Small Colloids Research Articles

Near Infrared Tunable Gold Nanoparticles for Low Power Laser Ablation of Esophageal Adenocarcinoma

ABSTRACTGold nanoparticles (GNPs) with precisely controlled near infrared (NIR) absorption were synthesized by one-step reaction of chloroauric acid and sodium thiosulfate. The NIR absorption wavelengths and average particle size increase with increasing molar ratio of HAuCl4/Na2S2O3. The as-synthesized GNPs consist of different shape and size, including small spherical gold colloids and larger non-spherical gold crystals. The GNPs with good chemical and optical stability only form in a suitable range of the HAuCl4/Na2S2O3 molar ratio. High molar ratio of HAuCl4/Na2S2O3 reduces GNPs stability due to Ostwald ripening. Chitosan coating improves particle stability and allows these GNPs effective ablation for esophageal adenocarcinoma under low power NIR laser radiation.

Synthesis of rod-like silica–gold core-shell structures

Synthesis of rod-like silica–gold core-shell structures is reported by using silica rods having length of ∼1 μm and diameter of ∼200 nm. Before deposition of gold nanoparticles the aforementioned silica rods were modified by using 3-aminopropyltrimethoxysilane (APTMS) in order to attach aminopropyl groups and consequently, to facilitate deposition of Au. There methods were used to deposit Au nanoparticles. The first method of deposition was performed by using nanosized Au nanoparticles obtained by reduction of tetrachloroauric acid with borohydride. The second route was performed by direct reduction of tetrachloroauric acid with formaldehyde, which led to the formation of Au nanoparticles of about 50 nm. In the third route Au nanoparticles were obtained by reduction tetrachloroauric acid with borohydride but their deposition was carried out on the silica rods pre-decorated with small Au colloids. Each of these methods led to the formation of Au less or more uniform nanoshells on siliceous rods.

Arsenic removal by ferric-chloride coagulation – effect of phosphate, bicarbonate and silicate

Jar tests with synthetic water were carried out in order to investigate the effect of phosphate, bicarbonate and silicate on arsenic removal efficiency by in-situ formed ferric hydroxide. Above 12 mg C/L inorganic carbon concentration, the adverse effect of bicarbonate was definite, and resulted in higher remaining arsenic concentration. At all pH values (7.5-7.8) and coagulant dosages (0.84-3.00 mg/L Fe) tested, the negative effect of phosphate on arsenic removal was also evident. In the presence of silicate small ferric-hydroxide colloids were formed, which were able to go through the 0.45 microm pore-size membrane. Compared to silicate-free systems, 2.5-3.5 times higher coagulant dose was needed to achieve the target arsenic concentration in the presence of 14-23 mg/L Si. At higher pH values the adverse effect of silicate was even more significant. All data were merged and multiple linear regression analysis was carried out in order to build up a robust model to predict the residual arsenic concentration if the raw water contains 50-60 microg/L initial arsenic concentration. The estimation was based on the following variables: PO4-P concentration, final pH, Si concentration, Fe(III) dose. The most important influencing factors proved to be the silicate concentration and applied coagulant dosage.

Purely Endoscopic Removal of Intraventricular Brain Tumors: A Consensus Opinion and Update

The main purpose of this project is to define the major indications, preferences, techniques, limitations, and complications associated with intraventricular tumor removal using purely endoscopic techniques. Published papers on neuroendoscopy were reviewed, and a questionnaire about purely endoscopic surgery for intraventricular brain tumors was designed. The questionnaire included details regarding neuroendoscopic techniques, surgeons' endoscopic experience, and clinical vignettes. 20 experienced neuroendoscopists from the 10 represented countries were surveyed. 15 physicians (75%) responded to the survey, having an estimated 264 cumulative years of endoscopic experience. There was general agreement regarding: the instrumentation used, endoscope features, irrigation, technique of colloid cyst and solid intraventricular tumor removal, complications, future technologies, and the treatment of sample clinical vignettes. There was appreciable variability in endoscope control preferences. Endoscopic intraventricular surgery is a feasible minimally invasive alternative to open transcranial surgery for specific ventricular tumors. With the currently available instrumentation, the technique can be applied to small avascular solid intraventriclular tumors and colloid cysts of the third ventricle. The majority of the complications are based on hemostasis potential. The development of compatible instrumentation with an enhanced ability for solid tumor removal and more adequate hemostasis appear to be the principle limitations in furthering the technique of endoscopic removal of intraventricular brain tumors.

ChemInform Abstract: Design and Elaboration of Colloidal Molecules: An Overview

AbstractReview: 146 refs.

