Thin film formation of silica nanoparticle/lipid composite films at the fluid-fluid interface

We report a new and simple method for the formation of thin films at the interface between aqueous silica Ludox dispersions and lipid solutions in decane. The lipids used are stearic acid, stearyl amine, and stearyl alcohol alongside silica Ludox nanoparticle dispersions of varying pH. At basic pH thin films consisting of a mixture of stearic acid and silica nanoparticles precipitate at the interface. At acidic and neutral pH we were able to produce thin films consisting of stearyl amine and silica particles. The film growth was studied in situ with interfacial shear rheology. In addition to that, surface pressure isotherm and dynamic light scattering experiments were performed. The films all exhibit strong dynamic rheological moduli, rendering them an interesting material for applications such as capsule formation, surface coating, or as functional membranes.     

Microfluidic approaches to bacterial biofilm formation

Bacterial biofilms-aggregations of bacterial cells and extracellular polymeric substrates (EPS)-are an important subject of research in the fields of biology and medical science. Under aquatic conditions, bacterial cells form biofilms as a mechanism for improving survival and dispersion. In this review, we discuss bacterial biofilm development as a structurally and dynamically complex biological system and propose microfluidic approaches for the study of bacterial biofilms. Biofilms develop through a series of steps as bacteria interact with their environment. Gene expression and environmental conditions, including surface properties, hydrodynamic conditions, quorum sensing signals, and the characteristics of the medium, can have positive or negative influences on bacterial biofilm formation. The influences of each factor and the combined effects of multiple factors may be addressed using microfluidic approaches, which provide a promising means for controlling the hydrodynamic conditions, establishing stable chemical gradients, performing measurement in a high-throughput manner, providing real-time monitoring, and providing in vivo-like in vitro culture devices. An increased understanding of biofilms derived from microfluidic approaches may be relevant to improving our understanding of the contributions of determinants to bacterial biofilm development.     

Metal-catalysed approaches to amide bond formation

Amongst the many ways of constructing the amide bond, there has been a growing interest in the use of metal-catalysed methods for preparing this important functional group. In this tutorial review, highlights of the recent literature have been presented covering the key areas where metal catalysts have been used in amide bond formation. Acids and esters have been used in coupling reactions with amines, but aldehydes and alcohols have also been used in oxidative couplings. The use of nitriles and oximes as starting materials for amide formation are also emerging areas of interest. The use of carbon monoxide in the transition metal catalysed coupling of amines has led to a powerful methodology for amide bond formation and this is complemented by the addition of an aryl or alkenyl group to an amide typically using palladium or copper catalysts.     

Preparation and properties of biocompatible polymer-grafted silica nanoparticle

Grafting of biocompatible polymer onto the surface of silica nanoparticles was achieved by radical graft polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC), initiated by azo groups previously introduced onto the surface or by a system consisting of Mo(CO)₆ and trichloroacetyl groups on the silica surface. Both of these systems have the ability to initiate graft polymerization of MPC, resulting in the formation of poly(MPC)-grafted silica, but the percentage of poly(MPC) grafting for the latter initiating system was much higher than that of the former. The amount of moisture that could be adsorbed onto the silica surface was found to increase with increasing poly(MPC) grafting. This indicates that grafting of poly(MPC) onto the silica surface markedly increases the hydrophilic nature of the surface. The contact angle of water in composites prepared from poly(vinyl alcohol) and poly(MPC)-grafted silica was found to decrease with increasing poly(MPC)-grafted silica content. When poly(MPC)-grafted silica was added to water containing a small amount of chloroform, it was found to act as stabilizer for droplets of chloroform. In addition, according to tests by the Lee-White method, poly(MPC)-grafted silica shows non-thrombogenic characteristics.     

Novel fluorescent silica nanoparticle probe for ultrasensitive immunoassays

The preparation and utilization of a novel particulate label based on fluorescent hybrid silica (FHS) nanoparticles are reported in this article. These nanoparticles have shown several unique advantages over existing dye molecules, quantum dots, and latex-based fluorescent particles in easy preparation, good photostability and high sensitivity. A high molar ratio of the fluorescent molecules present in the core to biomolecules on the particle surface was achieved by using the well-developed silica surface immobilization chemistry for biomolecular linking. A fluoroimmunoassay method for detecting trace level Hepatitis B Surface Antigen (HBsAg) was developed. The calibration graph for HBsAg was linear over the range 0.5-220 ng/ml with a detection limit of 0.1 ng/ml. The sensitivity is greatly increased when compared with the corresponding immunoassay performed with direct fluorophore labeling. The present work shows that these FHS nanoparticles are high-quality markers for biochemical assays.     

Biomagnetic nanoparticle formation and application

Magnetospirillum sp. AMB-1 is a bacterium that synthesizes intracellular particles of magnetite (Fe₃O₄). A magA gene required for the synthesis of bacterial magnetic particles (BMPs) was isolated from this strain and its gene product (MagA protein) was characterized as an iron transport protein. Intracellular localization analysis of the MagA protein using magA–Luc fusion proteins showed that MagA protein is localized on the surface of the lipid bilayer covering the BMPs. One particular BMP-associated protein, designated MpsA, was also purified from this strain and characterized. By the fusion-protein method using mpsA-luc genes, it was demonstrated that Mps-protein is preferentially partitioned onto the BMP membrane. Furthermore, application of BMPs to immunoassay is also described.     

