Self-assembled template-directed synthesis of one-dimensional silica and titania nanostructures

Mineralized biological materials such as shells, skeleton, and teeth experience biomineralization. Biomimetic materials exploit the biomineralization process to form functional organic-inorganic hybrid nanostructures. In this work, we mimicked the biomineralization process by the de novo design of an amyloid-like peptide that self-assembles into nanofibers. Chemically active groups enhancing the affinity for metal ions were used to accumulate silicon and titanium precursors on the organic template. The self-assembly process and template effect were characterized by CD, FT-IR, UV-vis, fluorescence, rheology, TGA, SEM, and TEM. The self-assembled organic nanostructures were exploited as a template to form high-aspect-ratio 1-D silica and titania nanostructures by the addition of appropriate precursors. Herein, a new bottom-up approach was demonstrated to form silica and titania nanostructures that can yield wide opportunities to produce high-aspect-ratio inorganic nanostructures with high surface areas. The materials developed in this work have vast potential in the fields of catalysis and electronic materials.     

Synthesis and properties of colloidal heteronanocrystals

Colloidal heteronanocrystals (HNCs) can be regarded as solution-grown inorganic-organic hybrid nanomaterials, since they consist of inorganic nanoparticles that are coated with a layer of organic ligand molecules. The hybrid nature of these nanostructures provides great flexibility in engineering their physical and chemical properties. The inorganic particles are heterostructured, i.e. they comprise two (or more) different materials joined together, what gives them remarkable and unique properties that can be controlled by the composition, size and shape of each component of the HNC. The interaction between the inorganic component and the organic ligand molecules allows the size and shape of the HNCs to be controlled and gives rise to novel properties. Moreover, the organic surfactant layer opens up the possibility of surface chemistry manipulation, making it possible to tailor a number of properties. These features have turned colloidal HNCs into promising materials for a number of applications, spurring a growing interest on the investigation of their preparation and properties. This critical review provides an overview of recent developments in this rapidly expanding field, with emphasis on semiconductor HNCs (e.g., quantum dots and quantum rods). In addition to defining the state of the art and highlighting the key issues in the field, this review addresses the fundamental physical and chemical principles needed to understand the properties and preparation of colloidal HNCs (283 references).     

Surfactants as Promising Media for the Preparation of Crystalline Inorganic Materials

Given that surfactants can control the shape and size of micro‐/nanoparticles, they should be able to direct the growth of bulk crystals. This Minireview summarizes recent developments in the application of surfactants for the preparation of new crystalline inorganic materials, including chalcogenides, metal–organic frameworks, and zeolite analogues. The roles of surfactants in different reaction systems are discussed.     

Hybrid Organic–Inorganic Thermoelectric Materials and Devices

Hybrid organic–inorganic materials have been considered as a new candidate in the field of thermoelectric materials since the last decade owing to their great potential to enhance the thermoelectric performance by utilizing the low thermal conductivity of organic materials and the high Seebeck coefficient, and high electrical conductivity of inorganic materials. Herein, we provide an overview of interfacial engineering in the synthesis of various organic–inorganic thermoelectric hybrid materials, along with the dimensional design for tuning their thermoelectric properties. Interfacial effects are examined in terms of nanostructures, physical properties, and chemical doping between the inorganic and organic components. Several key factors which dictate the thermoelectric efficiency and performance of various electronic devices are also discussed, such as the thermal conductivity, electric transportation, electronic band structures, and band convergence of the hybrid materials.     

Coordination polymer nanofibers generated by microfluidic synthesis

One-dimensional coordination polymer nanostructures are an emerging class of nanoscale materials with many potential applications. Here, we report the first case of coordination polymer nanofibers assembled using microfluidic technologies. Unlike common synthetic procedures, this approach enables parallel synthesis with an unprecedented level of control over the coordination pathway and facilitates the formation of 1D coordination polymer assemblies at the nanometer length scale. Finally, these nanostructures, which are not easily constructed with traditional methods, can be used for various applications, for example as templates to grow and organize functional inorganic nanoparticles.     

