Gold nanoparticle assemblies through hydrogen-bonded supramolecular mediators

The synthesis of spherical gold nanoparticle assemblies with multicomponent double rosette molecular boxes as mediators is presented. These nine-component hydrogen-bonded supramolecular structures held together by 36 hydrogen bonds induce gold nanoparticle assembly. The morphologies of the nanoparticle assemblies can be tuned easily by changing the quantity of the building block chemisorbed on the nanoparticle surface.     

Gold nanoparticle multilayer films based on surfactant films as a template: preparation, characterization, and application

Highly ordered gold nanoparticle multilayer films were achieved conveniently using didodecyldimethylammonium bromide (DDAB) films as a template. The template was produced by casting DDAB chloroform solution onto the surface of a (3-aminopropyl)trimethoxysilane-modified indium tin oxide substrate and then evaporating the organic solvent. Gold nanoparticle multilayer films were prepared by soaking the template in 2.6 nm colloidal gold solution for 120 min. The well-ordered superlattice structure of the DDAB template and the gold nanoparticle multilayer films was identified by x-ray diffraction. The characterizations of the gold nanoparticle multilayer films by UV-vis spectroscopy, atomic force microscopy, and cyclic voltammerty were described in detail. The application of the as-prepared gold nanoparticle multilayer films in surface-enhanced Raman spectroscopy (SERS) was investigated by using Rhodamine 6G as a probe molecule. It was found that the colloidal gold nanoparticle multilayer films exhibit remarkable enhancement ability and can be used as SERS substrates.     

Electrochemical Behaviors of Single Gold Nanoparticles

In this paper, the electrochemical behaviors of a single gold nanoparticle attached on a nanometer sized electrode have been studied. The single nanoparticle was characterized by using electrochemical methods. Since there is only one nanoparticle on the electrode, unarguable information for that sized particle could be obtained. Our preliminary results show that it becomes more difficult to oxidize gold nanoparticle or reduce gold nanoparticle oxide as the radius of the particle becomes smaller. Also, the peak potential of the reduction of gold nanoparticle oxide is proportional to the reciprocal of the radius of the particle.     

Switchable water absorption of paper via liquid flame spray nanoparticle coating

Surface wetting/anti-wetting and liquid absorption are relevant properties of many porous solids including paper and other cellulose-based materials. Here we demonstrate how surface wetting by water and water absorption of commercially available kraft paper can be altered by thin nanoparticle coatings fabricated by liquid flame spray in facile and continuous one-step process. Surface wettability and absorption properties of paper increased with silica and decreased with titania (TiO₂) nanoparticle coatings. Moreover, the water-repellent (superhydrophobic) TiO₂ nanoparticle coated paper could be switched to superhydrophilic and water absorbing by ultraviolet illumination. The experiments revealed that although surface wetting and liquid absorption of nanoparticle coated paper are strongly related to each other, they are two distinct phenomena which do not necessarily correlate. We propose wetting regimes on the nanoparticle coated paper samples on the basis of the experimental observations.     

Preparation of high-quality organic semiconductor nanoparticle films by solvent-evaporation-induced self-assembly

Organic semiconductor nanoparticles are expected to be used in organic optical and electronic devices due to their unique optical and electrical properties. However, no method has been reported for the preparation of high-quality organic nanoparticle films without remaining additives and being capable of dealing with binary nanoparticle blends. We developed a simple approach to fabricate high-quality organic semiconductor nanoparticle films from their aqueous solutions by solvent-evaporation-induced self-assembly. Only volatile solvents are employed in the nanoparticle solutions, so the self-assembled nanoparticle films are free of additives. Moreover, this method is also suitable for fabricating thin films containing binary nanoparticles. Therefore, it paves the way for potential applications of organic semiconductor nanoparticles in nanoscale optical and electronic devices.     

