Coordination Assembly of Discoid Nanoparticles

Supramolecular chemistry utilizes coordination bonds to assemble molecular building blocks into a variety of sophisticated constructs. However, traditional coordination assemblies are based on organic compounds that have limited ability to transport charge. Herein, we describe coordination assembly of anisotropic FeS₂ pyrite nanoparticles (NPs) that can facilitate charge transport. Zn²⁺ ions form supramolecular complexes with carboxylate end‐groups on NP surface, leading to multiparticle sheets with liquid‐crystal‐like organization. Conductivity and Hall carrier mobility of the p‐type layered semiconductor films with Zn²⁺ coordination bridging exceed those known for coordination compounds, some by several orders of magnitude. The nanoscale porosity of the assembled sheets combined with fast hole transport leads to high electrocatalytic activity of the NP films. The coordination assembly of NPs embraces the versatility of several types of building blocks and opens a new design space for self‐organized materials combining nanoscale and supramolecular structural motifs.     

"Lens" effect in directed assembly of nanowires on gradient molecular patterns

We report a new phenomenon, named here as the "lens" effect, in the directed-assembly process of nanowires (NWs) on self-assembled monolayer (SAM) patterns. In this process, the adsorption of NWs is focused in the nanoscale regions at the center of microscale SAM patterns with gradient surface molecular density just like an optical lens focuses light. As a proof of concepts, we successfully demonstrated the massive assembly of V2O5 NWs and single-walled carbon nanotubes (swCNTs) with a nanoscale resolution using only microscale molecular patterning methods. This work provides us with important insights about the directed-assembly process, and from a practical point of view, it allows us to generate nanoscale patterns of NWs over a large area for mass fabrication of NW-based devices.     

纳米级无机聚钼酸盐“二级有序聚集体”

介绍了纳米级水溶性无机聚钼酸盐分子的逐步生长合成, 对近年来水溶液中纳米级无机聚钼酸盐分子的奇特自聚集行为进行了简述, 从两亲分子“有序聚集体”概念的角度, 提出了水溶性纳米级无机聚钼酸盐“二级有序聚集体”的概念.     

Modulating the stacking modes of nanosized metal–organic frameworks by morphology engineering for isomer separation

Modulating different stacking modes of nanoscale metal–organic frameworks (MOFs) introduces different properties and functionalities but remains a great challenge. Here, we describe a morphology engineering method to modulate the stacking modes of nanoscale NU-901. The nanoscale NU-901 is stacked through solvent removal after one-pot solvothermal synthesis, in which different morphologies from nanosheets (NS) to interpenetrated nanosheets (I-NS) and nanoparticles (NP) were obtained successfully. The stacked NU-901-NS, NU-901-I-NS, and NU-901-NP exhibited relatively aligned stacking, random stacking, and close packing, respectively. The three stacked nanoscale NU-901 exhibited different separation abilities and all showed better performance than bulk phase NU-901. Our work provides a new morphology engineering route for the modulation of the stacking modes of nano-sized MOFs and improves the separation abilities of MOFs.

A morphology engineering method was utilized to modulate the stacking modes of three nano-NU-901 materials, leading to different separation abilities for isomers.     

Relative stability of icosahedral and cuboctahedral metallic nanoparticles

The size and form of metallic nanoparticles (NPs) significantly affects their adsorptive, chemical, and catalytic activity. One of the most interesting nanoscale size effects is the transition from icosahedral to octahedral forms with growth in the NP size. We compared the stability of icosahedral, decahedral and cuboctahedral NPs made from eight metals Ni, Cu, Rh, Pd, Ag, Ir, Pt, and Au using the local optimization of total energy, which was computed from the tight-binding second moment approximation and quantum Sutton–Chen potentials. The obtained results predicted that the icosahedral form would be most stable for Ni, and least stable for Au. For Rh, and especially for Ir, a strong dependency of the stability of the different forms on the NP size was revealed.     

Hierarchical nanoparticle/block copolymer surface features via synergistic self-assembly at the air-water interface

This work demonstrates the first example of the controlled organization of semiconducting nanoparticles (NPs) using amphiphilic block copolymer self-assembly at the air-water interface. Preferential interactions between polystyrene-functionalized NPs and the polystyrene block of an amphiphilic polystyrene-b-poly(ethylene oxide) block copolymer result in synergistic self-assembly at the air-water interface, forming a range of highly stable one-dimensional NP/polymer surface features, including branched nanowires, nanocables up to 100 microm in length, and nanowires with nanoring connectors. This strategy offers new routes to hierarchical hybrid assemblies with potential photonics applications because the nanoscale organization of NPs is coupled to features with dimensions that are commensurate with optical wavelengths.     