Interfacially formed organized planar inorganic, polymeric and composite nanostructures

This paper discusses synthetic strategies for fabrication of new organized planar inorganic, polymeric, composite and bio-inorganic nanostructures by methods based on chemical reactions and physical interactions at the gas-liquid interface, Langmuir monolayer technique, interfacial ligand exchange and substitution reactions, self-assembling and self-organization processes, DNA templating and scaffolding. Stable reproducible planar assemblies of ligand-stabilized molecular nanoclusters containing definite number of atoms have been formed on solid substrate surfaces via preparation and deposition of mixed Langmuir monolayers composed by nanocluster and surfactant molecules. A novel approach to synthesis of inorganic nanoparticles and to formation of self-organized planar inorganic nanostructures has been introduced. In that approach, nanoparticles and nanostructures are fabricated via decomposition of insoluble metal-organic precursor compounds in a layer at the gas-liquid interface. The ultimately thin and anisotropic dynamic monomolecular reaction system was realized in that approach with quasi-two-dimensional growth and organization of nanoparticles and nanostructures in the plain of Langmuir monolayer. Photochemical and redox reactions were used to initiate processes of interfacial nucleation and growth of inorganic phase. It has been demonstrated that morphology of resulting inorganic nanostructures can be controlled efficiently by variations of growth conditions via changes in state and composition of interfacial planar reaction media, and by variations of composition of adjacent bulk phases. Planar arrays and chains of iron oxide and ultrasmall noble metal (Au and Pd) nanoparticles, nanowires and new organized planar disk, ring, net-like, labyrinth and very high-surface area nanostructures were obtained by methods based on that approach. Highly organized monomolecular polymeric films on solid substrates were obtained via deposition of Langmuir monolayer formed by water-insoluble amphiphilic polycation molecules. Corresponding nanoscale-ordered planar polymeric nanocomposite films with incorporated ligand-stabilized molecular metallic nanoclusters and interfacially grown nanoparticles were fabricated successfully. Novel planar DNA complexes with amphiphilic polycation monolayer were formed at the gas-aqueous phase interface and then deposited on solid substrates. Toroidal and new net-like conformations were discovered in those complexes. Nanoscale supramolecular organization of the complexes was dependent on cationic amphiphile monolayer state during the DNA binding. These monolayer and multilayer DNA/amphiphilic polycation complex Langmuir-Blodgett films were used as templates and nanoreactors for generation of inorganic nanostructures via metal cation binding with DNA and following inorganic phase growth reactions. As a result, ultrathin polymeric nanocomposite films with integrated DNA building blocks and organized inorganic semiconductor (CdS) and iron oxide quasi-linear nanostructures were formed. It has been demonstrated that interaction of deposited planar DNA/amphiphilic polycation complexes with bulk phase colloid inorganic cationic ligands (CdSe nano-rods) can result in formation of new highly organized hybrid bio-inorganic nanostructures via interfacial ligand exchange and self-organization processes. The methods developed can be useful for investigation of fundamental mechanisms of nanoscale structural organization and transformation processes in various inorganic and molecular systems including bio-molecular and bio-inorganic nanostructures. Also, those methods are relatively simple, environmentally safe and thus could prove to be efficient practical instruments of molecular nanotechnology with potential of design and cost-effective fabrication of new controlled-morphology organized planar inorganic and composite nanostructured materials. Possible applications of obtained nanostructures and future developments are also discussed.     

无机纳米稀土发光材料的制备方法*

无机纳米稀土发光材料作为一种重要的发光材料,由于具有独特的光、电和化学性质,使其在高性能磁体、发光器件、显示、生物标记、光学成像和光学治疗等方面得到了广泛的应用。稀土发光材料的这些性质与材料的尺寸和形状密切相关,近年来研究者已经利用多种合成方法制备了不同形状的纳米稀土发光材料,包括纳米线、纳米棒、纳米管、纳米纤维和纳米片等。本文综述了无机纳米稀土发光材料的几种常用的制备方法,包括水热/溶剂热法、有机/无机前驱体热分解法和超声辅助合成法等,评述了这些方法的优缺点,并结合课题组在无机纳米稀土发光材料制备方面的工作,对无机纳米稀土发光材料制备方法的发展进行了展望。     

Self-assembled hybrid nanofibers confer a magnetorheological supramolecular hydrogel

Most magnetorheological materials, composed of magnetic microparticles in a liquid, require significant amounts of magnetic particles and a large magnetic field to achieve the desired effects. Here, we report on a new type of magnetorheological materials consisting of small amounts of magnetic nanoparticles (0.8 wt %) but exhibiting large rheological change (i.e., a gel-sol transition) upon the application of a small magnetic field. We use self-assembly to create hybrid nanofibers, which consist of supramolecular hydrogelators and magnetic nanoparticles, as the matrices of the hydrogel. Localized in the nanofibers at a distance of 1-2 nm, the magnetic nanoparticles occupy a small volume fraction of the hydrogel, significantly enhancing the magnetic dipole interactions between them, which results in the large magnetoresponse. This strategy generates a hierarchical nanostructure and eliminates several drawbacks of the simple mixture of polymers with nanoparticles, and thus provides a new methodology that uses magnetic force to control the nanostructures and properties of soft materials.     

