Magnetic self-assembly of gold nanoparticle chains using dipolar core-shell colloids

The preparation of gold nanoparticle (AuNP) assemblies was conducted by the synthesis and dipolar assembly of ferromagnetic core-shell nanoparticles composed of AuNP cores and cobalt NP shells. Dissolution of metallic Co phases with mineral acids afforded self-assembled AuNP chains and bracelets.     

Spatially controlled SERS patterning using photoinduced disassembly of gelated gold nanoparticle aggregates

Controlling the assembly of the nanoparticles is important because the optical properties of noble metal nanoparticles, such as the surface plasmon resonance (SPR) and surface-enhanced Raman scattering (SERS), are critically dependent on interparticle distances. Among many approaches available, light-induced disassembly is particularly attractive because it enables spatial modification of the optical properties of nanoparticle assemblies. In this study, we prepare gold nanoparticle (AuNP) aggregates in a gel matrix. Irradiation of the gelated AuNP aggregates at 532 nm leads to the disassembly of the aggregates, changing the color (SPR) from dark blue to red and extinguishing the SERS signal along the irradiated pattern, which opens the possibility of facile fabrication of spatially controlled SERS-generating microstructures. The photoinduced disassembly of the AuNP aggregates in solution is also investigated using UV-vis spectroscopy and transmission electron microscopy.     

Assembly of DNA-functionalized gold nanoparticles studied by UV/Vis-spectroscopy and dynamic light scattering

The DNA mediated assembly of complementary DNA-functionalized gold nanoparticles (DNA-AuNP) was investigated by means of UV/Vis-spectroscopy and Dynamic Light Scattering (DLS). The melting temperature of the aggregates was determined to be T(m) = 31 degrees C. Characterization of the assembly at 20 degrees C, 25 degrees C and 30 degrees C showed a decrease of the initial assembly growth rate with increasing temperature. The correlation of the wavelengths at the absorbance maxima lambda(max) and the hydrodynamic radii R(h) of the AuNP assemblies proved the dependence of the optical properties on the assembly size while at higher assembly temperature (30 degrees C) a larger redshift of lambda(max) with increasing R(h) was observed than at lower temperatures. This tendency might give information about the dependence of the internal structure of the DNA-AuNP assemblies on assembly temperature. It is assumed that at higher temperatures more compact assemblies are built than at lower temperatures of 20 degrees C and 25 degrees C. To the best of our knowledge, this is the first systematic time-resolved in situ investigation of DNA-mediated AuNP assembly by UV/Vis-spectroscopy and DLS.     

A Spatially Programmable DNA Nanorobot Arm to Modulate Anisotropic Gold Nanoparticle Assembly by Enzymatic Excision

Programmable assembly of gold nanoparticle superstructures with precise spatial arrangement has drawn much attention for their unique characteristics in plasmonics and biomedicine. Bio-inspired methods have already provided programmable, molecular approaches to direct AuNP assemblies using biopolymers. The existing methods, however, predominantly use DNA as scaffolds to directly guide the AuNP interactions to produce intended superstructures. New paradigms for regulating AuNP assembly will greatly enrich the toolbox for DNA-directed AuNP manipulation and fabrication. Here, we developed a strategy of using a spatially programmable enzymatic nanorobot arm to modulate anisotropic DNA surface modifications and assembly of AuNPs. Through spatial controls of the proximity of the reactants, the locations of the modifications were precisely regulated. We demonstrated the control of the modifications on a single 15 nm AuNP, as well as on a rectangular DNA origami platform, to direct unique anisotropic AuNP assemblies. This method adds an alternative enzymatic manipulation to DNA-directed AuNP superstructure assembly.     

Crystallization-driven Nanoparticle Crystalsomes

Nanoparticle (NP) assembly has been extensively studied, and a library of NP superstructures has been synthesized. These intricate structures show unique collective optical, electronic, and magnetic properties. In this work, we report a bottom-up approach for fabricating spherical gold nanoparticle (AuNP) assemblies that mimic colloidosomes. Co-crystallization of lipoic acid-end-functionalized poly(ethylene oxide) (PEO) and AuNPs in solution via a self-seeding method led to the formation of hollow spherical NP assemblies named nanoparticle crystalsomes (NPCs). Due to the spherical shape, the translational symmetry of PEO crystals is broken in NPCs, which can be attributed to the competition between NP close packing and polymer crystallization. This was confirmed by tuning the NPC morphology via varying the self-seeding temperature, crystallization temperature, and PEO molecular weight. We envisage that this strategy paves the way to attaining exquisite morphological control of NP assemblies with broken translational symmetry.     