Nanoscale-enhanced Ru(bpy)3(2+) electrochemiluminescence labels and related aptamer-based biosensing system

A unique multilabeling at a single-site protocol of the Ru(bpy)(3)(2+) electrochemiluminescence (ECL) system is proposed. Nanoparticles (NPs) were used as assembly substrates to enrich ECL co-reactants of Ru(bpy)(3)(2+) to construct nanoscale-enhanced ECL labels. Two different kinds of NP substrates [including semiconductor NPs (CdTe) and noble metal NPs (gold)] capped with 2-(dimethylamino)ethanethiol (DMAET) [a tertiary amine derivative which is believed to be one of the most efficient of co-reactants of the Ru(bpy)(3)(2+) system] were synthesized through a simple one-pot synthesis method in aqueous media. Although both CdTe and gold NPs realized the enrichment of ECL co-reactants, they presented entirely different ECL performances as nanoscale ECL co-reactants of Ru(bpy)(3)(2+). The different effects of these two NPs on the ECL of Ru(bpy)(3)(2+) were studied. DMAET-capped CdTe NPs showed enormous signal amplification of Ru(bpy)(3)(2+) ECL, whereas DMAET-capped gold NPs showed a slight quenching effect of the ECL signal. DMAET-capped CdTe NPs can be considered to be excellent nanoscale ECL labels of the Ru(bpy)(3)(2+) system, as even a NP solution sample of 10(-18) M was still detectable after an electrostatic self-assembly concentration process. DMAET-capped CdTe NPs were further applied in the construction of aptamer-based biosensing system for proteins and encouraging results were obtained.     

Confined space design by nanoparticle self-assembly

Nanoparticle (NP) self-assembly has led to the fabrication of an array of functional nanoscale systems, having diverse architectures and functionalities. In this perspective, we discuss the design and application of NP suprastructures (SPs) characterized by nanoconfined compartments in their self-assembled framework, providing an overview about SP synthetic strategies reported to date and the role of their confined nanocavities in applications in several high-end fields. We also set to give our contribution towards the formation of more advanced nanocompartmentalized SPs able to work in dynamic manners, discussing the opportunities of further advances in NP self-assembly and SP research.

This perspective gives an outlook on the design of interparticle confined nanocavities in self-assembled NP systems and their functional relevance.     

Faraday rotation enhancement of gold coated Fe2O3 nanoparticles: comparison of experiment and theory

Understanding plasmonic enhancement of nanoscale magnetic materials is important to evaluate their potential for application. In this study, the Faraday rotation (FR) enhancement of gold coated Fe(2)O(3) nanoparticles (NP) is investigated experimentally and theoretically. The experiment shows that the Faraday rotation of a Fe(2)O(3) NP solution changes from approximately 3 rad/Tm to 10 rad/Tm as 5 nm gold shell is coated on a 9.7 nm Fe(2)O(3) core at 632 nm. The results also show how the volume fraction normalized Faraday rotation varies with the gold shell thickness. From the comparison of experiment and calculated Faraday rotation based on the Maxwell-Garnett theory, it is concluded that the enhancement and shell dependence of Faraday rotation of Fe(2)O(3) NPs is a result of the shifting plasmon resonance of the composite NP. In addition, the clustering of the NPs induces a different phase lag on the Faraday signal, which suggests that the collective response of the magnetic NP aggregates needs to be considered even in solution. From the Faraday phase lag, the estimated time of the full alignment of the magnetic spins of bare (cluster size 160 nm) and gold coated NPs (cluster size 90 nm) are found to be 0.65 and 0.17 μs. The calculation includes a simple theoretical approach based on the Bruggeman theory to account for the aggregation and its effect on the Faraday rotation. The Bruggeman model provides a qualitatively better agreement with the experimentally observed Faraday rotation and points out the importance of making a connection between component properties and the average "effective" optical behavior of the Faraday medium containing magnetic nanoparticles.     

Spontaneous self-organization enables dielectrophoresis of small nanoparticles and formation of photoconductive microbridges

Detailed understanding of the mechanism of dielectrophoresis (DEP) and the drastic improvement of its efficiency for small size-quantized nanoparticles (NPs) open the door for the convergence of microscale and nanoscale technologies. It is hindered, however, by the severe reduction of DEP force in particles with volumes below a few hundred cubic nanometers. We report here DEP assembly of size-quantized CdTe nanoparticles (NPs) with a diameter of 4.2 nm under AC voltage of 4-10 V. Calculations of the nominal DEP force for these NPs indicate that it is several orders of magnitude smaller than the force of the Brownian motion destroying the assemblies even for the maximum applied AC voltage. Despite this, very efficient formation of NP bridges between electrodes separated by a gap of 2 μm was observed even for AC voltages of 6 V and highly diluted NP dispersions. The resolution of this conundrum was found in the intrinsic ability of CdTe NPs to self-assemble. The species being assembled by DEP are substantially bigger than the individual NPs. DEP assembly should be treated as a process taking place for NP chains with a length of ~140 nm. The self-assembled chains increase the nominal volume where the polarization of the particles takes place, while retaining the size-quantized nature of the material. The produced NP bridges were found to be photoactive, producing photocurrent upon illumination. DEP bridges of quantum confined NPs can be used in fast parallel manufacturing of novel MEMS components, sensors, and optical and optoelectronic devices. Purposeful engineering of self-assembling properties of NPs makes possible further facilitation of the DEP and increase of complexity of the produced nano- and microscale structures.     