Triplex DNA Nanostructures: From Basic Properties to Applications

Triplex nucleic acids have recently attracted interest as part of the rich “toolbox” of structures used to develop DNA‐based nanostructures and materials. This Review addresses the use of DNA triplexes to assemble sensing platforms and molecular switches. Furthermore, the pH‐induced, switchable assembly and dissociation of triplex‐DNA‐bridged nanostructures are presented. Specifically, the aggregation/deaggregation of nanoparticles, the reversible oligomerization of origami tiles and DNA circles, and the use of triplex DNA structures as functional units for the assembly of pH‐responsive systems and materials are described. Examples include semiconductor‐loaded DNA‐stabilized microcapsules, DNA‐functionalized dye‐loaded metal–organic frameworks (MOFs), and the pH‐induced release of the loads. Furthermore, the design of stimuli‐responsive DNA‐based hydrogels undergoing reversible pH‐induced hydrogel‐to‐solution transitions using triplex nucleic acids is introduced, and the use of triplex DNA to assemble shape‐memory hydrogels is discussed. An outlook for possible future applications of triplex nucleic acids is also provided.     

Composite block copolymer stabilized nanoparticles: simultaneous encapsulation of organic actives and inorganic nanostructures

We describe the preparation and characterization of hybrid block copolymer nanoparticles (NPs) for use as multimodal carriers for drugs and imaging agents. Stable, water-soluble, biocompatible poly(ethylene glycol)-block-poly(epsilon-caprolactone) NPs simultaneously co-encapsulating hydrophobic organic actives (beta-carotene) and inorganic imaging nanostructures (Au) are prepared using the flash nanoprecipitation process in a multi-inlet vortex mixer. These composite nanoparticles (CNPs) are produced with tunable sizes between 75 nm and 275 nm, narrow particle size distributions, high encapsulation efficiencies, specified component compositions, and long-term stability. The process is tunable and flexible because it relies on the control of mixing and aggregation timescales. It is anticipated that the technique can be applied to a variety of hydrophobic active compounds, fluorescent dyes, and inorganic nanostructures, yielding CNPs for combined therapy and multimodal imaging applications.     

Optical probes of chain packing structure and exciton dynamics in polythiophene films,composites, and nanostructures

This mini-review on the photophysics of poly-alkyl thiophenes (e.g., P3HT) and its blends with electron-acceptor moeties such as fullerenes (e.g., PCBM) and carbon nanotubes focuses on highlights of recent literature on spectroscopic probes of exciton formation, diffusion, charge-separation, and transport in these materials. The literature in this area is vast: more than 3000 papers have been published in on P3HT (and related materials) and applications to organic solar energy harvesting devices over the last 20 years. Thus, no single review can capture the breadth and depth of this research. Here, we attempt to highlight some of the exciting new research efforts aimed at understanding photophysical processes in organic photovoltaic materials. This mini-review is organized as follows: First, a summary of the theoretical framework commonly used to describe fundamental physical processes of charge generation in organic (polymeric) semiconductor materials is presented. We then discuss recent exciting results on ultrafast spectroscopic probes of exciton dynamics in these materials. Finally, we present highlights of new research on polymer nanostructures (nanoparticles and nanofibers) and their exciting applications to organic photovoltaics. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

气体膨胀液体技术制备纳米微粒研究进展

近年来,利用气体膨胀液体的相行为已经开发了许多气体膨胀液体微粒制备方法,并已在制备无机、有机材料、有机金属固体、医药、电子等方面的微细颗粒方面得到广泛应用。本文介绍了气体膨胀液体制备纳米颗粒的研究和应用进展。     

Synthesis of polyaniline nanofibers by "nanofiber seeding"

Seeding a conventional chemical oxidative polymerization of aniline with even very small amounts of biological, inorganic, or organic nanofibers (usually <1%) dramatically changes the morphology of the resulting doped electronic polymer polyaniline from nonfibrillar (particulate) to almost exclusively nanofibers. The nanoscale morphology of the original seed template is transcribed almost quantitatively to the bulk precipitate. These findings could have immediate impact in the design and development of high-surface area electronic materials.     

