Formation of orientation-ordered superlattices of magnetite magnetic nanocrystals from shape-segregated self-assemblies

Magnetic magnetite (Fe3O4) nanocrystals have been synthesized by combining nonhydrolytic reaction with seed-mediated growth. The shape of these magnetite nanocrystals can be controlled either as pure spheres or a mixture of mainly faceted nanocrystals. Faceted magnetite nanocrystals consist of truncated tetrahedral platelets (TTPs), truncated octahedrons (TOs), and octahedrons (OTs). Transmission electron microscopy analysis indicates that the faceted nanocrystal mixture tends to self-segregate based upon the shape in a self-assembly process, and each shape forms its own distinct crystallographic orientation-ordered superlattice assemblies. Self-assemblies of the Fe3O4 nanocrystals in the shapes of TTP, TO, and OT show hexagonal, primitive cubic, and distorted body-centered cubic (bcc) superlattice structures, respectively. The possible mechanism for the formation of different superstructures is attributed to van der Waals interactions. Nanocrystals with different shapes provide diverse building blocks for bottom-up approaches in building nano- and mesosystems. Furthermore, the self-segregation phenomenon of different shaped nanocrystals in self-assembly processes could be very important in envisioning efficient assembly strategies for nanoscience- and nanotechnology-based devices.     

Self-assembly of gold nanorods into symmetric superlattices directed by OH-terminated hexa(ethylene glycol) alkanethiol

The self-assembly of anisotropic gold nanorods (GNRs) into ordered phases remains a challenge. Herein, we demonstrated the fabrication of symmetric circular- or semicircular-like self-assembled superlattices composed of multilayers of standing GNRs by fine-tuning the repulsive interactions among GNRs. The repulsive force is tailored from electrostatic interaction to steric force by replacing the surface coating of cetyltrimethylammonium bromide (CTAB) (ζ potential of 20-50 mV) with an OH-terminated hexa(ethylene glycol) alkanethiol (here termed as EG(6)OH, ζ potential of -10 mV). The assembly mechanism is discussed via theoretical analyses of the major interactions, and an effective balance between the repulsive steric and attractive depletion interactions is the main driving force for the self-assembly. The real-time observations of solution assembly (UV-vis-NIR absorption spectroscopy) supports the mechanism that we suggested. The superlattices obtained here not only enrich the categories of the self-assembled structures but more importantly deepen the insight of the self-assembly process and pave the way for various potential applications.     

环糊精与表面活性剂主客体作用诱导的金纳米棒可控自组装

The self-assembly of colloidal nanocrystals has emerged as a powerful strategy for the bottom-up fabrication of functional materials and nanodevices. Recently, the self-assembly of gold nanorods (GNRs) has attracted significant attention because of their unique plasmonic properties, but the realization of their adjustable self-assembly of GNRs through facile and effective approaches remains challenging. In this work, the controllable self-assembly of GNRs in aqueous solution was realized through the host-guest interactions of cyclodextrins (CDs) and the cetyltrimethylammonium bromide (CTAB) molecules adsorbed on the surface of the GNRs. The self-assembly of GNRs was readily achieved by the addition of aqueous α-CD solutions with varied concentrations into aqueous dispersions of CTAB-stabilized GNRs. At a relatively low α-CD concentration, slow aggregation of the GNRs occurred, resulting in their side-by-side assembly. This was revealed by the blue shift of the longitudinal surface plasmon resonance (LSPR) band in the absorption spectra and confirmed by transmission electron microscopy (TEM) observations. On the other hand, when a higher concentration of α-CD was added, fast aggregation of the GNRs occurred, resulting in their end-to-end assembly. This was revealed by the red shift in the LSPR band together with the TEM observations. If β-CD was employed instead of α-CD, the self-assembly of GNRs could also be induced, although a relatively higher concentration of β-CD was required to achieve the extent of aggregation similar to that induced by α-CD, indicating that the supramolecular host–guest interaction between CDs and the surfactant CTAB was crucial to the directed self-assembly of GNRs. Furthermore, the α-CD-induced assembly was inhibited on addition of excess CTAB, confirming that the supramolecular interaction of α-CD and CTAB played a key role in directing the self-assembly of the GNRs. Based on these experimental results, a possible mechanism for the α-CD-induced self-assembly of GNRs was proposed as follows: at a lower α-CD concentration, the gradual formation of the host-guest inclusion complex α-CD/CTAB led to the partial replacement of the highly charged CTAB bilayers adsorbed on the GNRs by the less charged complex, which resulted in a slow side-by-side assembly of the GNRs; at a higher α-CD concentration, the CTAB bilayers were quickly replaced by the α-CD/CTAB complex, and the CTAB molecules adsorbed at both ends of the GNRs were almost completely replaced, resulting in a fast end-to-end assembly of the GNRs. Additionally, on the basis of the hydrolysis of α-cyclodextrin catalyzed by α-amylase, the self-assembly of GNRs directed by the host-guest interaction could be used to realize the feasible detection of α-amylase in solutions. This self-assembly strategy mediated by the host-guest interaction may be extendable to other colloidal systems involving surfactants adsorbed on the surface of nanoparticles, and may open new avenues for the controllable self-assembly of non-spherical nanoparticles.     