Wafer‐Scale Fabrication of Ordered Binary Colloidal Monolayers with Adjustable Stoichiometries

AbstractColloidal monolayers with high order and increased complexity beyond plain hexagonal packing geometries are useful for 2D templating of surface nanostructures and lithographic applications. Here, binary colloidal monolayers featuring a close‐packed monolayer of large spheres (L) with a superlattice of small particles (S) are prepared in a single step using a Langmuir trough. Adjustment of the stoichiometry of the two particle types at the air–water interface leads to a high degree of control over the occupation of the interstitial sites in the close‐packed layer of large spheres by the small colloids. Thus, large areas of binary 2D crystals with LS2, LS6, and LS9 structures are fabricated in a controlled way. The process allows the formation of binary crystals over a wide range of particle size ratios from 0.19 to 0.40. The pH value of the subphase can be used to enhance the crystallization process by changing the contact angle of the particles at the interface. An interfacial polymerization of butyl cyanoacrylate is used to directly image the contact angle of the colloids at the interface. Transfer to solid substrates is achieved by a surface lowering technique. A variety of substrates with arbitrary topographies can thus be decorated with colloidal monolayers. Applied to a lithographic process, such monolayer architectures allow the generation of complex patterns, not accessible with conventional close‐packed monolayers.

Mechanisms controlling lateral and vertical porewater migration of depleted uranium (DU) at two UK weapons testing sites

Uranium associations with colloidal and truly dissolved soil porewater components from two Ministry of Defence Firing Ranges in the UK were investigated. Porewater samples from 2-cm depth intervals for three soil cores from each of the Dundrennan and Eskmeals ranges were fractionated using centrifugal ultrafiltration (UF) and gel electrophoresis (GE). Soil porewaters from a transect running downslope from the Dundrennan firing area towards a stream (Dunrod Burn) were examined similarly. Uranium concentrations and isotopic composition were determined using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and Multi-Collector-Inductively Coupled Plasma-Mass Spectrometry (MC-ICP-MS), respectively. The soils at Dundrennan were Fe- and Al-rich clay–loam soils whilst at Eskmeals, they were Fe- and Al-poor sandy soils; both, however, had similar organic matter contents due to the presence of a near-surface peaty layer at Eskmeals. These compositional features influenced the porewater composition and indeed the associations of U (and DU). In general, at Dundrennan, U was split between large (100 kDa–0.2 μm) and small (3–30 kDa) organic colloids whilst at Eskmeals, U was mainly in the small colloidal and truly dissolved fractions. Especially below 10 cm depth, association with large Fe/Al/organic colloids was considered to be a precursor to the removal of U from the Dundrennan porewaters to the solid phase. In contrast, the association of U with small organic colloids was largely responsible for inhibiting attenuation in the Eskmeals soils. Lateral migration of U (and DU) through near-surface Dundrennan soils will involve both large and small colloids but, at depth, transport of the smaller amounts of U remaining in the porewaters may involve large colloids only. For one of the Dundrennan cores the importance of redox-related processes for the re-mobilisation of DU was also indicated as Mn IV reduction resulted in the release of both Mn II and U VI into the truly dissolved phase.

The removal of colloidal lead during estuarine mixing: seasonal variations and importance of iron oxides and humic substances

In the present study, seven colloidal fractions of lead (Pb) were analysed along the mixing zone of the Penzé estuary over the Year 2009, with the aim to provide some insight into the mechanism that removes the metal from the <0.45-µm fraction. According to our results, Pb was generally found as large colloids (>300 kDa) and was removed in the salinity range 0–10 from all of the size fractions where it was significantly found. Because the colloidal fractionation of Pb was strongly linked to that of iron (Fe) and humic substances (HS), the removal of Pb in the mixing area must occur under flocculation of organomineral complexes. A key period corresponding to the first strong autumnal precipitations was also revealed in the present work. At this time of the year, the mobilisation of Pb (and Fe) from catchment soils is enhanced by the mobilisation of HS and the metal is associated with smaller colloids (30–300 kDa).

Design and elaboration of colloidal molecules: an overview

The concept of colloidal molecules was first evoked by van Blaaderen in 2003 for describing small non-spherical colloids made of the aggregation of a small number of particles. He predicted original properties to the complex assemblies of such colloids, in particular in optics. This critical review deals with the different strategies reported for creating robust clusters of spherical particles which could mimic the space-filling models of simple conventional molecules. These routes concern either the controlled clustering of preformed colloids directed by coalescence, physical routes, chemical routes, or 2-D/3-D geometrical confinement, or strategies starting from a single colloid which is decorated by satellite colloids by taking advantage of controlled phase separation or nucleation and growth phenomena. These routes are compared from the viewpoint of the accessible shapes, their tunability and scalability (146 references).