Deciphering the evolution of supramolecular nanofibers in solution and solid-state: a combined microscopic and spectroscopic approach

Supramolecular self-assembly of small organic molecules has emerged as a powerful tool to construct well-defined micro- and nanoarchitecture through fine-tuning a range of intermolecular interactions. The size, shape, and optical properties of these nanostructures largely depend on the specific assembly of the molecular building units, temperature and polarity of the medium, and external stimuli. The engineering of supramolecular self-assembled nanostructures with morphology-dependent tunable emission is in high demand due to the promising scope in nanodevices and molecular machines. However, probing the evolution of molecular aggregates from the solution and directing the self-assembly process in a pre-defined fashion are challenging. In the present study, we have deciphered the sequential evolution of supramolecular nanofibers from solution to spherical and oblong-shaped nanoparticles through the variation of solvent polarity, tuning the hydrophobic–hydrophilic interactions. An intriguing case of molecular self-assembly has been elucidated employing a newly designed π-conjugated thiophene derivative (TPAn) through a combination of steady-state absorption, emission measurements, fluorescence correlation spectroscopy (FCS), and electron microscopy. The FCS analysis and microscopy results revealed that the small-sized nanofibers in the dispersion further agglomerated upon solvent evaporation, resulting in a network of nanofibers. Stimuli-responsive reversible interconversion between a network of nanofibers and spherical nanoaggregates was probed both in dispersion and solvent-evaporated state. The evolution of organic nanofibers and a subtle control over the self-assembly process demonstrated in the current investigation provide a general paradigm to correlate the size, shape, and emission properties of fluorescent molecular aggregates in complex heterogeneous media, including a human cell.

Supramolecular nanofiber evolution in solution and solid-state, including stimuli-responsive reversible interconversion among diverse nanoarchitectures, was probed through a combined spectroscopic and microscopic approach.     

Fluorescent Gold Nanoparticles: Synthesis of Composite Materials of Two‐Component Disulfide Gels and Gold Nanoparticles

Pseudoenantiomeric ethynylhelicene oligomers containing a disulfide group formed two‐component gels, which showed different solvent properties from gels without the disulfide group. The disulfide gels reacted with gold nanoparticles, and the resulting organic–inorganic composite materials exhibited fluorescence emission between 600–800 nm, along with emission from the oligomers at 450 nm. The disulfide gels and isolated gold nanoparticles loaded with the oligomers did not show the former emission. The 600–800 nm emission reversibly disappeared upon sol formation with heating, which was accompanied by an enhancement of the emission at 450 nm. The novel emission was also observed in the solid state.     

Self-assembly of anisotropic tethered nanoparticle shape amphiphiles

The varied and exotic shapes of new nanoscale organic and inorganic building blocks provide new opportunities to engineer materials possessing specific functionality and physical properties dictated by the unique packings of these particles. We briefly review some of the current strategies for inducing the self-assembly of these building blocks focusing on one strategy in particular—the attachment of tethers to the building blocks at precise locations to create tethered nanoparticle “shape amphiphiles”. We use computer simulation to demonstrate that the resulting anisotropy imparted to nanocrystals or nanocolloids by the tethers can be used to encode simple design rules into the building blocks that ultimately result in a unique self-assembled structure. We present a general classification scheme for tethered nanoparticles wherein the anisotropy of a shape amphiphile is described by a vector comprised of one or more axes each describing a measure of anisotropy.     

Effects of organic ligands, electrostatic and magnetic interactions in formation of colloidal and interfacial inorganic nanostructures