以DDAB为模板的银纳米粒子多层膜制备及其表面增强拉曼效应

通过离子交换和静电相互作用, 将银纳米粒子引入双十二烷基二甲基溴化铵(DDAB)模板中, 获得了有序的银纳米粒子多层膜. 用紫外-可见光谱(UV-Vis)、循环伏安(CV)和原子力显微镜(AFM)对其进行了表征, 并用小角X射线衍射(XRD)研究了DDAB模板和银纳米粒子多层膜的有序性结构. 以4-巯基吡啶(4-MPY)为探针分子研究了银纳米粒子多层膜在表面增强拉曼(SERS)方面的应用, 结果表明, 4-MPY吸附在银纳米粒子多层膜上呈现很强的SERS信号, 说明该多层膜可以用作高活性的SERS基底.     

Refractive index of sparse layers of adsorbed gold nanoparticles

Measurements are presented of the effective complex refractive index of a layer of gold nanoparticles adsorbed to a silicon wafer at low coverages. The measurements were made by means of variable-angle ellipsometry, and correlated with nanoparticle coverage determined from atomic force microscope images. The analysis establishes the effective refractive index of a uniform layer whose thickness equals the nanoparticle diameter. A simple empirical relationship is obtained for real component of refractive index as a function of the fractional nanoparticle coverage regardless of the nanoparticle size. The imaginary component also follows a simple relationship but only up to a certain coverage, above which it increases rapidly. These relationships may be useful in other contexts such as chemical or biosensors in which the nanoparticle coverage could be inferred from optical measurements such as ellipsometry, surface plasmon resonance spectroscopy, reflectometry, or interferometry.     

有机配体修饰纳米Al2O3的合成及性质研究

合成了以β-二酮配体3-甲基-1-苯基-4-(十八烷基酰基)吡唑啉酮-5(PMOP)修饰的Al2O3纳米粒子,并用IR、UV光谱、NMR和荧光光谱等手段进行了表征.修饰后的Al2O3纳米粒子能溶于氯仿、乙醇和甲苯等常见有机溶剂,并有较强的蓝色荧光.表明在一些无机纳米粒子的表面键合上有机配体后,可以产生新的光物理性质.修饰后的Al2O3纳米粒子还可作为支架材料用于准固态染料敏化纳米晶太阳能电池中.     

Bioavailability of nanoparticles in nutrient and nutraceutical delivery

The field of nanoparticle delivery systems for nutrients and nutraceuticals with poor water solubility has been expanding, almost exponentially, over the last five years, and some of these technologies are now in the process of being incorporated in food products. The market projections for these technologies suggest a multifold increase in their commercial potential over the next five years. The interest in the pharmaceutical and food-related applications of these technologies has sparked tremendous developments in mechanical (top-down) and chemical (bottom-up) processes to obtain such nanoparticle systems. Mechanical approaches are capable of producing nanoparticles, typically in the 100–1000 nm range, whereas chemical methods tend to produce 10–100 nm particles. Despite these technological developments, there is a lack of information regarding the basis of design for such nanoparticle systems. Fundamental thermodynamic and mass transfer equations reveal that, in order to generate a broad spectrum delivery system, nanoparticles with 100 nm diameter (or less) should be produced. However, experimental data reveal that, in some cases, even nanoparticles in the 100–1000 nm range are capable of producing substantial improvement in the bioavailability of the active ingredients. In most cases, this improvement in bioavailability seems to be linked to the direct uptake of the nanoparticle. Furthermore, direct nanoparticle uptake is controlled by the size and surface chemistry of the nanoparticle system. The use of this direct nanoparticle uptake, in particular for soluble but poorly absorbed ingredients, is one of the areas that needs to be explored in the future, as well as the potential side effects of these nanoparticle carriers.     

