Layered paving of vesicular nanoparticles formed with cerasome as a bioinspired organic-inorganic hybrid

A three-dimensional packed vesicular assembly was successfully prepared by using an organic-inorganic hybrid, the Cerasome. This assembly was achieved by using an alternate layer-by-layer adsorption technique with the anionic and the cationic Cerasome derived from corresponding organoalkoxysilane amphiphiles. Adsorption quantities of each Cerasome layer were evaluated by employing a quartz crystal microbalance. The surface structure of the Cerasome paving on a substrate obtained in this way was observed by atomic force microscopy. The Cerasome particles closely packed like a stone pavement were clearly observed in both layers. In addition, the difference in the particle size for each layer indicates the cationic and anionic Cerasomes undoubtedly formed the layer-by-layer assembly. The layered paving of the vesicular nanoparticles was seen in every layer at least up to ten adsorption steps.     

Cerasome as an Organic-Inorganic Vesicular Nanohybrid: Characterization of Cerasome-Forming Lipids having a Single or a Dual Trialkoxysilyl Head

Morphological characterization of the organic-inorganic vesicular nanohybrids, Cerasomes, was performed in aqueous media from two aspects. Firstly, a novel Cerasome-forming lipid having two triethoxysilyl groups in the head moiety was synthesized and the physical property of the Cerasome was investigated. While the morphological stability of the Cerasomes, as evaluated from the vesicular collapse behavior against a micelle-forming nonionic surfactant, Triton-X 100, was extremely higher than that of the conventional phospholipid liposome, the stabilities were comparable to each other for the Cerasomes derived from the dual- and single-head lipids. On the other hand, the surface property of the Cerasome formed with the dual-head lipid more closely resembled the colloidal silica particles rather than that derived from the single-head lipid, as suggested by zeta-potential measurements. Secondly, the effect of the media pH on the morphological stability of the Cerasome formed with the single-head lipid was evaluated and appeared as a time difference in obtaining the morphological stability of the Cerasome. These morphological characteristics of the Cerasomes could be mainly owing to the development of the siloxane network on the vesicular surface.     

Preparation and Surface Modification of Novel Vesicular Nano-Particle “Cerasome” with Liposomal Bilayer and Silicate Surface

A novel class of nano-hybrid materials, Cerasome, bearing a liposomal bilayer structure and a ceramic surface, has been developed by a sol-gel reaction of a double-chain proamphiphile having an trialkoxysilane in the head moiety and followed self-assembling. In the present work, we developed new methods for preparation of the Cerasomes forming under various pH conditions and their surface modification by employing appropriate alkoxysilane compounds. When the proamphiphilic alkoxysilane was hydrolyzed in an acidic ethanol and then injected into an aqueous media at various pH, the morphologically stable Cerasomes were obtained in a wide pH range. On the other hand, an acid treatment of the proamphiphile in ethanol in the presence of tetraethoxysilane gave the Cerasome with highly developed siloxane networks on its vesicular surface. Surface modification of the Cerasome with amino groups was readily achieved in the similar manner by replacing tetraethoxysilane to 3-aminopropyltriethoxysilane. The Cerasomes thus prepared were characterized by means of dynamic light scattering and zeta potential measurements.     

Silica-supported biomimetic membranes

The hybridization of lipid membranes with inorganic silica-based framework results in mechanically stable biomembrane mimics. This account describes three types of silica-based biomimetic membranes. As the first example, a Langmuir monolayer of dialkylalkoxysilane was polymerized and immobilized onto a porous glass plate. Permeability through the monolayer-immobilized glass was regulated by phase transition of the immobilized monolayer. In the second example, spherical vesicles covalently attached to a silica cover layer (Cerasome) were prepared. The Cerasome was stable enough to be assembled into layer-by-layer films without destruction of its vesicular structure. This material could be an example of the multicellular assembly. Mesoporous silica films densely filling peptide assemblies (Proteosilica) are introduced as the third example. The Proteosilica was synthesized as a transparent film through template sol-gel reaction using amphiphilic peptides.     