Nanocrystals modified with peptide nucleic acids (PNAs) for selective self-assembly and DNA detection

Gold nanocrystals modified with peptide nucleic acids (PNAs) have been prepared and applied to self-assembly and DNA sensing. Experiments with different PNA structural motifs show that (1). the versatility in PNA synthetic design can be used to modulate the electrostatic surface properties of nanocrystals, presenting an opportunity to control assembly rate and aggregate size, (2). short (6 base) PNAs can hybridize effectively while attached to nanoparticles, providing a route to generating materials with small interparticle spacings, and (3). the superior base pair mismatch selectivity of PNAs is further enhanced on nanosurfaces, enabling PNA-modified nanoparticles to act as highly selective nanoscale sensors, as well as synthons for defect-free self-assembly. This last feature was coupled with a substantial change in colloidal stability upon DNA hybridization to develop a novel colorimetric DNA assay that detects the presence of single base imperfections within minutes. Various modes of PNA hybridization, including the first practical application of PNA-PNA interactions, were used to direct the assembly of nanoparticles into macroscopic arrangements. Shorter duplex interconnects and greater specificity in assembly were obtained compared to similar experiments with DNA-modified nanocrystals.     

Shape tunable synthesis of anisotropic gold nanostructures through binary surfactant mixtures

In recent years, much effort has been made to produce gold (Au) nanorods of different sizes through the use of binary surfactant mixtures via a seed-mediated growth approach. However, how the ratio of two different surfactants influences the shape of the resulting Au nanoparticles remains to be elucidated. Here, we report the shape-controlled synthesis of Au nanoparticles using a binary surfactant mixture of CTAB (cetyltrimethylammonium bromide) and DDAB (didodecyldimethylammonium bromide) via a silver-assisted seed-mediated growth approach. Decreasing the CTAB/DDAB ratio results in a shape transition from Au nanorods to elongated tetrahexahedra and finally to Au bipyramids. The results showed significant improvement in the yield of Au bipyramidal type nanoparticles in different sizes (nm to μm) by using binary surfactant mixtures without any need for shape selection procedure. By varying the pH and concentration of ascorbic acid, we can control the shape and size of Au nanoparticles (i.e., truncated bipyramids, dogbones, and nanodumbbells) at fixed CTAB/DDAB ratios. A preliminary growth mechanism has been proposed based on the change in the mixed micelle soft-template induced by the increasing concentration of DDAB and reaction parameters (i.e., pH, concentration of ascorbic acid). These results constitute the advances in the understanding for synthesizing anisotropic Au nanoparticles of tunable optical properties via engineering the design of a soft-template. These anisotropic Au nanoparticles, especially, bipyramids of different morphologies and sizes are potential candidates for the enhancement of the optical response and developing label-free biosensing devices.     