NaBH4-induced assembly of immobilized Au nanoparticles into chainlike structures on a chemically modified glass surface

A facile method of obtaining chainlike assemblies of gold nanoparticles (AuNPs) on a chemically modified glass surface based on NaBH(4) treatment is developed. Citrate-stabilized AuNPs (17 nm) are immobilized on a glutaraldehyde-functionalized glass surface and assembled into chainlike structures after treatment with aqueous sodium borohydride (NaBH(4)) solution. The production and morphology of the AuNP chainlike assemblies are controlled by the density of the immobilized NPs, the concentration of NaBH(4) solution, and the treatment time. The AuNP assemblies are stable in water and can undergo drying. X-ray photoelectron spectroscopic data show that the number of citrate ions on the AuNPs decreased by 43% after treatment with 5 mg/mL NaBH(4) solution. The NaBH(4)-induced partial removal of the citrate ions and the roughness of the glass surface greatly affect the binding force of AuNPs on the substrate. The immobilized AuNPs begin to move at the solid-liquid interface without desorbing when the strength of the binding force was decreased. These mobile NPs form chainlike assemblies under the driving force of van der Waals interaction and diffusion. This interface-based formation of chainlike assemblies of AuNPs may provide a simple protocol for the 1D assembly of other Au-coated colloidal nanoparticles.     

Nanowires of 3-D cross-linked gold nanoparticle assemblies behave as thermosensors on silicon substrates

In this study, we used a novel fabrication process, involving electron beam lithography and oxygen plasma treatment, to generate line and dot patterns of (3-mercaptopropyl)trioxysilane units over a large area of the Si(100) surface for gold nanoparticle (AuNP) immobilization. We synthesized the AuNPs in a two-phase system for assembly onto the Si substrate through coordination to the thiol groups of the protecting organic shell patterns. The resulting bottom layer of AuNPs was then treated with 1,6-hexanedithiol to generate thiol groups on their surfaces, thereby allowing the bottom-up construction of multiple layers of three-dimensional cross-linked AuNP assemblies, so-called poly(AuNP), linked directly to the Si substrate. We fabricated nanowires of cross-linked three-layer poly(AuNP) over large areas, with resolutions ranging from 200?nm to 10???m. The nanowires of the poly(AuNP) underwent dramatic changes in their electrical resistivities and morphologies when melting began at a temperature of 140°C. For example, the resistivity of the nanowires assembled from three layers of poly(AuNP) at a width of 1???m increased rapidly from 8.99?×?10^?C4 to 9,471??? m upon increasing the temperature from room temperature to 140°C. Such microwires assembled from lines of poly(AuNP) might, therefore, be applicable as thermosensors on Si surfaces in devices miniaturized to the nanoscale.     

Hybridization chain reaction triggered controllable one-dimensional assembly of gold nanoparticles

Assembling and ordering nanomaterials into desirable patterns are considerably significant, since the properties of nanomaterials depend not only on the size and shape, but also on the spatial arrangement among the collective building blocks. In this work, the DNA self-assembly technology of hybridization chain reaction (HCR) provided a convenient method to yield long double-strand DNA (dsDNA) to install gold nanoparticles (AuNPs) into one dimensional assembly along the skeleton of dsDNA. Interestingly, the tunable length of AuNPs assemblies along dsDNA chain could be achieved by adjusting the reaction time of HCR, which is based on the formation of covalent bond between Au and the -SH group of DNA. Compared with weak light scattering of single AuNP, these AuNPs assemblies could be clearly imaged under the dark field microscopy, indicating that the light scattering was greatly improved after assembling.     

Self‐Organization of Gold Nanoparticle Assemblies with 3D Spatial Order and Their External Stimuli Responsiveness

Gold nanoparticles (AuNP) with pyridyl end‐capped polystyrenes (PS‐4VP) as “quasi‐monodentate” ligands self‐assemble into ordered PS‐4VP/AuNP nanostructures with 3D hexagonal spatial order in the dried solid state. The key for the formation of these ordered structures is the modulation of the ratio AuNP versus ligands, which proves the importance of ligand design and quantity for the preparation of novel ordered polymer/metal nanoparticle conjugates. Although the assemblies of PS‐4VP/AuNP in dispersion lack in high dimensional order, strong plasmonic interactions are observed due to close contact of AuNP. Applying temperature as an external stimulus allows the reversible distortion of plasmonic interactions within the AuNP nanocomposite structures, which can be observed directly by naked eye. The modulation of the macroscopic optical properties accompanied by this structural distortion of plasmonic interaction opens up very interesting sensoric applications.