Electrostatically tuned interactions in silica microsphere-polystyrene nanoparticle mixtures

We explore the generality of nanoparticle haloing as a novel colloidal stabilization mechanism in binary mixtures of silica microspheres and polystyrene nanoparticles. By selectively tuning their electrostatic interactions, both the initial microsphere stability and the role of nanoparticle additions are varied. Adsorption isotherm and zeta potential measurements indicate that highly charged nanoparticles exhibit a weak (haloing) association with negligibly charged microspheres, whereas they either strongly adsorb onto oppositely charged or are repelled by like-charged microsphere surfaces, respectively. Bulk sedimentation and confocal scanning fluorescence microscopy reveal that important differences in system stability emerge depending on whether the added nanoparticles serve as haloing, bridging, or depletant species.     

Fluorescent quantification of amino groups on silica nanoparticle surfaces

Functionalization of the surfaces of silica particles is often the first step in their various applications. An improved heterogeneous Fmoc-Cl fluorescent assay using an aqueous solution was developed to detect the number of amino groups on solid-phase supports. The fluorescent Fmoc-Cl method is 50-fold more sensitive than the current UV assay using an organic solvent. This method, together with the homogeneous fluorescamine and OPA assays, is used to detect amino groups on the silica particle surface. The accuracy and effect factors of these methods were examined and the assays were optimized. The results showed that the amine groups on silica particles can produce stronger fluorescence than small amine molecules in solution, because the porous structure of the particle surface is a more hydrophobic environment. The number of active amino groups that can be conjugated with biomolecules is much less than the total number of amino groups on the silica particle. Compared with physical methods, chemical assays involving direct reaction with amino groups would furnish the closest result to the number of active amino groups on the particle surface.     

Immobilization of capsaicin onto silica nanoparticle surface and stimulus properties of the capsaicin‐immobilized silica

To prepare silica nanoparticle having biorepellent activity, the immobilization of capsaicin onto hyperbranched poly(amidoamine) (PAMAM)‐grafted silica was investigated. Grafting of PAMAM onto a silica surface was achieved in a solvent‐free dry system using PAMAM dendrimer synthesis methodology. The immobilization of capsaicin was achieved by the reaction of hydroxyl groups of capsaicin with isocyanate groups of Silica‐PAMAM, which were introduced by the reaction of terminal amino groups of Silica‐PAMAM with hexamethylene diisocyanate. The immobilization of capsaicin was confirmed by thermal decomposition GC‐MS. The amount of capsaicin immobilized onto PAMAM‐grafted silica was determined to be 0.10 mmol/g. Capsaicin‐immobilized Silica‐PAMAM (Silica‐PAMAM‐Cap) was dispersed uniformly in water and Tyrode solution. Stimulus activity of Silica‐PAMAM‐Cap was estimated using two stimulus tests, that is a magnus test and a paw licking test, to sensory nerve of mice. As the result of magnus test, it was found that the Silica‐PAMAM‐Cap shows stimulus activity. It was found that elution of capsaicin could be depressed by immobilizing capsaicin onto Silica‐PAMAM from the result of paw licking test. In addition, the stimulus property of Silica‐PAMAM‐Cap to the human skin could be observed and it was found that Silica‐PAMAM‐Cap had acrid taste. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1800–1805, 2010     

Silver nanoparticle growth in 3D-hexagonal mesoporous silica films

The 3D-hexagonal mesoporous films are used as templates to grow uniform silver nanoparticles. The grafting of hydrophobic groups at the pore surface, significantly slows down the silver ion diffusion, anchoring small silver clusters in micropores and leading to organized domains of silver particles in mesopores with a narrow size distribution.     

Tuning the self-assembled monolayer formation on nanoparticle surfaces with different curvatures: investigations on spherical silica particles and plane-crystal-shaped zirconia particles

The ordering of dodecyl-chain self-assembled monolayers (SAM) on different nanoscopic surfaces was investigated by FT-IR studies. As model systems plane-crystal-shaped ZrO(2) nanoparticles and spherical SiO(2) nanoparticles were examined. The type of capping agent was chosen dependent on the substrate, therefore dodecylphosphonic acid and octadecylphosphonic acid were used for ZrO(2) and dodecyltrimethoxysilane for SiO(2) samples. The plane ZrO(2) nanocrystals yielded more ordered alkyl-chain structures whereas spherical SiO(2) nanoparticles showed significantly lower alkyl-chain ordering. Submicron-sized silica spheres revealed a significantly higher alkyl chain ordering, comparable to an analogously prepared SAM on a non-curved plane oxidized Si-wafer. In the case of ZrO(2) nanocrystals an intense alkyl-chain alignment could be disturbed by decreasing the grafting density from the maximum of 2.1 molecules/nm(2) through the variation of coupling agent concentration to lower values. Furthermore, the co-adsorption of a different coupling agent, such as phenylphosphonic acid for ZrO(2) and phenyltrimethoxysilane for SiO(2), resulted in a significantly lower alkyl-chain ordering for ZrO(2) plane crystals and for large SiO(2) spherical particles at high grafting density. An increasing amount of order-disturbing molecules leads to a gradual decrease in alkyl-chain alignment on the surface of the inorganic nanoparticles. In the case of the ZrO(2) nanoparticle system it is shown via dynamic light scattering (DLS) that the mixed monolayer formation on the particle surface impacts the dispersion quality in organic solvents such as n-hexane.     