Nucleation.

Crystallization starts with nucleation and control of nucleation is crucial for the control of the number, size, perfection, polymorphism and other characteristics of crystalline materials. This is particularly true for crystallization in solution, which is an essential part of processes in the chemical and pharmaceutical industries and a major step in physiological and pathological phenomena. There have been significant recent advances in the understanding of the mechanism of nucleation of crystals in solution. The foremost of these are the two-step mechanism of nucleation and the notion of the solution-crystal spinodal. According to the two-step mechanism, the crystalline nucleus appears inside pre-existing metastable clusters of size several hundred nanometers, which consist of dense liquid and are suspended in the solution. While initially proposed for protein crystals, the applicability of this mechanism has been demonstrated for small molecule organic materials, colloids, polymers, and biominerals. This mechanism helps to explain several long-standing puzzles of crystal nucleation in solution: nucleation rates which are many orders of magnitude lower than theoretical predictions, the significance of the dense protein liquid, and others. At high supersaturations typical of most crystallizing systems, the generation of crystal embryos occurs in the spinodal regime, where the nucleation barrier is negligible. The solution-crystal spinodal helps to understand the role of heterogeneous substrates in nucleation and the selection of crystalline polymorphs. Importantly, these ideas provide powerful tools for control of the nucleation process by varying the solution thermodynamic parameters.

Aggregation of amphiphilic polymers in the presence of adhesive small colloidal particles

The interaction of amphiphilic polymers with small colloids, capable to reversibly stick onto the chains, is studied. Adhesive small colloids in solution are able to dynamically bind two polymer segments. This association leads to topological changes in the polymer network configurations, such as looping and cross-linking, although the reversible adhesion permits the colloid to slide along the chain backbone. Previous analyses only consider static topologies in the chain network. We show that the sliding degree of freedom ensures the dominance of small loops, over other structures, giving rise to a new perspective in the analysis of the problem. The results are applied to the analysis of the equilibrium between colloidal particles and star polymers, as well as to block copolymer micelles. The results are relevant for the reversible adsorption of silica particles onto hydrophilic polymers, used in the process of formation of mesoporous materials of the type SBA or MCM, cross-linked cyclodextrin molecules threading on the polymers and forming the structures known as polyrotaxanes. Adhesion of colloids on the corona of the latter induce micellization and growth of larger micelles as the number of colloids increase, in agreement with experimental data.

Caura River basin: Weathering rates, CO2consumption, and chemistry of major and trace elements in an Orinoco River tributary coming from the Precambrian Guayana Shield, Venezuela

This study describes the geochemistry of dissolved elements in the Caura River and gives information about weathering rates and associated CO2 consumption in an Orinoco River subbasin. Physicochemical variables (pH, conductivity, HCO3−, dissolved O2, and temperature), dissolved elements (Na, K, Ca, Mg, Si, Al, Fe, Cu, Mn, Zn, and Cr), total suspended sediments (TSS), and dissolved organic carbon (DOC) concentrations were measured monthly from June 2007 to August 2008 in the Caura River. Major element concentrations (Na, Ca, Mg, and Si) showed an inverse correlation with discharge, whereas K showed high concentration values during the rising waters, probably due to biogenic sources. All these elements are provided mainly from weathering of plagioclases and K feldspars. The weathering rate (riverine flux of dissolved major cations and SiO2 derived from weathering per unit area) and the CO2 consumption rate in the Caura basin (15.4 tons km−2 yr−1 and 1.1 × 105 mol km−2 yr−1, respectively) were higher than those reported for the Orinoco basin and other black water river basins. This fact can be due to several factors such as lithology (volcanic rocks), high runoff, and the presence of organic acids, which can enhance the chemical weathering. The variability of the trace elements showed a different behavior than major elements. Fe and Al concentrations were correlated with DOC. Dissolved Mn content was correlated with pH, whereas the low concentrations of Cu and Cr are possibly associated with the low content of small size organic colloids. The high values of Zn observed during the decreasing stage suggest biogenic input of Zn to river waters.