This paper discusses effects of organic ligands, electrostatic and magnetic interactions involved in morphological control of chemically synthesized inorganic nanostructures including colloid and planar systems. The special attention was concentrated on noble metal (gold and palladium) nanoparticles and nanostructures formed at the gas-liquid interface. The analysis of experimental data showed that electrostatic and ligand-related interactions influence very strongly on the metal nanostructure morphology. The hydrophobicity of ligand, charge and binding affinity to inorganic phase are important factors influencing the morphology of inorganic nanostructures formed in a layer at the gas/liquid interface by the interfacial synthesis method. The important point of this method is the quasi two-dimensional character of reaction area and possibilities to realize ultimately thin and anisotropic dynamic monomolecular reaction system with two-dimensional diffusion and interactions of precursors, intermediates and ligands resulting in planar growth and organization of inorganic nanoparticles and nanostructures in the plain of Langmuir monolayer. The morphology of resulting inorganic nanostructures can be controlled efficiently by variations of growth conditions via changes in state and composition of interfacial planar reaction media with the same precursor, and by variations of composition of adjacent bulk phases. The extreme anisotropy and heterogeneity of two-dimensional interfacial reaction system allows creating conditions when growing inorganic particles floating on the aqueous phase surface interact selectively with hydrophobic water-insoluble ligands in interfacial monolayer or with hydrophilic bulk-phase ligands, or at the same time with ligands of different nature present in monolayer and in aqueous phase. The spatial anisotropy of interfacial reaction system and non-homogeneity of ligand binding to inorganic phase gives possibilities for growth of integrated anisotropic nanostructures with unique morphologies, in particularly those characterized by very high surface/volume ratio, high effective perimeter, and labyrinth-like structure. In a case of magnetic nanoparticles dispersed in colloids specific magnetic dipolar interactions can result in formation of chains, rings and more complex nanoparticulate structures or separated highly anisotropic nanoparticles. Theoretical considerations indicate to the importance of system dimensionality in relation to the energy balance which determines specific features of structure organization in planar charged metallic and magnetic nanostructures. For example, a requirement of Coulomb energy minimum, the possibility of free electron redistribution and strengthened attractive interactions between particles in metallic nanostructures can explain formation of very branchy systems with extremely high "effective perimeter". The obtained experimental and literature data show that system dimensionality, organic ligand nature along with electrostatic and magnetic interactions are most important factors of morphological control of chemically synthesized inorganic nanomaterials. The understanding and appropriate exploitation of these factors can be useful for further developments of efficient nanofabrication techniques based on colloidal and interfacial synthetic methods.     

X-ray microanalysis of human cementum.

An energy dispersive x-ray microanalysis study was performed throughout the total length of cementum on five impacted human teeth. Mineral content of calcium, phosphorous, and magnesium were determined with an electron probe from the cemento-enamel junction to the root apex on the external surface of the cementum. The concentration profiles for calcium, phosphorous, and magnesium were compared by using Ca/P and Mg/Ca atomic percent ratio. Our findings demonstrated that the Ca/P ratio at the cemento-enamel junction showed the highest values (1.8-2.2). However, the area corresponding to the acellular extrinsic fiber cementum (AEFC) usually located on the coronal one-third of the root surface showed a Ca/P media value of 1.65. Nevertheless, on the area representing the fulcrum of the root there is an abrupt change in the Ca/P ratio, which decreases to 1.3. Our results revealed that Mg(2+) distribution throughout the length of human cementum reached its maximum Mg/Ca ratio value of 1.3-1.4 at.% around the fulcrum of the root and an average value of 0.03%. A remarkable finding was that the Mg/Ca ratio pattern distribution showed that in the region where the Ca/P ratio showed a decreasing tendency, the Mg/Ca ratio reached its maximum value, showing a negative correlation. In conclusion, this study has established that clear compositional differences exist between AEFC and cellular mixed stratified cementum varieties and adds new knowledge about Mg(2+) distribution and suggests its provocative role regulating human cementum metabolism.     

Well‐Defined Metal–Organic Framework Hollow Nanocages

Metal–organic frameworks (MOFs) have demonstrated great potentials in a variety of important applications. To enhance the inherent properties and endow materials with multifunctionality, the rational design and synthesis of MOFs with nanoscale porosity and hollow feature is highly desired and remains a great challenge. In this work, the formation of a series of well‐defined MOF (MOF‐5, Fe^II‐MOF‐5, Fe^III‐MOF‐5) hollow nanocages by a facile solvothermal method, without any additional supporting template is reported. A surface‐energy‐driven mechanism may be responsible for the formation of hollow nanocages. The addition of pre‐synthesized poly(vinylpyrrolidone)‐ (PVP) capped noble‐metal nanoparticles into the synthetic system of MOF hollow nanocages yields the yolk–shell noble metal@MOF nanostructures. The present strategy to fabricate hollow and yolk–shell nanostructures is expected to open up exciting opportunities for developing a novel class of inorganic–organic hybrid functional nanomaterials.     

PEGylated inorganic nanoparticles

Application of inorganic nanoparticles in diagnosis and therapy has become a critical component in the targeted treatment of diseases. The surface modification of inorganic oxides is important for providing diversity in size, shape, solubility, long-term stability, and attachment of selective functional groups. This Minireview describes the role of polyethylene glycol (PEG) in the surface modification of oxides and focuses on their biomedical applications. Such a PEGylation of surfaces provides "stealth" characteristics to nanomaterials otherwise identified as foreign materials by human body. The role of PEG as structure-directing agent in synthesis of oxides is also presented.