     

Applications of vectorized gold nanoparticles to the diagnosis and therapy of cancer

This critical review focuses on the anti-cancer fight using gold nanoparticles (AuNPs) functionalized with chemotherapeutic drugs in so-called "complexes" (supramolecular assemblies) and "conjugates" (covalent assemblies) as vectors. There is a considerable body of recent literature on various tumor-imaging techniques using the surface plasmon band (SPB) and the "passive" and "active" vectorization of anti-cancer drugs. This article reviews the main concepts and the most recent literature data with emphasis on AuNP preparation, cytotoxicities and use in selective targeting of cancer cells with over-expressed receptors for diagnosis and therapy (108 references).     

Layer-by-layer assembled gold nanoparticle films on amine-terminated substrates

This work reports the fabrication and characterization of multilayered gold nanoparticle (AuNP) thin films on aminosilane functionalized substrates. The films are fabricated via layer-by-layer (LbL) assembly using as-synthesized, un-modified AuNPs and poly(allylamine hydrochloride) as the building blocks. While most literature reports that AuNP based LbL assemblies are constructed with a single interlayer binding force, this work shows that both coordination and electrostatic interaction are involved in the process of assembly based on X-ray photoelectron spectroscopic results. The stepwise film growth behavior is demonstrated by atomic force spectroscopy and UV-vis spectroscopy. It is found that the particles agglomerate with each other and form large clusters when the number of assembled layers increases.     

Gold Nanoparticle Assemblies on Surfaces: Reactivity Tuning through Capping‐Layer and Cross‐Linker Design

The immobilization of metal nanoparticles (NPs) with molecular control over their organization is challenging. Herein, we report the formation of molecularly cross‐linked AuNP assemblies using a layer‐by‐layer approach. We observed four types of assemblies: 1) small aggregates of individual AuNPs, 2) large aggregates of individual AuNPs, 3) networks of fused AuNPs, and 4) gold islands. Interestingly, these assemblies with the different cross‐linkers and capping layers represent different stages in the complete fusion of AuNPs to afford islands of continuous gold. We demonstrate that the stability toward fusion of the nanoparticles of the on‐surface structures can be controlled by the reactivity of the cross‐linkers and the hydrophilicity/hydrophobicity of the nanoparticles.     

Metallic cation induced one-dimensional assembly of poly(acrylic acid)-1-dodecanethiol-stabilized gold nanoparticles

In this work, we report a simple approach for controllable synthesis of one-dimensional (1D) gold nanoparticle (AuNP) assemblies in solution. In the presence of divalent metallic ions, poly(acrylic acid)-1-dodecanethiol-stabilized AuNPs (PAA-DDT@AuNPs) are found to form 1D assemblies in aqueous solution by an ion-templated chelation process; this causes an easily measurable change in the absorption spectrum of the particles. The assemblies are very stable and remain suspended in solution for more than one month without significant aggregation. The morphologies of these 1D assemblies are dependent on the concentration of metallic cations in the solution. While lower concentrations led to the formation of particle dimers, higher concentrations generated long nanoparticle chain networks. In addition, the effect of EDTA, the solution pH, and the size of the PAA-DDT@AuNPs is also studied for further exploration of the mechanism of the formation of the 1D assemblies.     

Symmetric and asymmetric adsorption of pH-responsive gold nanoparticles onto microgel particles and dispersion characterisation

The interaction between carboxylic acid-stabilised gold nanoparticles (AuNP) and pH-responsive microgels is shown. The microgel particles are a copolymer of N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA) and N-isopropylacrylamide (NIPAM). The microgel properties are presented by their hydrodynamic diameter and electrophoretic mobility in response to pH. These microgel particles are pH-responsive under neutral conditions decreasing in diameter beyond pH 7. The dispersion characteristics of AuNP adsorbed onto the microgel network are shown with respect to adsorbed amount and the pH-responsive properties of the AuNP. This data is presented between pH 3 and 6 where the microgel properties remain constant. Asymmetric adsorption of AuNP onto poly(DMAPMA-co-NIPAM) microgels is achieved by adsorption of nanoparticles, from the aqueous phase, onto microgel-stabilised oil-in-water emulsions. These asymmetrically modified microgels display very different dispersion behaviour, in response to pH, due to their dipolar nature.     