Functionalization of monodisperse magnetic nanoparticles

We report a new strategy for the preparation of monodisperse, water-soluble magnetic nanoparticles. Oleic acid-stabilized magnetic nanocrystals were prepared by the organic synthesis route proposed by Sun et al. (J. Am. Chem. Soc. 2004, 126, 273.), with size control obtained via seeded-mediated growth. The oleic groups initially present on the nanoparticle surfaces were replaced via ligand exchange reactions with various capping agents bearing reactive hydroxyl moieties. These hydroxyl groups were (i) exploited to initiate ring opening polymerization (ROP) of polylactic acid from the nanoparticle surfaces and (ii) esterified by acylation to permit the addition of alkyl halide moieties to transform the nanoparticle surfaces into macroinitiators for atom transfer radical polymerization (ATRP). By appropriate selection of the ligand properties, the nanoparticle surfaces can be polymerized in various solvents, providing an opportunity for the growth of a wide variety of water-soluble polymers and polylectrolyte brushes (both cationic and anionic) from the nanoparticle surfaces. The nanoparticles were characterized by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), electron microscopy, and light scattering. Light scattering measurements indicate that the nanoparticles are mostly present as individual nonclustered units in water. With pH-responsive polymers grown on the nanoparticle surfaces, reversible aggregation of nanoparticles could be induced by suitable swings in the pH between the stable and unstable regions.     

Biomimetic assembly of polypeptide-stabilized CaCO(3) nanoparticles

In this paper, we report a simple polypeptide-directed strategy for fabricating large spherical assembly of CaCO(3) nanoparticles. Stepwise growth and assembly of a large number of nanoparticles have been observed, from the formation of an amorphous liquidlike CaCO(3)-polypeptide precursor, to the crystallization and stabilization of polypeptide-capped nanoparticles, and eventually, the spherical assembly of nanoparticles. The "soft" poly(aspartate)-capping layer binding on a nanoparticle surface resulted in the unusual soft nature of nanoparticle assembly, providing a reservoir of primary nanoparticles with a moderate mobility, which is the basis of a new strategy for reconstructing nanoparticle assembly into complex nanoparticle architectures. Moreover, the findings of the secondary assembly of nanoparticle microspheres and the morphology transformation of nanoparticle assembly demonstrate a flexible and controllable pathway for manipulating the shapes and structures of nanoparticle assembly. In addition, the combination of the polypeptide with a double hydrophilic block copolymer (DHBC) allows it to possibly further control the shape and complexity of the nanoparticle assembly. A clear perspective is shown here that more complex nanoparticle materials could be created by using "soft" biological proteins or peptides as a mediating template at the organic-inorganic interface.     

A facile one-pot method to fabricate gold nanoparticle chains with dextran

A biocompatible water-soluble dextran has been used for controllable one-dimensional assembly of gold nanoparticles via a one-pot method.Long gold nanoparticle chains with good dispersion in water could be easily obtained after adding dextran into the mixture of HAuCl 4 and sodium citrate.The measurements of scanning electron microscopy(SEM) and dynamic light scattering(DLS) confirmed the formation of gold nanoparticle chains.The morphology and dispersion properties of gold nanoparticle chains could be tuned by adjustment of the reagent ratio,stirring speed,and reaction time.     

Stimuli induced structural changes of gold nanoparticle assemblies having sequential alternating amphiphilic peptides at the surface

Gold nanoparticles having sequential alternating amphiphilic peptide chains, Phe-(Leu-Glu)8, on the surface have been prepared. We describe structural control of the amphiphilic peptide coated gold nanoparticle assembly by a conformational transition of the surface peptides. Under the acidic condition, the conformation of the surface amphiphilic peptide was converted to a beta-sheet structure from an aggregated alpha-helix by incubation. Under this condition, the amphiphilic peptide coated gold nanoparticles formed a nanosheet assembly. The plasmon absorption maximum of the gold nanoparticles shifted to a shorter wavelength with the formation of the beta-sheet assembly of the surface peptide. This suggests that the structure of the peptide coated gold nanoparticle assembly could be controlled by the conformational transition of the surface peptide. Furthermore, the core gold nanoparticle could be fixed in the beta-sheet assembly in the state that stood alone. This system may be useful for novel molecular devices that exhibit quantized properties.     