Adsorption of polyelectrolyte modified graphene to silica surfaces: monolayers and multilayers

Exfoliated graphene particles stabilised by the cationic polyelectrolyte polyethyleneimine (PEI) were used in conjunction with an anionic polyelectrolyte, poly(acrylic acid), to construct multilayers using the layer-by-layer technique on a silica substrate. In the first adsorption step, the surface excess of the cationic graphene was dependent on the overall charge on the nanoparticle which in turn can be tuned through modifying solution pH as PEI has weakly ionisable charged amine groups. The adsorbed amount onto the silica surface increased as the solution pH increased. Subsequently, a layer of PAA was adsorbed on top of the cationic graphene through electrostatic interaction. The multilayer could be assembled through this alternate deposition, with the influence of solution conditions investigated. The pH of the adsorbing solutions was the chief determinant of the overall adsorbed amounts, with more mass added at the elevated pH of 9 in comparison with pH 4. Atomic force microscopy confirmed that the graphene particles were adsorbed to the silica interface and that the surface coverage of the disc-like nanoparticles was complete after the deposition of five graphene-polyelectrolyte bi-layers. Furthermore, the graphene nanoparticles themselves could be modified through the consecutive addition of the oppositely charged polymers. A multilayered assembly of negatively charged graphene sheets modified with a bi-layer of PEI and PAA was also deposited on a silica surface with adsorbed PEI.     

Incorporation of lipid domains in Cerasome, a morphologically-stable organic-inorganic vesicular nanohybrid

To extend the concept of the Cerasome, an organic-inorganic vesicular nanohybrid, this paper investigates the preparation and characterization of a “mixed” Cerasome. The system consists of a Cerasome-forming lipid 1, a cationic synthetic lipid 2, and a zwitterionic phospholipid 3. Lipid mixtures of 1 and 2 or 1 and 3 were used to prepare the mixed Cerasomes. Their lipid distributions were examined using differential scanning calorimetry (DSC), which showed that 1 and 2 (or 1 and 3) were phase-separated in the mixed Cerasomes. These results seem to be mainly attributable to the polymerizable nature of 1. Results of scanning electron microscopy (SEM) and energy-dispersive X-ray analysis (EDX) showed that 1 and 3 were both incorporated into a single Cerasome, not macroscopically separated to form separate vesicles from each lipid component. Mixed Cerasomes of 1 and 2 showed high morphological stability against a membrane-solubilizing surfactant, incorporating up to 70% of 2. On the other hand, the mixed Cerasomes from 1 and 3 were less stable than the mixed Cerasomes from 1 and 2. This relative instability might be attributable to differences between the mixed Cerasomes from 1 and 2 and 1 and 3 in terms of their vesicular sizes, lipid domain sizes, and their relative effectiveness for siloxane network formation. These results strongly support the formation of mixed Cerasomes that have lipid domains in-plane. Systems described in this study are useful to prepare variously mixed Cerasomes that have different surface functionalities and in-plane lipid distribution, but which have high morphological stability.     

Direct visualization of layer-by-layer self-assembled multilayers of organometallic polymers

Direct visualization of organometallic-organic and novel all-organometallic multilayer superlattices prepared by layer-by-layer assembly of cationic/anionic polyferrocenylsilane and anionic polystyrene sulfonate polyelectrolytes using a gold coating/transmission electron microscopy (TEM) technique is reported.     

Close-packed colloidal crystalline arrays composed of silica spheres coated with titania

Titania coated monodisperse silica spheres have been synthesized and fabricated as a close-packed colloidal crystalline array. We have demonstrated that the coated colloidal sphere can be used to control the peak position of the optical stop band through variation of the coating thickness. The titania coated silica spheres were prepared by the layer-by-layer assembly coating process, which reciprocally laminates the cationic polyelectrolyte and the anionic titania nanosheets on a monodisperse silica spheres, and were sintered to change the titania nanosheets to anatase. The Bragg diffraction peak of the colloidal crystalline array shifted to the long wavelength region with an increase of thickness of the titania layer. Angle-resolved reflection spectra measurements clarified that the red shift was caused by increasing of the refractive index with increase of the thickness of the layer. The current work suggests new possibilities for the creation of advanced colloidal crystalline arrays with tunable optical properties from tailored colloidal spheres.     

Formation and structure of polyelectrolyte and nanoparticle multilayers: effect of particle characteristics

The formation and structure of multilayer films containing a cationic polyelectrolyte and anionic silica nanoparticles were studied by means of ellipsometry and atomic force microscopy. Three types of silica particles of different sizes were examined. The density and thickness of the films as well as the adsorption kinetics appear to be strongly dependent on the choice of particle; smaller particles favor the formation of smooth and dense films with a higher content of the inorganic component.     

