solid thorium(IV) oxide/hydroxide.

X-ray absorption fine structure (XAFS) spectroscopy at the Th L3 edge is applied for the characterization of crystalline, anhydrous ThO(2)(cr), microcrystalline ThO(2).xH(2)O(s), amorphous ThO(n)(OH)(4-2n).xH(2)O(am), aqueous Th(IV) solutions, and colloidal suspensions up to p(c)H 3.7. The microcrystalline, possibly hydrated thorium dioxide, is formed at p(c)H 1.5-2.5 by precipitation from suspensions of 16-23 nm thorium dioxide colloids. The solubility data determined for this solid is several orders of magnitude lower than the values for amorphous Th(IV) hydroxide or hydrous oxide. The EXAFS spectrum of the isolated microcrystalline particles shows that their structure is different from that of anhydrous crystalline ThO(2)(cr) and amorphous ThO(n)(OH)(4-2n).xH(2)O(am) precipitated at higher pH and dried at room temperature. The solubility measured for the amorphous Th(IV) precipitate is comparable to that previously reported for a solid prepared in a similar manner. In other solubility studies with amorphous Th(IV) hydroxide or hydrous oxide, considerably higher thorium concentrations are measured at p(c)H 3.5-5. The aqueous speciation is made by EXAFS for solutions prepared by careful coulometric titration under comparable conditions (p(c)H and thorium concentration). The spectra of these solutions demonstrate the presence of a large amount of Th(IV) polynuclear species or colloids of small size, having a highly asymmetric Th-O coordination. The EXAFS spectrum of these colloids is similar to that of the amorphous solid.

Journal Article↗
PubMed2002

Dynamic distribution of growth rates within the ensembles of colloidal II-VI and III-V semiconductor nanocrystals as a factor governing their photoluminescence efficiency.

The distribution of properties within ensembles of colloidally grown II-VI and III-V semiconductor nanocrystals was studied. A drastic difference in the photoluminescence efficiencies of size-selected fractions was observed for both organometallically prepared CdSe and InAs colloids and for CdTe nanocrystals synthesized in aqueous medium, indicating a general character of the phenomenon observed. The difference in the photoluminescence efficiencies is attributed to different averaged surface disorder of the nanocrystals originating from the Ostwald ripening growth mechanism when larger particles in the ensemble grow at the expense of dissolving smaller particles. At any stage of growth, only a fraction of particles within the ensemble of growing colloidal nanocrystals has the most perfect surface and, thus, shows the most efficient photoluminescence. This is explained by a theoretical model describing the evolution of an ensemble of nanocrystals in a colloidal solution. In an ensemble of growing nanocrystals, the fraction of particles with the highest photoluminescence corresponds to the particle size having nearly zero average growth rate. The small average growth rate leads to the lowest possible degree of surface disorder at any given reaction conditions.

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PubMed2003

Sulfonic Acid-functionalized gold nanoparticles: a colloid-bound catalyst for soft lithographic application on self-assembled monolayers.

In this report, we present a new lithographic approach to prepare patterned surfaces. Self-assembled monolayers (SAMs) of the acid-labile trimethylsilyl ether (TMS-OC(11)H(22)S)(2) (TMS adsorbate) was formed on gold. 5-Mercapto-2-benzimidazole sulfonic acid sodium salt (MBS-Na(+)) was used as a ligand for gold nanoparticles. These monolayer-protected gold colloids (MPCs) were transformed into the catalytically active H(+)-form by ion exchange. This colloid-bound catalyst hydrolyzed the TMS adsorbate (TMS-OC(11)H(22)S)(2) both in solution and when self-assembled on gold surfaces. Microcontact printing of the active colloid-bound catalyst on the preformed TMS SAM led to the deposition of the colloid onto the SAMs. After the catalyst nanoparticles were rinsed off, a patterned surface was created as shown by AFM.

Journal Article↗
PubMed2003

Asymmetric dimers can be formed by dewetting half-shells of gold deposited on the surfaces of spherical oxide colloids.

Asymmetric dimers consisting of gold microcrystals and spherical silica colloids have been fabricated by depositing thin films of gold onto the spherical colloids to form half-shells, followed by annealing at elevated temperatures. The capability and feasibility of this procedure have been demonstrated with silica and titania beads of 0.2-2 mum in diameter and gamma-Fe2O3/polystyrene@SiO2 core-shell particles 0.5 mum in size. The dimensions of gold microcrystals could be conveniently varied in the range of 100-650 nm by controlling the thickness of gold films and/or the diameter of the spherical colloids. This method provides another route to asymmetric dimers made of colloidal particles that could be different in size, chemical composition, surface functionality, density or sign of surface charge, bulk property, or a combination of these properties.

Journal Article↗
PubMed2005

Controlled electrophoretic patterning of polyaniline from a colloidal suspension.