Fractal metal nanoparticle aggregates morphology formation mediated by polyelectrolyte/surfactant complex films at interfaces

In this work, the gold nanoparticle self-assembly behavior of mica-surface-confined polyelectrolyte/surfactant complex films was investigated. First, modified partially hydrated polyacrylamide (MHPAM)/hexadecyltrimethylammonium bromide (CTAB) complex films were deposited on the mica surface using Langmuir–Blodgett technique. Then, the preadsorbed MHPAM/CTAB complex film mica plate was dipped into the gold aqueous solution and the interesting fractal nanostructured gold network was formed. In addition, the effect of dipping time on gold nanoparticle self-assembly morphology was studied. The mechanism of formation process is briefly proposed.     

Synthesis of Barium Lithium Fluoride Nanocrystals Using Reverse Micelles as Microemulsion

Barium lithium fluoride nanocrystals were synthesized in cetyltrimethylammonium bromide (CTAB)/2-octanol/water microemulsion systems. The impurity peaks in XRD patterns were not determined. The result of SEM confirmed that the average sizes and shape of the BaLiF3 nanocrystals. The formation of BaLiF3 and particles size were strongly affected by water content. With increasing water content and reaction times, the size of the particle increases.Meanwhile, the solvent was also found to play a key role in the synthesis of the BaLiF3 nanocrystals.     

Self-assembled NiO-ZrO2 nanocrystals with mesoscopic void space: an efficient and green catalyst for C-S cross-coupling reaction in water

New NiO-ZrO(2) nanocrystals (MNZ-1) with mesoscopic self-assembly have been synthesized by using a non-ionic surfactant as the structure directing agent (SDA) via evaporation induced self-assembly (EISA) method. Powder X-ray diffraction (PXRD), N(2) sorption study and transmission electron microscopic (TEM) image analyses revealed the cubic structure, mesoporosity and mesoscopic self-assembly of ca. 7.0 nm sized tiny nanocrystals in the material. MNZ-1 catalyzes the aerobic aryl-sulfur cross-coupling reactions for a series of aryl-iodides with 4-chlorothiophenol in environment friendly water medium at elevated as well as room temperature. Pure ZrO(2) mesoporous nanocrystals are inactive, whereas pure NiO nanocrystals showed much lower catalytic activity under similar reaction conditions. The MNZ-1 nanocatalyst is completely non-air sensitive, inexpensive and effective for the synthesis of a series of essential biomolecules derived from diaryl sulfides.     

球状、立方状及空心立方状PbS纳米晶的控制合成及其形成机理

以醋酸铅为铅源,硫代乙酰胺为硫源,在表面活性剂十二烷基硫酸钠(SDS)和十六烷基三甲基溴化铵(CTAB)共同作用下,通过简单地调节水热反应的反应温度控制合成出球状、立方状和空心立方状PbS纳米晶。利用XRD、TEM对合成产物的结构和形貌进行了表征,发现合成的球状、立方状和空心立方状PbS纳米晶尺寸均一,直径为100 nm左右。对球状、立方状和空心立方状PbS纳米晶的形成机理进行了初探,结果表明反应温度较低时,水热反应初始阶段形成的PbS小颗粒呈球形,在表面活性剂SDS的烷基链模板和CTAB微胶束软模板共同作用下生成球状PbS纳米晶;反应温度较高时,水热反应初始阶段形成的PbS小颗粒由于自身的立方相岩盐晶体结构的影响有呈立方状趋势,在SDS和CTAB共同作用下产物堆积成空心立方体状或立方状。     

Direct synthesis of branched gold nanocrystals and their transformation into spherical nanoparticles