Conjugated polyelectrolyte-grafted silica microspheres

A direct method for preparation of conjugated polymer-grafted silica particles is reported. Silica particles (0.3 and 5 mum diameter) are treated with a 3-(trimethoxysilyl)propylamine derivative that is functionalized with an aryl iodide unit. A solution step-growth polymerization reaction is performed in solution that contains a dispersion of the aryl iodide-functionalized particles. The reaction is a Pd(0)-catalyzed (Sonogashira) A-B-type polymerization of an oligo(ethylene glycol)-fuctionalized diiodobenzene and a bis(propyloxy)sulfonate-substituted diethynylbenzene. The overall process affords silica particles that feature a surface graft layer of an anionic poly(phenylene ethynylene)-type conjugated polyelectrolyte. The particle surface modification process was monitored by infrared (FTIR) spectroscopy, and the polymer-grafted silica particles were characterized by thermogravimetric analysis, scanning and transmission electron microscopy, confocal fluorescence microscopy, and absorption and fluorescence spectroscopy. The conjugated polyelectrolyte-grafted silica particles are highly fluorescent, and a Stern-Volmer quenching study of the particles' fluorescence with electron-transfer- and energy-transfer-type quenchers shows that the quenching response depends on the type of quenching mechanism.     

Synthesis and Characterization of CdTe@CdS Quantum Dots Layered on Silica Nanoparticles

CdTe@CdS quantum dots, cationic polyelectrolyte poly-diallyldimethylammonium chloride, and anionic polyelectrolyte polyacrylic acid were assembled on the surface of silica nanoparticles based on the electrostatic layer-by-layer self-assembly to prepare fluorescent composite nanoparticles. Transmission electron microscopy showed that the particles had a uniform size distribution (approximately 70 nm) and good monodispersity. The fluorescence shielding effect of the silica shell was reduced and the assembled quantum dots were well protected by the sandwich structure. The nanoparticles provided strong fluorescence, high stability for storage, and low photobleaching and leakage. Furthermore, they possessed high fluorescence stability and high-concentration staining for cytoplasm, which enabled them to be used for sensitive cellular imaging analysis. Because of the presence of numerous carboxyl groups, they have potential application for biolabeling and bioanalysis.     

Multilayered shell SERS nanotags with a highly uniform single-particle Raman readout for ultrasensitive immunoassays

Novel SERS nanotags with highly uniform and reproducible signals have been developed by the layer-by-layer assembly and crosslinkage of small silver nanoparticles at the surface of silica particles, which opens an avenue to the quantitative and reliable SERS application in bioassays.     

Facile method to fabricate raspberry-like particulate films for superhydrophobic surfaces

A facile method using layer-by-layer assembly of silica particles is proposed to prepare raspberry-like particulate films for the fabrication of superhydrophobic surfaces. Silica particles 0.5 microm in diameter were used to prepare a surface with a microscale roughness. Nanosized silica particles were then assembled on the particulate film to construct a finer structure on top of the coarse one. After surface modification with dodecyltrichlorosilane, the advancing and receding contact angles of water on the dual-sized structured surface were 169 and 165 degrees , respectively. The scale ratio of the micro/nano surface structure and the regularity of the particulate films on the superhydrophobic surface performance are discussed.     

Two-dimensional ordered arrays of aligned lipid tubules on substrates with microfluidic networks

Microfluidic networks is a powerful tool for aligning one-dimensional materials over a large area on solid substrates. Here we show that lipid nano- and microtubules can be assembled into two-dimensional (2-D) parallel arrays with controlled separations by combining fluidic alignment with dewetting, which occurs within microchannels. We also demonstrate that lipid tubules can be bent into a well-defined shape at the entrance of the channels by the capillary force. Atomic force microscopy is used to study the structure and stability of the aligned lipid tubules on substrates. The deposition experiments with silica colloidal particles show that the 2-D parallel-aligned tubules can be used as a template to synthesize silica films with controlled morphologies and patterns on substrates in a single-step process.     

Adsorption of anionic and cationic surfactants on anionic colloids: supercharging and destabilization

We present herein a study on the adsorption of anionic (SDS), cationic (CTAB), and nonionic (C(12)E(5)) surfactants onto anionic silica nanoparticles. The effects of this adsorption are studied by means of the static structure factor, S(q), and the collective diffusion coefficient, D(c), obtained from small-angle X-ray scattering and dynamic light scattering measurements, respectively. The effective charge on the particles was determined also from classical electrophoresis and electroacoustic sonic-amplitude measurements. The surface tension of the sample was also investigated. Of particular note is the adsorption of SDS onto the silica nanoparticles, which leads to supercharging of the interface. This has interesting repercussions for structures obtained by the layer-by-layer (LbL) technique, because emulsions stabilized with supercharged and hydrophobized silica are perfect candidates for use in a multilayer system.     