Enhanced ferroelectric phase content of polyvinylidene difluoride fibers with the addition of magnetic nanoparticles

Polyvinylidene difluoride (PVDF) fibers with continuously dispersed ferrite (Ni 0.5Zn 0.5Fe 2O 4) nanoparticles were prepared by electrospinning from dimethyl formamide (DMF) solutions. The effects of the electrospinning processing conditions and nanoparticle loading on the formation of the alpha, beta, and gamma phases of PVDF were studied using infrared spectroscopy and differential scanning calorimetry. The amount of the ferroelectric beta and gamma phases present in the fibers was found to increase with increased nanoparticle loading. We have shown that the formation of PVDF phases with extended chain conformations can be enhanced by the addition of a well-dispersed nanoparticle phase. At increased nanoparticle loadings, the alpha phase is completely converted to the more extended beta and gamma phases.     

Two-dimensional self-assemblies of silica nanoparticles formed using the "bubble deposition technique"

Two-dimensional silica nanoparticle assemblies were obtained by deposition of bubble made from a surfactant solution containing nanoparticles onto hydrophobic silicon substrate. The morphologies of the nanoparticle assemblies can be finely controlled by several experimental parameters, including surfactant concentration, nanoparticle concentration, and deposition time. Monolayer of nanoparticles with surface coverage of about 100% can be obtained under appropriate conditions. The method can also be applied to another hydrophobic substrate, HMDS (hexamethyldisilazane)-modified silicon substrate. Furthermore, it can be applied directly to lithography patterned substrates, meaning a high compatibility with the well-developed conventional top-down approaches to nanodevices. This bubble deposition technique is expected to be a promising method in the field of nano-object assembly and organization and has great application potentials.     

Control of Nanoparticle Release Kinetics from 3D Printed Hydrogel Scaffolds

The convergence of biofabrication with nanotechnology is largely unexplored but enables geometrical control of cell‐biomaterial arrangement combined with controlled drug delivery and release. As a step towards integration of these two fields of research, this study demonstrates that modulation of electrostatic nanoparticle–polymer and nanoparticle–nanoparticle interactions can be used for tuning nanoparticle release kinetics from 3D printed hydrogel scaffolds. This generic strategy can be used for spatiotemporal control of the release kinetics of nanoparticulate drug vectors in biofabricated constructs.     

Thermodiffusion in model nanofluids by molecular dynamics simulations

In this work, a new algorithm is proposed to compute single particle (infinite dilution) thermodiffusion using nonequilibrium molecular dynamics simulations through the estimation of the thermophoretic force that applies on a solute particle. This scheme is shown to provide consistent results for model nanofluids in the liquid state (spherical nonmetallic nanoparticles+Lennard-Jones fluid) where it appears that thermodiffusion amplitude, as well as thermal conductivity, decreases with nanoparticle concentration. Then, by changing the nature of the nanoparticle (size, mass, and internal stiffness) and that of the solvent (quality and viscosity), various trends are exhibited. In all cases, the single particle thermodiffusion is positive, i.e., the nanoparticle tends to migrate toward the cold area. The single particle thermal diffusion coefficient is shown to be independent of the size of the nanoparticle (diameter of 0.8-4 nm), whereas it increases with the quality of the solvent and is inversely proportional to the viscosity of the fluid. In addition, this coefficient is shown to be independent of the mass of the nanoparticle and to increase with the stiffness of the nanoparticle internal bonds. Besides, for these configurations, the mass diffusion coefficient behavior appears to be consistent with a Stokes-Einstein-like law.     

