Nonporous Silica Nanoparticles Research Articles

Fluorescent non-porous silica nanoparticles for long-term cell monitoring: Cytotoxicity and particle functionality

Inorganic nanoparticles such as silica particles offer many exciting possibilities for biomedical applications. However, the possible toxicity of these particles remains an issue of debate that seriously impedes their full exploitation. In the present work, commercially available fluorescent silica nanoparticles 25, 45 and 75nm in diameter optimized for cell labelling (C-Spec® particles) are evaluated with regard to their effects on cultured cells using a novel multiparametric setup. The particles show clear concentration and size-dependent effects, where toxicity is caused by the number and total surface area of cell-associated particles. Cell-associated particles generate a short burst of oxidative stress that, next to inducing cell death, affects cell signalling and impedes cell functionality. For cell labelling purposes, 45nm diameter silica particles were found to be optimally suited and no adverse effects were noticeable at concentrations of 50μgml−1 or below. At this safe concentration, the particles were found to still allow fluorescence tracking of cultured cells over longer time periods. In conclusion, the data shown here provide a suitable concentration of silica particles for fluorescent cell labelling and demonstrate that at safe levels, silica particles remain perfectly suitable for fluorescent cell studies.

Catalytic behavior of carbonic anhydrase enzyme immobilized onto nonporous silica nanoparticles for enhancing CO2 absorption into a carbonate solution

Nonporous, nano-sized support materials can offer a large external surface area for enzyme immobilization and improve the activity of the immobilized enzyme by eliminating internal diffusion of a substrate. In this study, nonporous silica nanoparticles with different sizes were synthesized by a flame spray pyrolysis (FSP) method and used as support materials for immobilization of the carbonic anhydrase (CA) enzyme for a CO2 capture application. The immobilization conditions, such as reaction time, pH, and initial enzyme concentration, were investigated to obtain both high enzyme loading and activity. The effects of temperature and pH on the immobilized enzyme's catalytic activity were investigated. Through immobilization, the CA enzymes remained active at the elevated temperature and pH conditions expected during CO2 absorption from the flue gases. At 50°C and pH 10.5, the activities of the immobilized enzymes were about three times that of the free enzyme. Classic Danckwerts theory for absorption with reaction was applied to calculate the enzymatic kinetics for CO2 absorption. The enzyme's thermal stability also was significantly improved by the immobilization. Compared to its free enzyme counterpart, the half-life time of the immobilized enzyme was increased by up to 4.4 times over a 30-day test period at 50°C.

Multifunctional silica nanoparticles for optical and magnetic resonance imaging

The surface of spherical, nonporous silica nanoparticles (SiO2-NPs) was modified with gadolinium (Gd) complexes, fluorophores, and cell-penetrating peptides to achieve multifunctionality on a single particle. The Gd surface concentrations were 9-16 μmol/g resulting in nanomaterials with high local longitudinal and transversal relaxivities (~1×10(5) and ~5×10(5) /mm/s/NP, respectively). Rapid cellular uptake was observed in vitro; however, larger extracellular agglomerates were also formed. In vivo administration revealed a fast distribution throughout the body followed by a nearly complete disappearance of fluorescence in all organs except the lungs, liver, and spleen after 24 h. Such NPs have the potential to serve as efficient multimodal probes in molecular imaging.

Fabrication of a novel thin-film nanocomposite (TFN) membrane containing MCM-41 silica nanoparticles (NPs) for water purification

A thin-film nanocomposite (TFN) membrane containing porous MCM-41 silica nanoparticles (NPs) was prepared by the in situ interfacial polymerization (IP) process. Aqueous m-phenyl diamine (MPD) and organic trimesoyl chloride (TMC)-NPs mixture solutions were used in the IP process. Porous MCM-41 (∼100nm) and non-porous spherical silica NPs (∼100nm) were synthesized and used as the fillers to fabricate the TFN membrane at concentrations ranging from 0 to 0.1wt%. The membranes were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy, and their performances were evaluated based on the water permeability and salt rejection. Results indicated that the MCM-41 NPs dispersed well in polyamide (PA) thin-film layer and improved membrane performances under optimal concentrations. By increasing concentration of MCM-41 NPs, hydrophilicity, roughness and zeta potential of TFN membranes all increased. Notably, the permeate water flux increased from 28.5±1.0 to 46.6±1.1L/m2h with the incorporation of MCM-41 NPs, while maintaining high rejections of NaCl and Na2SO4 (97.9±0.3% and 98.5±0.2%, respectively). A comparison between the membranes with non-porous silica NPs (S-TFN) and with the porous MCM-41 NPs (M-TFN) suggested that the internal pores of MCM-41 NPs contributed significantly to the increase of water permeability.