Self-assembly in binary mixtures of dipolar colloids: Molecular dynamics simulations

Dipolar colloid particles tend to align end-to-end and self-assemble into micro- and nanostructures, including gels and cocrystals depending on external conditions. We use molecular dynamics computer simulation to explore the phase behavior including formation, structure, crystallization, and/or gelation of binary systems of colloid particles with permanent dipole moments. Particle-particle interactions are modeled with a discontinuous potential. The phase diagrams of an equimolar binary mixture of dipolar colloid particles with different diameter ratios and different dipole moment ratios are calculated in the temperature-volume fraction plane. Several types of phases are found in our simulations: ordered phases including face centered cubic (fcc), hexagonal-close packed (hcp), and body-centered tetragonal (bct) at high volume fractions, and fluid, string-fluid, and gel phases at low volume fractions. We also find several coexistence regions containing ordered phases including fcc(a)+fcc(b), fcc(a)+hcp(b), hcp(a)+hcp(b), bct(a)+bct(b), and bct(a)+bct(b)+large voids where a and b are the two species. Two novel aspects of our results are the appearance of a bicontinuous gel consisting of two interpenetrating networks--one formed by chains of particles with high dipole moment and the other formed by chains of particles with low dipole moment, and cocrystals of large and small dipolar colloid particles.

Hydrogen-Bond-Induced Heteroassembly in Binary Colloidal Systems

A new binary colloidal system is designed with each colloidal component being able to exclusively interact with the colloids of the second component, respectively. The colloids are based on cross-linked polystyrene and polymerized by means of surfactant-free emulsion polymerization with either 4-hydroxyl styrene or 4-vinyl pyridine as comonomers. The comonomers are selected to decorate the colloids with complementary H-bond donors or acceptors. Characterization of the colloids by light scattering in CHCl(3) results in particle radii covering a regime of 130 nm < R < 270 nm and indicates a narrow particle size distribution for all prepared samples. The colloids are slightly swollen compared to their state in H(2)O. The corresponding size ratio expressed as the radius of the small colloids divided by the radius of the large colloids in CHCl(3) extends over a regime of 0.52 < R(S)/R(L) < 0.85. IR analysis indicates strong hydrogen bonds between a colloidal component and the complementary molecular functions, that is, phenol or pyridine. If both colloidal components are directly combined as suspension in CHCl(3) a fast heteroaggregation is observed. This aggregation slows down and becomes accessible to an analysis by means of time-resolved static light scattering if the suspensions get sufficiently dilute. Fast aggregation can be totally inhibited if capping agents like phenol to cap the 4-vinyl pyridine functions are added as highly concentrated solutions. Dried samples of those binary suspensions equilibrated with an appropriate amount of phenol show the first indication for an ordered binary assembly.

Void superlattice formation in electron irradiated CaF 2: Theoretical analysis

CaF 2 is widely adopted as deep-UV window material and thin film optical coating. The void superlattice was observed experimentally under electron irradiation at room temperature. We performed kinetic Monte Carlo (kMC) simulations of the initial stages of the process when short- and intermediate-range order of defects in small Ca colloids and larger interstitial aggregates (F 2 gas voids) is created. The kMC model includes fluorine interstitial–vacancy pair creation, defect diffusion, similar defect attraction and dissimilar defect recombination. Special attention is paid to the statistical analysis of the defect aggregate distribution functions under different conditions (dose rate, defect migration and recombination rates). These simulations demonstrate that under certain conditions the dissimilar aggregate recombination is strongly suppressed which stimulates growth of mobile interstitial aggregates that is a precondition for further void ordering into a superlattice.

Surface Decoration of ZnO Nanorod Arrays by Electrophoresis in the Au Colloidal Solution Prepared by Laser Ablation in Water

A simple and green strategy is presented to decorate ZnO nanorod array, based on electrophoresis deposition in the Au colloidal solution prepared by laser ablation in water and subsequent further laser irradiation. The surface of nanorods is homogeneously decorated with Au nanoparticles. The Au nanoparticles have good interfacial connection and strong binding with ZnO nanorods. The decoration morphology can be easily controlled by the size of Au colloids. Further experiments have revealed that suitable electrophoretic potential, small Au colloid's size, and enough inter-nanorod's spacing are crucial to formation of a homogeneous and strong surface decoration. Such Au nanoparticle-decorated ZnO nanorod array is functionalized and exhibits excellent surface-enhanced Raman scattering performance and shows the possibility of molecule-level detection. This study provides a new opportunity for the controllable surface modification of 1D semiconductor nanostructures and deepens the understanding of the physical mechanism of electrophoretic deposition.