Synthesis of oligo(phenylene ethynylene)s with dendrimer "shells" for molecular electronics

Two series of oligo(phenylene ethynylene)s (OPEs) with different dendrimer side groups have been designed and synthesized. The molecules contain thiol groups at both ends to enable interconnection between nanoscale gapped metallic electrodes. The different dendrimer groups act as "shells", allowing tailoring to the nanoscopic environment surrounding the OPE "core". Meanwhile, the dendrimer shells also act as spacers for the precise control of the packing density and intermolecular interaction between the OPE cores. [structure: see text].     

Quantitative energy dispersive X-ray microanalysis of electron beam-sensitive alloyed nanoparticles.

An energy dispersive X-ray spectrometry (EDXS) method is developed to evaluate the composition of alloyed nanoparticles (NPs) where one of the alloying elements is removed under the electron beam during microanalysis with a transmission electron microscope (TEM). The method is demonstrated for alloyed Au-Ag NPs of a diameter ranging from 6 to 20 nm produced by laser evaporation of a water-suspended Ag-Au powder mixture of varying composition. Series of EDXS spectra are recorded for 30 NPs from samples with five different Ag:Au ratios revealing Ag depletion from NPs during electron irradiation. By studying the evolution of NPs composition as a function of dose, the initial Ag content for each NP is extrapolated. The rate of Ag depletion is discussed in terms of sputtering and knock-on damage. On average, approximately one Ag atom is lost from the NP for each Ag L X-ray detected. To assess the limitations of microanalysis in these sensitive nanoscale structures, the concept of detectability limit is adapted to our method. This benchmark is then evaluated for Ag in Au-Ag NPs of various sizes and acquisition times. This study should be regarded as a guide for the design of analytical TEM measurements of beam-sensitive NPs.     

Charge trapping and storage by composite P3HT/PC60BM nanoparticles investigated by fluorescence-voltage/single particle spectroscopy

Fluorescence-voltage/single particle spectroscopy (F-V/SPS) was employed to study exciton-hole polaron interactions and interfacial charge transfer processes for pure poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) and composite P3HT/PC(60)BM NPs in functioning hole-injection devices. F-V/SPS data collected on a particle-by-particle basis reveal an apparent bistability in the fluorescence-voltage modulation curves for composite NPs of P3HT and [6,6]-phenyl-C(61)-butyric acid methyl ester (PC(60)BM) that is absent for pure P3HT NPs. A pronounced deep trapping of free electrons photogenerated from the composite P3HT/PC(60)BM NPs at the NP/dielectric interface and hole trapping by fullerene anions in composite P3HT/PC(60)BM NPs under photoexcitation lies at the basis of this finding. The deep electron trapping effect reported here for composite conjugated polymer/fullerene NPs presents an opportunity for future application of these NPs in nanoscale memory and imaging devices.     

"Bottom-up" meets "top-down" assembly in nanoscale polyoxometalate clusters: self-assembly of [P4W52O178](24-) and disassembly to [P3W39O134](19-)

The pH-controlled assembly/disassembly of a nanoscale {P4W52O178}24- cluster at pH 2 to a {P4W44O152}20- cluster at pH 3-5 via a {P3W39O134}19- cluster species at pH 2-3 to finally give {P2W19O69(OH2)}14- at pH 6 is reported. This process can be traced in the solid state crystallographically and in solution using dynamic light scattering studies.     