Hybrid Nanomaterials that Mimic the Food Effect: Controlling Enzymatic Digestion for Enhanced Oral Drug Absorption

Easily digested: SiO2–lipid hybrid microparticles with specific nanostructured interiors were generated from submicrometer-sized emulsion templates based on mesoporous and non-porous silica nanoparticles. These functional lipid-based microparticles can be used to mimic the pharmaceutical food effect and enhance drug absorption by controlling the enzymatic digestion of lipid colloids (see scheme; ○ oil solution, ▴ lipid–nanoparticle hybrid, □ lipid encapsulated in hybrid). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Preparation of Colloidal Mesoporous Silica Nanoparticles with Different Diameters and Their Unique Degradation Behavior in Static Aqueous Systems

The degradation of colloidal mesoporous silica nanoparticles (CMPS) is quite important for the design of stable catalyst supports and biodegradable drug delivery systems carriers. The degradation of various silica nanoparticles in static aqueous systems was investigated. The condition was achieved through the use of a dialysis tube. Four types of CMPS with different particle diameters (ca. 20–80 nm) were newly prepared from tetraalkoxysilanes (Si(OR)4, R = Me, Et, Pr, and Bu) at different hydrolysis rates by a one-pot synthesis. Larger particles were formed by using tetraalkoxysilanes at slower hydrolysis rates because particle growth dominates nucleation. The degradation of CMPS is independent of diameter differences. The degradation rate of CMPS is higher than that of colloidal nonporous silica nanoparticles with smaller diameters because of the presence of mesopores. CMPS are also more degradable than aggregated CMPS because of colloidal dispersity. Moreover, it was confirmed for the first time that th...

Synthesis, characterization and examination of Gd[DO3A-hexylamine]-functionalized silica nanoparticles as contrast agent for MRI-applications

Spherical, nonporous and monodisperse silica nanoparticles (NPs) with a diameter of about 100nm were synthesized and covalently functionalized with lanthanoid(III) (Ln=Gd or Y) chelate complexes, which serve as contrast agents (CAs) for magnetic resonance imaging (MRI). The materials were fully characterized after each synthetic step by different analytical methods, such as dynamic light scattering, scanning electron microscopy, DRIFT and NMR spectroscopy, thermogravimetry and elemental analysis, as well as zetapotential measurements. High surface concentrations of Gd(III) complexes (up to 50μmolg−1) were determined by ICP-AES and T1-measurements, respectively. MRI experiments show the typical concentration-dependent increase of the longitudinal relaxation rate. T1-weighted images of samples with more than 25μg NPs per 100μL agar display a clear contrast enhancement in the agar layer. The transverse relaxivities r2 of the materials are significantly higher than r2 of the corresponding free Gd(III) complexes in water and medium, whereas the longitudinal relaxivities r1 are slightly increased. Due to the high loading of Gd(III) complexes, the relaxivities per particle are remarkably high (up to 2.78×105mM−1s−1 for r1). Thus, new hybrid materials, based on nonporous silica NPs with high local relaxivity values were synthesized, which can serve as very effective CAs for MRI.

Pyrolysis of Phenethyl Phenyl Ether Tethered in Mesoporous Silica. Effects of Confinement and Surface Spacer Molecules on Product Selectivity

There has been expanding interest in exploring porous metal oxides as a confining environment for organic molecules resulting in altered chemical and physical properties including chemical transformations. In this paper, we examine the pyrolysis behavior of phenethyl phenyl ether (PPE) confined in mesoporous silica by covalent tethers to the pore walls as a function of tether density and the presence of cotethered surface spacer molecules of varying structure (biphenyl, naphthyl, octyl, and hexadecyl). The PPE pyrolysis product selectivity, which is determined by two competitive free-radical pathways cycling through the two aliphatic radical intermediates (PhCH·CH(2)OPh and PhCH(2)CH·OPh), is shown to be significantly different from that measured in the liquid phase as well as for PPE tethered to the exterior surface of nonporous silica nanoparticles. Tailoring the pore surface with spacer molecules further alters the selectivity such that the PPE reaction channel involving a molecular rearrangement (O-C phenyl shift in PhCH(2)CH·OPh), which accounts for 25% of the products in the liquid phase, can be virtually eliminated under pore confinement conditions. The origin of this change in selectivity is discussed in the context of steric constraints on the rearrangement path inside the pores, surface and pore confinement effects, pore surface curvature, and hydrogen bonding of PPE with residual surface silanols supplemented by nitrogen physisorption data and molecular dynamics simulations.