Postsynthesis racemization and place exchange reactions. Another step to unravel the origin of chirality for chiral ligand-capped gold nanoparticles

We examine how postsynthesis nanoparticle ligand shell modifications as a general approach can help in the understanding of currently proposed mechanisms for gold nanoparticle chirality. We compare the CD response of chirally decorated mixed-monolayer-protected gold nanoparticles synthesized in situ with quasi-identical gold nanoparticles either prepared by place exchange reactions or subjected to an aqueous base, resulting in partial hydrolysis and simultaneous partial racemization. We find that the CD response at wavelengths where the free chiral ligand does not absorb strongly depends on the preparation conditions, i.e., in situ synthesis vs place exchange, and that postsynthesis racemization of the chiral ligand produces racemic nanoparticles with no CD response, i.e., no induction of a chiral bias during reductive nanoparticle formation. Considering all experimental results for the described gold nanoparticle system with a C12H24 spacer between the nanoparticle surface and chiral center, the so-called "vicinal effect" with the formation of a supramolecular assembly of the chiral moieties seems to be active. Finally, we argue that postsynthesis nanoparticle ligand shell modifications such as racemization and/or place exchange reactions are very powerful tools to unravel contributions of the different gold nanoparticle chirality mechanisms.     

氯金酸-罗丹明S缔合纳米微粒体系的共振散射增强与荧光猝灭研究

在0．2mol/L HCl介质中，罗丹明S(RDS)分别在520nm和550nm处有一个吸收峰和荧光峰。当有Au(Ⅲ）存在时，Au（Ⅲ）与Cl^-形成AuCl4^-，AuCl^-与RDS^ 借助于静电引力形成疏水性的AuCl4-RDS缔合物分子。AuCl4-RDS分子间存在较强的分子间作用力和疏水作用力而生成(AuCl4-RDS)。缔合纳米微粒，粒径为45nm。在360nm产生瑞利散射峰，在600nm产生共振散射峰。由于纳米微粒形成后，只有裹露在(AuCl4-RDS)n纳米微粒界面的RDS荧光分子才能吸收激发光子跃迁到激发态，进而返回基态产生荧光。而体相的RDS荧光分子无法与激发光作用产生荧光，即受激RDS分子数大为降低，故550nm荧光峰和520nm吸收峰的降低。当缔合纳米微粒体系加入乙醇后，体系的红紫色和共振散射峰消失，吸收峰和荧光峰恢复，由于乙醇致使(AuCl4-RDS)。纳米微粒分解为AuCl4-RDS分子。结果表明：红紫色(AuCl4-RDS)n纳米粒子的形成是其共振散射增强、荧光猝灭和产生共振散射峰的根本原因。     

A discrete interaction model/quantum mechanical method to describe the interaction of metal nanoparticles and molecular absorption

A frequency-dependent quantum mechanics/molecular mechanics method for the calculation of response properties of molecules adsorbed on metal nanoparticles is presented. This discrete interaction model/quantum mechanics (DIM/QM) method represents the nanoparticle atomistically, thus accounting for the local environment of the nanoparticle surface on the optical properties of the adsorbed molecule. Using the DIM/QM method, we investigate the coupling between the absorption of a silver nanoparticle and of a substituted naphthoquinone. This system is chosen since it shows strong coupling due to a molecular absorption peak that overlaps with the plasmon excitation in the metal nanoparticle. We show that there is a strong dependence not only on the distance of the molecule from the metal nanoparticle but also on its orientation relative to the nanoparticle. We find that when the transition dipole moment of an excitation is oriented towards the nanoparticle there is a significant increase in the molecular absorption as a result of coupling to the metal nanoparticle. In contrast, we find that the molecular absorption is decreased when the transition dipole moment is oriented parallel to the metal nanoparticle. The coupling between the molecule and the metal nanoparticle is found to be surprisingly long range and important on a length scale comparable to the size of the metal nanoparticle. A simple analytical model that describes the molecule and the metal nanoparticle as two interacting point objects is found to be in excellent agreement with the full DIM/QM calculations over the entire range studied. The results presented here are important for understanding plasmon-exciton hybridization, plasmon enhanced photochemistry, and single-molecule surface-enhanced Raman scattering.