We report a facile synthesis of branched gold nanocrystals by the addition of a suitable amount of NaOH to an aqueous solution of cetyltrimethylammonium bromide (CTAB), HAuCl(4), and ascorbic acid. The branched nanocrystals were formed within minutes of reaction and showed monopod, bipod, tripod, and tetrapod structures. They are crystalline and have smooth surfaces. These gold multipods are kinetically controlled products and are thermodynamically unstable. The branched nanocrystals quickly transformed into spherical nanoparticles within 1 h of reaction, and the process was essentially complete after 2 days. The morphological transformation has been monitored by both UV-vis absorption spectroscopy and electron microscopy. The appearance of two major absorption bands for the branched gold nanocrystals eventually became only a single band at 529 nm for the spherical nanoparticles. The resulting nanoparticles are single crystals with diameters of 20-50 nm and do not show a faceted structure. When the freshly prepared branched nanocrystals are kept in a refrigerator at 4 degrees C, their multipod structure can be preserved for over a month without significant spectral shifts.     

Synthesis and self-assembly of highly monodispersed quasispherical gold nanoparticles

We report the synthesis of cetyltrimethylammonium bromide (CTAB) assisted seed mediated growth of highly pure and monodispersed quasispherical gold nanoparticles (QAuNPs) and their self-assembly on the silica/glass substrates. The seed-mediated growth approach was modified to prepare size-tunable monodispersed QAuNPs with sizes ranging from 20 to 150 nm. The larger, more uniform seeds and lower CTAB concentration resulted in the formation of relatively large QAuNPs with improved monodispersity (relative standard deviation (RSD) of ～5-8%) and high purity in their shapes. In addition, CATB-capped QAuNPs can be spontaneously assembled into closely packed and highly aligned superstructures with well-defined mutillayers (two to six layers) on silica substrates. Furthermore, CATB-capped QAuNPs can easily construct density-controllable QAuNP chips by electrostatic self-assembly, showing their promising applications for single-nanoparticle plasmonic sensors.     

氧化铜纳米晶的合成及性能研究

通过水热方法,合成出CuO纳米片,类纳米花等纳米结构,X光衍射表明样品为单斜CuO,透射电镜和高分辨透射电镜表征了样品的形貌和尺寸,观察到CuO纳米晶是由小的晶粒聚集而成的多晶结构。同时讨论了实验中各实验参数在合成CuO纳米晶时所起的作用： KOH具有促进CuO结晶的作用;十六烷基三甲基溴化铵可以控制反应产物尺寸;柠檬酸钠能够影响纳米粒子的排布规则程度,从而进一步影响CuO纳米晶的形貌和尺寸。另外我们还研究了CuO纳米片的光学性能和氮气吸附性质。     

Reinforcement of hydroxypropylcellulose films by cellulose nanocrystals in the presence of surfactants

Hydroxypropylcellulose (HPC) films were prepared by casting with cellulose nanocrystals in the presence of anionic surfactant sodium dodecylsulphate (SDS) and cationic surfactant hexadecyltrimethyl ammonium bromide (CTAB). The cellulose nanocrystals were isolated from maize straw, a biomass source produced in huge quantities as an agrowaste in Brazil. These bionanocomposite films had good transparency and their surface hydrophilic character was evidenced by static contact angle measurements. Thermogravimetry (TGA) measurement revealed that nanocrystals and surfactants changed the thermal stability of the HPC films. Dynamic mechanical analysis (DMA) showed that the tensile storage and loss moduli of the HPC films increased by increasing the contents of cellulose nanocrystals and surfactants, especially in the case of CTAB. This good reinforcing effect of HPC matrix can be explained as due to electrostatic attractive interactions brought about by the presence of CTAB and the nanocrystals.     