Synthesis of magnetic, fluorescent and mesoporous core-shell-structured nanoparticles for imaging, targeting and photodynamic therapy

A synthetic method to prepare novel multifunctional core-shell-structured mesoporous silica nanoparticles for simultaneous magnetic resonance (MR) and fluorescence imaging, cell targeting and photosensitization treatment has been developed. Superparamagnetic magnetite nanoparticles and fluorescent dyes are co-encapsulated inside nonporous silica nanoparticles as the core to provide dual-imaging capabilities (MR and optical). The photosensitizer molecules, tetra-substituted carboxyl aluminum phthalocyanine (AlC4Pc), are covalently linked to the mesoporous silica shell and exhibit excellent photo-oxidation efficiency. The surface modification of the core-shell silica nanoparticles with folic acid enhances the delivery of photosensitizers to the targeting cancer cells that overexpress the folate receptor, and thereby decreases their toxicity to the surrounding normal tissues. These unique advantages make the prepared multifunctional core-shell silica nanoparticles promising for cancer diagnosis and therapy.

Using nanocomposite materials technology to understand and control reverse osmosis membrane compaction

Composite reverse osmosis (RO) membranes were formed by interfacial polymerization of polyamide thin films over pure polysulfone and nanocomposite-polysulfone support membranes. Nanocomposite support membranes were formed from amorphous non-porous silica and crystalline microporous zeolite nanoparticles. For each hand-cast membrane, water flux and NaCl rejection were monitored over time at two different applied pressures. Nanocomposite-polysulfone supported RO membranes generally had higher initial permeability and experienced less flux decline due to compaction than pure polysulfone supported membranes. In addition, observed salt rejection tended to increase as flux declined from compaction. Cross-sectional SEM images verified significant reduction in thickness of pure polysulfone supports, whereas nanocomposites better resisted compaction due to enhanced mechanical stability imparted by the nanoparticles. A conceptual model was proposed to explain the mechanistic relationship between support membrane compaction and observed changes in water flux and salt rejection. As the support membrane compacts, skin layer pore constriction increased the effective path length for diffusion through the composite membranes, which reduced both water and salt permeability identically. However, experimental salt permeability tended to decline to a greater extent than water permeability; hence, the observed changes in flux and rejection might also be related to structural changes in the polyamide thin film.

Impacts of Mesoporous Silica Nanoparticle Size, Pore Ordering, and Pore Integrity on Hemolytic Activity

This paper uses the measure of hemolysis to evaluate the toxicity of nonporous and porous silica nanoparticles with varied sizes and investigates the effects of porous structure and integrity on the nanoparticle-cell interaction. The results show that both nonporous and porous silica cause red blood cell membrane damage in a concentration- and size-dependent manner. In the case of mesoporous silica nanoparticles, the size-dependent hemolysis effect is only present when the nanoparticles have long-range ordered porous structure, revealing that pore structure is critical in cell-nanoparticle interactions. Mesoporous silica nanoparticles show lower hemolytic activity than their nonporous counterparts of similar size, likely due to fewer silanol groups on the cell-contactable surface of the porous silica nanoparticles. The extent of hemolysis by mesoporous silica nanoparticles increases as the pore structure is compromised by mild aging in phosphate-buffered solutions, initiating mesopore collapse. The pore integrity of mesoporous silica nanoparticles is examined by TEM, XRD, N(2) adsorption-desorption isotherms, and quantification of dissolved silica. In these nanoparticles, pore stability is clearly an important factor in determining the hemolytic activity; further work demonstrates that nanoparticle-induced hemolysis can be eliminated by modifying the silanol surface with a poly(ethylene glycol) coating.

Nanoparticles of Mesoporous SO3H‐Functionalized Si‐MCM‐41 with Superior Proton Conductivity

Nanometer-sized mesoporous silica particles of around 100-nm diameter functionalized with a large amount of sulfonic acid groups are prepared using a simple and fast in situ co-condensation procedure. A highly ordered hexagonal pore structure is established by applying a pre-hydrolysis step in a high-dilution synthesis approach, followed by adding the functionalization agent to the reaction mixture. The high-dilution approach is advantageous for the in situ functionalization since no secondary reagents for an effective particle and framework formation are needed. Structural data are determined via electron microscopy, nitrogen adsorption, and X-ray diffraction, proton conductivity values of the functionalized samples are measured via impedance spectroscopy. The obtained mesoporous SO(3)H-MCM-41 nanoparticles demonstrate superior proton conductivity than their equally loaded micrometer-sized counterparts, up to 5 x 10(-2) S cm(-1). The mesoporosity of the particles turns out to be very important for effective proton transport since non-porous silica nanoparticles exhibit worse efficient proton transport, and the obtained particle size dependence might open up a new route in rational design of highly proton conductive materials.