We present a method for controlled deposition of polyaniline from colloidal suspensions. Stable suspensions of polyaniline colloids (approximately 115 nm in diameter) were formed by dispersing polyaniline/formic acid solution into acetonitrile. It was demonstrated that the positively charged polyaniline colloids can be electrophoretically deposited onto various substrate materials such as platinum and ITO, forming continuous ultrathin films. We examined the film morphology, as well as the effects of process parameters, such as deposition time, colloid concentration, and applied voltage, on the deposition efficiency. Furthermore, the efficacy of the technique was illustrated by electrophoretically patterning polyaniline thin films onto selected individual micrometer-scale sensing elements within a microfabricated sensor array, and by further demonstrating its sensitivity to gaseous analytes including water and methanol.

Journal Article↗
PubMed2004

Microcontact printing of colloidal crystals.

Patterned two-dimensional (2D) colloidal crystals have been transferred by a modified mucp technique that was based on the use of polymer film as "glue" to provide an efficient interaction between the microsphere "ink" and substrate. The versatility of this method has been demonstrated by the patterning of colloidal crystal on a nonplanar substrate and heterogeneously structured colloidal crystal film. The table of contents graphic shows an SEM image of the ordered parallel lines of 2D colloidal crystals on a polymer-coated glass tube with a 3.7 mm radius of curvature.

Journal Article↗
PubMed2004

Colloidal crystallization and banding in a cylindrical geometry.

Colloidal crystallization takes advantage of the strong interfacial forces and tunable interactions that organize particles into regular structures at small scales. Thus, colloidal crystallization and patterning provide a powerful and simple method to functionalize planar surfaces with applications to optical, catalytic, sensing, and cleansing materials. Nevertheless, the ability to pattern topologically more complex surfaces such as curved, confined, or soft substrates can open new avenues for novel, "intelligent", and responsive materials. We present one step in this direction by characterizing colloidal crystallization inside circular capillaries: a nearly periodic banding is observed, and the colloidal packing is dictated by confinement produced by the wedge-like region formed by a capillary confined meniscus. The packing consists of a succession of hexagonally close-packed regions, which are separated by narrow regions of "buckled phase crystals".

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PubMed2006

Polymer-coated ferromagnetic colloids from well-defined macromolecular surfactants and assembly into nanoparticle chains.

A novel synthetic route to polymer-coated ferromagnetic colloids of metallic cobalt has been developed. Well-defined end-functional polystyrenes were synthesized using controlled radical polymerization and used as surfactants in the thermolysis of dicobaltoctacarbonyl to afford uniform ferromagnetic nanoparticles. The presence of the polymer shell enabled prolonged colloidal stability of dispersions in a wide range of organic solvents and formed glassy encapsulating coatings around ferromagnetic cores in the solid state. These polymer-coated colloids assembled into robust, micron-sized nanoparticle chains when cast onto supporting surfaces due to dipolar associations of magnetic cores. Hierarchical assemblies were also prepared by blending polystyrene-coated cobalt colloids with larger silica beads.

Journal Article↗
PubMed2005

Synthesis and real-time magnetic manipulation of a biaxial superparamagnetic colloid.

Superparamagnetic colloidal plates were synthesized from tetrabutylammonium stabilized Ca(2)Nb(3)O(10) nanosheets and oleic acid-stabilized Fe(3)O(4) nanoparticles. Modification with 3-aminopropyltrimethoxysilane produces amine-terminated Ca(2)Nb(3)O(10) with an amine concentration of 0.43 +/- 0.06 groups per Ca(2)Nb(3)O(10) unit as follows from spectroscopic quantification with trinitrobenzenesulfonic acid as a dye. Treatment of the modified sheets in THF/ethanol with 5.3 nm oleic acid-stabilized magnetite nanoparticles yields pseudo-2D assemblies that consist of 2 nm thick nanosheets decorated on both sides with a dense collection (9.3 +/- 0.5 x 10(3) particles per square micrometer per side) of magnetite particles. In noncoordinating or weakly coordinating solvents, these composite particles further aggregate into stacked aggregates with a mean edge length of 1.6 +/- 0.7 microm and a thickness of 79 +/- 30 nm. The colloidal plates were characterized by elemental analysis, X-ray powder diffraction, and infrared and UV/vis spectroscopy. SQUID measurements show that films of the aligned particles are superparamagnetic at room temperature. The magnetic hysteresis that is observed at 5 K reveals that the plates have a magnetic anisotropy with the easy axis in the plane of the plates and the hard axis perpendicular to it. Calculations show that the magnetic anisotropy is a direct consequence of the two-dimensional distribution of the magnetic nanoparticles on the sheets. Optical microscopy reveals that when suspended in ethanol or THF, the colloidal plates can be rotated in real time with a variable external magnetic field (200 Oe). Magnetic alignment of the particles in suspensions also produces asymmetric light scattering patterns and magnetic birefringence. These effects and the observed magneto-orientational properties make the biaxial colloids interesting as components in displays and as magnetic actuators.

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