Surface-Enhanced Resonance Raman Scattering and Visible Extinction Spectroscopy of Copper Chlorophyllin: An Upper Level Chemistry Experiment

Advanced chemistry students are introduced to surface-enhanced resonance Raman scattering (SERRS) by studying how sodium copper chlorophyllin (CuChl) adsorbs onto silver colloids (CuChl/Ag) as a function of pH. Using both SERRS and visible extinction spectroscopy, the extent of CuChl adsorption and colloidal aggregation are monitored. Initially at pH ∼10, the colloids possess an overall negative surface charge, preventing attraction. Surface-enhanced Raman scattering (SERS) is not detected at that pH because the relatively small colloids do not possess a surface plasmon in resonance with the laser excitation frequency (633 nm). Once the solution pH decreases slightly, colloidal clusters form and SERRS is detected. As the pH is lowered to a value of 4 or 3, protonation of CuChl results in colloidal aggregation and precipitation. If adsorption and aggregation are halted by adding H2SO4(aq) and then NaOH(aq), an intense SERRS signal is steadily detected from acidic pH (about 4), back to the initial basic pH (about 10).

An iron budget during the natural iron fertilisation experiment KEOPS (Kerguelen Islands, Southern Ocean)

Abstract. Total dissolvable iron (TDFe) was measured in the water column above and in the surrounding of the Kerguelen Plateau (Indian sector of the Southern Ocean) during the KErguelen Ocean Plateau compared Study (KEOPS) cruise. TDFe concentrations ranged from 0.90 to 65.6 nmol L−1 above the plateau and from 0.34 to 2.23 nmol L−1 offshore of the plateau. Station C1 located south of the plateau, near Heard Island, exhibited very high values (329–770 nmol L−1). Apparent particulate iron (Feapp), calculated as the difference between the TDFe and the dissolved iron measured on board (DFe) represented 95±5% of the TDFe above the plateau, suggesting that particles and refractory colloids largely dominated the iron pool. This paper presents a budget of DFe and Feapp above the plateau. Lateral advection of water that had been in contact with the continental shelf of Heard Island seems to be the predominant source of Feapp and DFe above the plateau, with a supply of 9.7±3.6×106 and 8.3±11.6×103 mol d−1, respectively. The residence times of 1.7 and 48 days estimated for Feapp and DFe respectively, indicate a rapid turnover in the surface water. A comparison between Feapp and total particulate iron (TPFe) suggests that the total dissolved fraction is mainly constituted of small refractory colloids. This fraction does not seem to be a potential source of iron to the phytoplankton in our study. Finally, when taking into account the lateral supply of dissolved iron, the seasonal carbon sequestration efficiency was estimated at 154 000 mol C (mol Fe)−1, which is 4-fold lower than the previously estimated value in this area but still 18-fold higher than the one estimated during the other study of a natural iron fertilisation experiment, CROZEX.

Charge renormalization of nanoparticles immersed in a molecular electrolyte

The renormalization of the electric charge of nanoparticles (small colloids) at infinite dilution immersed in a supporting electrolyte containing molecular ions is studied here using a simple model. The nanoparticles are represented by charged spheres of finite diameter, the anions are assumed to be pointlike, and the cations are modeled as two identical charged points connected by a rigid rod. The static structure of this model system is determined using the reference interaction site model equations with suitable closure relations and the renormalized charges are analyzed employing the dressed interactions site theory approach. It is found that for a wide range of ionic strengths these renormalized charges are clearly dependent on the length of the cations for nanoparticles with negative bare charge, but this dependence is practically negligible for nanoparticles with positive bare charges. In the limit of zero cation length and small nanoparticle charges the standard Derjaguin-Landau-Verwey-Overbeek model renormalization is recovered. A brief account of the structural and thermodynamic properties of the model molecular electrolyte is also provided.

Hydrodynamic interaction of two colloids in nonadsorbing polymer solutions

The hydrodynamic interaction between two colloids mediated by non-adsorbing polymer chains is considered for spherical colloids moving along the symmetric line. We present a resistance analysis and determine the mobility function that incorporates the polymer depletion effect. The hydrodynamic friction is calculated by solving the Stokes equation with non-uniform viscosity using the vorticity-stream function method and a bispherical coordinate transformation. The numerical results show the effective viscosity asymptotically approaches the single sphere limit of Fan et al. (T.-H. Fan, B. Xie and R. Tuinier, Phys. Rev. E., 2007, 76, 051405) for a large interparticle distance. As the particles get closer the effective viscosity decreases and finally approaches the lubrication limit, where the friction equals that of two close-approached spheres in a pure solvent. The flow analysis shows that the circulation pattern, a characteristic for the presence of the depletion layer, expands upon approach of the particles. The pressure contribution to the total drag force is determined by a competition between the lubrication force and the apparent slip effect caused by overlap of the depletion layers. The friction of the single sphere limit is only attained in the limit of an extremely small colloid volume fractions. Our results help rationalize the long-time relative diffusivity of Brownian particles in polymer solutions and this is important for a better understanding of the depletion-induced demixing kinetics.