Phthalocyanine nanoparticle formation in supersaturated solutions

Self-organization of molecules in solution is an important natural and synthetic process, in particular for the preparation of nanomaterials. However, the mechanism of growth for solution-based nanoparticle formation is not always well understood. We present results that clarify these mechanisms in solutions of magnesium phthalocyanine in which the self-organization is induced by addition of a miscible nonsolvent. From simultaneous measurements of the sizes of the growing nanoparticles by photon correlation spectroscopy and the molecular concentration by absorption and fluorescence spectroscopy, we have found that the particles do not grow by molecular diffusion to the surfaces. These results suggest the importance of unstable clusters in the growth process. We also observed a strong dependence of the particle size on the initial concentration which we attribute to effects of the curvature of the solubility curve.     

Determination of trace silica in highly purified water based on delayed quenching of Rhodamine B through nanoparticle formation with molybdosilicate

The development of a highly sensitive analytical method for trace silica is an urgent necessity for the real-time monitoring of highly purified water used in the semiconductor industry. However, there are no reports of a simple yet sensitive method for the determination of trace silica. Here we describe the delayed quenching phenomenon of Rhodamine B cation caused by nanoparticle formation with molybdosilicate ions in aqueous solution and its application to the one-step determination of trace silica at ppt to low ppb levels. We found that the quenching takes place over several minutes and the quenching time is dependent on the concentration of silica. The measurements made by a dynamic light scattering particle size analyzer indicated that the diameter of the particles were at nanometer levels. The detection limit was found to be 34 ng dm(-3) Si (1.2 x 10(-9) mol dm(-3)). The average quenching time for 1 microg dm(-3) was 239 s with an RSD of 2.2% (n= 7). The proposed method has been successfully applied to distilled and highly purified water samples. There was good agreement between the results obtained by the proposed method and those by ICP-three dimensions quadrupole MS/MS with 11-fold evaporation concentration. The main point of this method is that in the trace determination of silica, the signal is larger at lower concentrations. The advantages of the proposed method are that it can be used as real-time monitoring for trace silica in highly purified water, and will be a great aid to industries in which the quality control of water is crucial.     

Remarkable catalytic activity of silica nanoparticle in the bis-Michael addition of active methylene compounds to conjugated alkenes

We have demonstrated the remarkable catalytic activity of silica nanoparticles (NPs) in the unusual bis-Michael addition of active methylene compounds to conjugated alkenes at room temperature. The catalyst silica NPs were reused up to seven runs without appreciable loss of catalytic activity.     

Synthesis of porous hollow silica nanostructures using hydroxyapatite nanoparticle templates

Porous hollow spherical and rod-like silica nanoparticles were obtained via a surfactant templating method adopting hydroxyapatite (HAp) nanoparticles as an etchable core material.     

Controlled, simultaneous assembly of polyethylenimine onto nanoparticle silica colloids

A novel precision-assembly methodology is described on the basis of the controlled, simultaneous assembly (CSA) of a core nanoparticle substrate and polyelectrolyte solutions. The method is capable of assembly rates at least as fast as 10(16) core particles s(-1) L(-1) and affords concentrated suspensions of stable colloids with an adsorbed polyelectrolyte. The resulting dispersions are highly homogeneous, have a low viscosity and narrow particle-size distribution, and are stable colloids, even at solid concentrations of at least 33 wt %. The adsorption isotherm and the saturation adsorption for polyethylenimine (PEI) assemblies onto a 15 nm silica colloid have been evaluated with 1H NMR spectroscopy. The saturation adsorption is highly dependent upon the pH at assembly and is given by the equation PEIa (micromol m(-2)) = 1.73pH - 1.89, R2 = 0.986, where micromoles refers to the concentration of the EI monomer. The saturation concentration increases from 6.8 micromol m(-2) at pH 5.0 to 13.7 micromol m(-2) at pH 9.0. The adsorbed polyelectrolyte may be cross-linked and thereby permanently fixed to the colloid surface to prepare nanoparticle-polyelectrolyte colloidal assemblies having enhanced colloid stability, high homogeneity, and a high fraction (>80%) of permanently adsorbed polyelectrolyte. These assemblies are stable at physiological pH and ionic strength and may represent ideal substrates for bioconjugation and, ultimately, the design of nanocarriers for in vivo applications.