Chemically Modified Electrodes for Recessed Microelectrode Array

Chemical modifications on recessed microelectrode array, achieved via electrodeposition techniques are reported here. Silicon-based gold microelectrode arrays of 10 μm microband and microdisc array were selected and functionalised using sol-gel and nanoporous gold (NPG) respectively. For electrochemically assisted self-assembly (EASA) formati6154on of sol-gel, electrode surface was first pre-treated with a self-assembled partial monolayer of mercaptopropyltrimethoxysilane (MPTMS) before transferring it into the sol containing cetyltrimethyl ammonium bromide (CTAB)/tetraethoxysilane (TEOS):MPTMS (90:10) precursors. A cathodic potential is then applied. It was found that larger current densities were required in ensuring successful film deposition when moving from macro- to micro- dimensions. For NPG modification, a chemical etching process called dealloying was employed. NPG of three different thicknesses have been successfully deposited. All the modified and functionalized microelectrode arrays were characterized by both optical (SEM) and electrochemical analysis (cyclic voltammetry and impedance spectroscopy). An increase in surface area and roughness has been observed and such will benefit for future sensing application.     

Plasmonic vesicles of amphiphilic gold nanocrystals: self-assembly and external-stimuli-triggered destruction

We have developed a new class of plasmonic vesicular nanostructures assembled from amphiphilic gold nanocrystals with mixed polymer brush coatings. One major finding is that the integration of gold nanocrystals (nanoparticles and nanorods) with two types of chemically distinct polymer grafts, which are analogous to block copolymers as a whole, creates a new type of hybrid building block inheriting the amphiphilicity-driven self-assembly of block copolymers to form vesicular structures and the plasmonic properties of the nanocrystals. In contrast to other vesicular structures, the disruption of the plasmonic vesicles can be triggered by stimulus mechanisms inherent to either the polymer or the nanocrystal. Recent advances in nanocrystal synthesis and controlled surface-initiated polymerization have opened a wealth of possibilities for expanding this concept to other types of nanocrystals and integrating different types of nanocrystals into multifunctional vesicles. The development of multifunctional vesicles containing stimuli-responsive polymers could enable their broader applications in biosensing, multimodality imaging, and theragnostic nanomedicine.     

Heterochiral Self-Discrimination-Driven Supramolecular Self-Assembly of Decanuclear Gold(I)-Sulfido Complexes into 2D Nanostructures with Chiral Anions-Tuned Morphologies

Chiral self-recognition and self-discrimination are of vital importance to biological processes. In this work, 2D regular rhombic nanocrystals ( RS -NC ) were fabricated through heterochiral self-discrimination between chiral polynuclear gold(I)-sulfido complex enantiomers, [(R-BINAP)₄Au₁₀S₄]Cl₂ ( R -Au₁₀ ) and [(S-BINAP)₄Au₁₀S₄]Cl₂ ( S -Au₁₀ ), in MeOH without the need for any surfactants or templates. The monitoring of nanocrystals (NCs) formation by TEM and DLS has uncovered the self-assembly process and shape evolution of the NCs and revealed a screw-dislocation dictated spiral growth of the rhombic NCs. Upon addition of chiral anions, the morphology of the gold NCs was found to change from rhombic to strip and quasi-hexagonal nanosheets, arising from reverse and rotational layer-by-layer stacking to give the bilayer NCs. By applying a high temperature, rhombic gold nanoisland films were obtained from the rhombic NCs. The current study has provided a simple strategy towards the construction of regular geometric 2D NCs as well as their chiral anion-tuned and reverse and rotational stacking-determined morphology change by heterochiral self-discrimination.     