阴、阳离子表面活性剂混合体系在硅胶/水及硅胶/矿化水界面上的吸附

研究阴、阳离子表面活性剂混合体系(十二烷基氯代吡啶,辛基磺酸钠,辛基三乙基溴化铵/十二烷基苯磺酸钠)在硅胶,纯水和硅胶,矿化水界面上的吸附作用,探讨阴(阳)离子表面活性剂的存在对阳(阴)离子表面活性剂吸附作用的影响．结果表明,阴离子表面活性剂的存在基本不影响阳离子表面活性剂在带负电固体表面的吸附;而阳离子表面活性剂的存在却使本来吸附量就不大的阴离子表面活性剂在带负电的固体表面上不再吸附．在矿化水中阳离子表面活性剂的吸附量比在纯水中明显降低．从硅胶表面吸附机制解释了所得结果．     

Layer-by-layer electrostatic self-assembly of anionic and cationic carbon nanotubes

<正>The layer-by-layer(LBL) self assembly of anionic and cationic multi-walled carbon nanotubes(MWNTs) through electrostatic interaction has been carried out to fabricate all-MWNT multilayer films.The alternate uniform assembly of anionic and cationic MWNTs was investigated by UV-vis spectroscopy.Scanning electron microscopy(SEM) images displayed the growth of the MWNT films.     

Nanoengineered polymeric S-layers based capsules with targeting activity

Nanostructured polymeric capsules are regarded as highly promising systems with different potential applications ranging from drug delivery, biosensing and artificial cells. To fully exploit this potential, it is required to produce bio-activated stable and biocompatible capsules. To this purpose, in present work we proposed the combination of the layer-by-layer self assembly method with bacterial S-layer technology to fabricate stable and biocompatible polymeric capsules having a well defined arrangement of functional groups allowing the covalent attachment of antibody molecules. Hollow microcapsules were obtained by the layer-by-layer self assembly of oppositely charged polyelectrolytes onto colloidal particles, followed by removal of the cores at acidic pH. S-layers were crystallized onto the shell of the obtained capsules. Quartz crystal microbalance was used to characterize the crystallization process onto planar surfaces. S-layer containing capsules were investigated by atomic force microscopy. Immunoenzymatic tests were performed to assess the effective modification of the S-layer with antibody molecules both on planar surfaces and on hollow capsules. Fluorescent microscopy was employed to visualize the presence of the antibody molecules onto the capsule shell and immunological tests used to assess the bioactivity of the immobilized antibodies. Finally, the in vitro cytotoxicity of fabricated S-layer containing capsules was studied. The obtained results demonstrated the possibility to fabricate bio-activated S-layer containing capsules with improved features in terms of biocompatibility.     

Effect of Hydrodynamic Forces on meso‐(4‐Sulfonatophenyl)‐Substituted Porphyrin J‐Aggregate Nanoparticles: Elasticity,Plasticity and Breaking

The J aggregates of 4‐sulfonatophenyl meso‐substituted porphyrins are non‐covalent polymers obtained by self‐assembly that form nanoparticles of different morphologies. In the case of high aspect‐ratio nanoparticles (bilayered ribbons and monolayered nanotubes), shear hydrodynamic forces may modify their shape and size, as observed by peak force microscopy, transmission electron microscopy of frozen solutions, small‐angle X‐ray scattering measurements in a disk‐plate rotational cell, and cone–plate rotational viscometry. These nanoparticles either show elastic or plastic behaviour: there is plasticity in the ribbons obtained upon nanotube collapse on solid/air interfaces and in viscous concentrated nanotube solutions, whereas elasticity occurs in the case of dilute nanotube solutions. Sonication and strong shear hydrodynamic forces lead to the breaking of the monolayered nanotubes into small particles, which then associate into large colloidal particles.     

Driving forces for layer-by-layer self-assembly of films of SiO2 nanoparticles and heme proteins

Heme protein hemoglobin (Hb) or myoglobin (Mb) and silica nanoparticles in a variety of charge states were assembled layer-by-layer into films on solid surfaces to investigate the driving forces for film assembly. Cyclic voltammetry (CV), quartz crystal microbalance (QCM), X-ray photoelectron spectroscopy (XPS), and UV-vis and reflectance absorption infrared (RAIR) spectroscopy were used to characterize the different [SiO2/protein]n films. Even when the proteins and silica were both negatively charged, stable layer-by-layer [SiO2/protein]n films were successfully fabricated, although amounts of protein were smaller than when nanoparticles and proteins had opposite charges. Results suggest the importance of localized Coulombic attractions between the negative nanoparticle surface and positively charged amino acid residues on the Mb or Hb surfaces in the assembly and for the stability of [SiO2/protein]n films.