Mesoporous carbons prepared by nano-casting with meso- or non-porous silica nanoparticles

Mesoporous carbons were obtained by sequential nano-casting using the following hard templates: (i) mesoporous silica nanospheres with MCM-41 or MCM-48 analogous structure; (ii) non-porous silica nanospheres and (iii) pyrogenic silica (Aerosil 200). These silica templates (patrix) were impregnated with sucrose, carbonized at 800 oC under nitrogen atmosphere and finally the silica dissolved with hydrofluoric acid. It was observed that the specific surface area of the carbon matrixes can be enhanced reducing the diameter of the silica nanospheres or the distance between them by agglomeration prior to the impregnation of the silica patrix with sucrose. Mesoporous carbons with specific surface areas higher than 500 m2 g-1 were obtained using mesoporous silica spheres. In this case, the carbon matrixes contain mesopores with a narrow pore size distribution and with diameters in the order of the wall thickness of the mesoporous silica used as hard template.

Redox-Active Silica Nanoparticles. Part 1. Electrochemistry and Catalytic Activity of Spherical, Nonporous Silica Particles with Nanometric Diameters and Covalently Bound Redox-active Modifications,

Nonporous spherical silica nanoparticles resulting from a controlled Stöber process are covalently surface modified with redox-active molecules. Ferrocene, a ruthenium(II) complex with an N2P2Cl2 ligand set, and a sterically hindered biphenylamine are used as modifiers. The resulting materials are characterized by physical, spectroscopic, electrochemical, and chemical methods. The cyclic voltammetric behavior is studied in detail and reveals effects of charge transport by electron hopping along the surface of particles adsorbed on a Pt electrode. The ruthenium(II) complex remains catalytically active with respect to hydrogenation upon immobilization on the particles. Thus, the respective material provides a heterogenized homogeneous hydrogenation catalyst on a solid support.

Synthesis and characterization of nanoporous metallic platinum

Nanoporous metallic platinum with a high specific surface area of 91 m 2/g was synthesized by a templating method using nonporous silica nanoparticles. The templating reaction is constituted of four steps: (1) a coating reaction of a Pt compound on the silica surface; (2) reduction of the Pt compound; (3) dissolution of the silica by alkaline treatment; (4) removal of residual carbon in the nanoporous platinum by heat treatment. Thus, nanoporous metallic platinum, stabilized by a small amount of carbon, can successfully be obtained by a relatively convenient synthetic process. This material can be a promising model material for development of new scientific fields concerned with electromagnetic properties and a functional material applicable to fuel cell or catalytic reactions.

Agglomerated non-porous silica nanoparticles as model carriers in polyethylene synthesis

Non-porous submicron silica particles (250 and 500 nm) with high monodispersity were agglomerated to form spherical agglomerates via spray drying. As a binder, 25 nm sized monodisperse silica spheres were selected from a variety of colloidal systems including Levasil-type and Aerosil-type silica nanoparticles. The use of such binders led to an increase of the specific surface area of the agglomerated carriers. All materials were characterised by nitrogen sorption, mercury intrusion and scanning electron microscopy. The silica agglomerates, with highly defined geometrical and pore structural parameters, were employed as model carriers in the heterogeneous polymerization of ethylene using a conventional methylaluminoxane (MAO)/η5-dicyclopentadienyl zirconiumdichloride metallocene catalyst system. The activity of these model carriers was evaluated, as was the influence of MAO impregnation on the carriers’ physico-chemical properties. The activity of the presented catalyst systems depended heavily on the percentage of binder. Due to skin formation, high contents of binder resulted in agglomerates with a smoother, more rigid surface. These carriers did not fragment during polymerization, and displayed low catalytic activity. Less binder gave more readily fragmented agglomerates displaying higher catalytic activities. Despite their small specific surface areas in comparison to commercially available polymerization carriers, e.g. SYLOPOL 948 from W.R. Grace, these model carriers possess similar activities, with the polymerization process depending more on the geometrical and structural aspects of the beads rather than on their specific surface areas.

Adsorption and excimer formation of 4-(1-pyrenyl)-butyltrimethylammonium bromide on non-porous silica nanoparticles in aqueous dispersions

Adsorption and excimer formation of 4-(1-pyrenyl)-butyltrimethylammonium bromide (PyB) on non-porous silica nanoparticles (Aerosil) have been studied in aqueous dispersions. The efficiency of excimer formation is remarkably enhanced on going from the homogeneous aqueous solution to the silica dispersion. This is ascribed to the effective adsorption of PyB onto the silica surfaces. Adsorption isotherm data are not fitted to a simple Langmuir binding model, suggesting cluster formation of PyB molecules on the silica surfaces. From the dependence of PyB excimer fluorescence intensity on the surface density of the probe on the silica surface, it is elucidated that PyB molecules are inhomogeneously distributed on the surfaces. Excitation spectra and fluorescence decay curves reveal that the excimers of PyB on Aerosil surfaces are mainly originated from ground-state dimers, i.e. dynamic processes through lateral diffusion of the probe on the surface are less important in the present case.