"Three-dimensional hybridization" with polyvalent DNA-gold nanoparticle conjugates

We have determined the minimum number of base pairings necessary to stabilize DNA-Au NP aggregates as a function of salt concentration for particles between 15 and 150 nm in diameter. Significantly, we find that sequences containing a single base pair interaction are capable of effecting hybridization between 150 nm DNA-Au NPs. While traditional DNA hybridization involves two strands interacting in one dimension (1D, Z), we propose that hybridization in the context of an aggregate of polyvalent DNA-Au NP conjugates occurs in three dimensions (many oligonucleotides oriented perpendicular to the X, Y plane engage in base pairing), making nanoparticle assembly possible with three or fewer base pairings per DNA strand. These studies enabled us to compare the stability of duplex DNA free in solution and bound to the nanoparticle surface. We estimate that 4-8, 6-19, or 8-33 additional DNA bases must be added to free duplex DNA to achieve melting temperatures equivalent to hybridized systems formed from 15, 60, or 150 nm DNA-Au NPs, respectively. In addition, we estimate that the equilibrium binding constant (K(eq)) for 15 nm DNA-Au NPs (3 base pairs) is approximately 3 orders of magnitude higher than the K(eq) for the corresponding nanoparticle free system.     

Observation of size-independent effects in nanoparticle retention behavior during asymmetric-flow field-flow fractionation

In this work, we highlight the size-independent influence of the material properties of nanoparticles (NPs) on their retention behavior in asymmetric-flow field-flow fractionation (A4F) by comparing four NP populations with similar nominal size. The phenomena described here suggest there are limits to the effectiveness and accuracy of using a single type of NP standard (polystyrene beads most typically) in order to generically calibrate retention time in normal mode elution. The dual objectives of this paper are to (1) demonstrate the uncertainties resulting from current practice and (2) initiate a discussion of these effects and their origins. The results presented here illustrate clearly that the retention time is higher for metallic NPs relative to lower (bulk) density NPs. By modifying the fundamental field-flow fractionation equation to account for differences in particle density, we show that the effect of the gravitational force is finite but insignificant for NPs. We postulate that the observed material-dependent retention behavior may be attributed to differences in the attractive van der Waals force between the NPs and the accumulation wall (membrane surface). We hope that our results will stimulate discussion and reassessment of the calibration procedure, perhaps by more fully accounting for all influential material parameters relevant to the fractionation of nanoscale particles by A4F.     

基于分子间相互作用的纳米尺度分子传递

纳米尺度下的分子传递是以纳米先进材料为导向的材料化学工程学科所面临的关键科学问题之一.借鉴分子热力学的建模研究思路研究分子传递,从分子之间相互作用出发,结合分子模拟技术,有望最终建立理论模型,实现分子传递的定量预测.本文通过几个研究实例初步探索了如何从分子间相互作用出发开展纳米尺度下分子传递的研究,利用分子模拟手段解析纳米尺度下特殊的微结构,并以此为基础进而实现对分子传递行为的调控和预测,指导具有丰富纳米结构的膜材料以及催化材料的设计和应用.     

Physical-chemical aspects of protein corona: relevance to in vitro and in vivo biological impacts of nanoparticles

It is now clearly emerging that besides size and shape, the other primary defining element of nanoscale objects in biological media is their long-lived protein ("hard") corona. This corona may be expressed as a durable, stabilizing coating of the bare surface of nanoparticle (NP) monomers, or it may be reflected in different subpopulations of particle assemblies, each presenting a durable protein coating. Using the approach and concepts of physical chemistry, we relate studies on the composition of the protein corona at different plasma concentrations with structural data on the complexes both in situ and free from excess plasma. This enables a high degree of confidence in the meaning of the hard protein corona in a biological context. Here, we present the protein adsorption for two compositionally different NPs, namely sulfonated polystyrene and silica NPs. NP-protein complexes are characterized by differential centrifugal sedimentation, dynamic light scattering, and zeta-potential both in situ and once isolated from plasma as a function of the protein/NP surface area ratio. We then introduce a semiquantitative determination of their hard corona composition using one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrospray liquid chromatography mass spectrometry, which allows us to follow the total binding isotherms for the particles, identifying simultaneously the nature and amount of the most relevant proteins as a function of the plasma concentration. We find that the hard corona can evolve quite significantly as one passes from protein concentrations appropriate to in vitro cell studies to those present in in vivo studies, which has deep implications for in vitro-in vivo extrapolations and will require some consideration in the future.     

Fluorescent core-shell silica nanoparticles: towards "Lab on a Particle" architectures for nanobiotechnology

Novel nanoscale fluorescent materials are integral to the progress of emergent fields such as nanobiotechnology and facilitate new research in a variety of contexts. Sol-gel derived silica is an excellent host material for creating fluorescent nanoparticles by the inclusion of covalently-bound organic dyes. Significant enhancements in the brightness and stability of organic dye emission can be achieved for silica-based core-shell nanoparticle architectures at length scales down to tens of nanometers with narrow size distributions. This tutorial review will highlight these findings and describe the evolution of the fluorescent core-shell silica nanoparticle concept towards integration of multiple functionalities including mesoporosity, metal nanoshells and quantitative chemical sensing. These developments point towards the development of "lab on a particle" architectures with promising prospects for nanobiotechnology, drug development and beyond.