超声化学法制备BaF_2纳米粒子及纳米方块

<正>0引言BaF2的用途非常广泛,可用于光学玻璃、陶瓷色料、玻璃光导纤维、激光发生器、助熔剂及防腐剂等。BaF2是最快的闪烁体,在核物理和核技术中用来检测γ射线和带电粒子[1]。将掺杂稀土金属的纳米BaF2粒子嵌入有机或玻璃基体以发挥其发光性能的研究越来越引起重视[2]。碱土氟化物和许多半导体的晶格匹配性良好,可以用不同碱土氟化物层来连接晶格常数不同的半导体[3]。     

Cysteamine-modified ZIF-8 colloidal building blocks: Direct assembly of nanoparticulate MOF films on gold surfaces via thiol chemistry

Chemical modification of metal organic framework (MOF) nanocrystal colloids was used to endow them with chemical affinity for gold substrates. Modified nanocrystals were then used as building blocks for rapid and selective self-assembly of porous films. Cysteamine (Cys, 2-aminoetanethiol) was chosen as both chemical modulator and functionalizing agent of Zeolite Imidazolate Framework-8 (ZIF-8) MOF nanocrystals. Important parameters such as the impact of the modulator on the range of nanocrystals stability, size, polydispersity, morphology, and crystalline structure were assessed via both, small and wide angle x-ray scattering (SAXS and WAXS). Cysteamine modified ZIF-8 nanocrystals were assembled into films over conductive Au substrates and film growth was followed in-situ with Quartz Crystal Microbalance (QCM). Thiol moieties exposed out of the ZIF-8 surface after cysteamine modification, results in the formation of thiol bonds with Au conductive substrates as shown via Cyclic Voltammetry experiments. The strategy here presented allows for the synthesis of pre-designed building blocks for MOF films on metal surfaces.     

Fabrication of Au-Pd core-shell heterostructures with systematic shape evolution using octahedral nanocrystal cores and their catalytic activity

By using octahedral gold nanocrystals with sizes of approximately 50 nm as the structure-directing cores for the overgrowth of Pd shells, Au-Pd core-shell heterostructures with systematic shape evolution can be directly synthesized. Core-shell octahedra, truncated octahedra, cuboctahedra, truncated cubes, and concave cubes were produced by progressively decreasing the amount of the gold nanocrystal solution introduced into the reaction mixture containing cetyltrimethylammonium bromide (CTAB), H(2)PdCl(4), and ascorbic acid. The core-shell structure and composition of these nanocrystals has been confirmed. Only the concave cubes are bounded by a variety of high-index facets. This may be a manifestation of the release of lattice strain with their thick shells at the corners. Formation of the [CTA](2)[PdBr(4)] complex species has been identified spectroscopically. Time-dependent UV-vis absorption spectra showed faster Pd source consumption rates in the growth of truncated cubes and concave cubes, while a much slower reduction rate was observed in the generation of octahedra. The concave cubes and octahedra were used as catalysts for a Suzuki coupling reaction. They can all serve as effective and recyclable catalysts, but the concave cubes gave higher product yields with a shorter reaction time attributed to their high-index surface facets. The concave cubes can also catalyze a wide range of Suzuki coupling reactions using aryl iodides and arylboronic acids with electron-donating and -withdrawing substituents.     

Parametric study on electrochemical deposition of copper nanoparticles on an ultrathin polypyrrole film deposited on a gold film electrode

Monoshaped and monosized copper nanostructured particles have been prepared by potentiostatic electrochemical deposition on an ultrathin polypyrrole (PPY) film, electrochemically grown on a Si(100) substrate sputter-coated with a thin gold film or gold-film electrode (GFE). The crystal size and the number density of the copper nanocrystals have been examined by varying several deposition parameters, including the thickness of the gold film, the PPY film thickness, the applied potential, and the Cu2+ and the electrolyte concentrations for copper deposition. Optimal conditions for uniform growth ofnanocrystals well-dispersed on the GFE have been determined, along with insight into the mechanism of crystal growth. A minimum gold film thickness of 80 nm is required to eliminate the effects of the gold-silicon interface. The PPY film thickness and homogeneity principally affect the shape uniformity of the nanocrystals, while the copper deposition potential could be used to regulate the size and number density of the nanocrystals. Both the Cu2+ and electrolyte concentrations are also found to play important roles in controlling the electrodeposition of nanocrystal growth.