Using colloid lithography to fabricate silicon nanopillar arrays on silicon substrates

In this study, we partially grafted geminal silanol groups in the protecting organic shells on the surfaces of gold nanoparticles (AuNPs) and then assembled the alkyl-AuNP-Si(OH)(4) particles onto the surfaces of silicon (Si) wafers. The density of assembled AuNPs on the Si surface was adjusted by varying the geminal silanol group content on the AuNP surface; at its optimal content, it approached the high assembly density (0.0254 particles/nm(2)) of an AuNP assembled monolayer. Using reactive-ion etching (RIE) with the templates as masks, we transferred the patterned AuNP assemblies to form large-area, size-tunable, Si nanopillar arrays, the assembly density of which was controlled by the dimensions of the AuNPs. Using this colloidal lithography (CL) process, we could generate Si nanopillars having sub-10-nm diameters and high aspect ratios. The water contact angles of the high-aspect-ratio Si nanopillars approached 150°. We used another fabrication process, involving electron beam lithography and oxygen plasma treatment, to generate hydrophilic 200-nm-resolution line patterns on a Si surface to assemble the AuNPs into 200-nm-resolution dense lines for use as an etching mask. Subsequent CL provided a patterned Si nanopillar array having a feature size of 200 nm on the Si surface. Using this approach, it was possible to pattern sub-10-nm Si nanopillar arrays having densities as high as 0.0232 nm(-2).     

Lack of nano size effect on electrochemistry of dopamine at a gold nanoparticle modified indium tin oxide electrode

Nanometer sized materials have been shown to possess excellent chemical and electrochemical catalytic properties. In this work, a gold nanoparticle (AuNP) modified indium tin oxide (ITO) electrode was employed for investigating its electro-catalytic property. AuNP was deposited on the 3-aminopropyltriethoxysilane (APTES) modified ITO electrode by self-assembly, and was characterized by scanning electron microscopy and cyclic voltammetry. Although the electrochemical reaction of dopamine was very sluggish on the ITO/APTES electrode, it was significantly enhanced after AuNP deposition. The cyclic voltammogram exhibited apparent dependence on the surface coverage of 11 nm AuNPs, which could be rationalized by different modes of mass diffusion. Among the different sizes of AuNP investigated, the lowest anodic peak potential was observed on 11 nm AuNP. However, the potential was still about 50 mV more positive than that obtained on a bulk gold electrode of similar geometry. It is therefore concluded that there is no nanometer size effect of AuNP modified ITO on the electrochemistry of dopamine.     

Multimodal coupling of optical transitions and plasmonic oscillations in rhodamine B modified gold nanoparticles

The optical properties of a photoluminescent dye rhodamine B (RhB) interacting with gold nanoparticles (AuNP) have been investigated using plasmonic absorbance, fluorescence, and resonance elastic light scattering (RELS) spectroscopy. We have found that these interactions result in a multimodal coupling that influence optical transitions in RhB. In absorbance measurements, we have observed for the first time the coupling resulting in strong screening of RhB π-π* transitions, likely caused by a contact adsorption of RhB on a conductive surface of AuNP. The nanoparticles quench also very efficiently the RhB fluorescence. We have determined that the static quenching mechanism with a non-F?rster fluorescence resonance energy transfer (FRET) from RhB molecules to AuNP is involved. The Stern-Volmer dependence F(0)/F = f(Q) shows an upward deviation from linearity, attributed to the ultra-high quenching efficiency of AuNP leading to the new extended Stern-Volmer model. A sharp RELS peak of RhB alone (λ(max) = 566 nm) has been observed for the first time and attributed to the resonance fluorescence and enhanced scattering. This peak is completely quenched in the presence of AuNP(22nm). Our quantum mechanical calculations confirm that the distance between AuNP surface and conjugated π-electron system in RhB is well within the range of plasmonic fields extending from AuNP. The optical transition coupling to plasmonic oscillations and the efficient energy transfer due to the interactions of fluorescent dyes with nanoparticles are important for biophysical studies of life processes and applications in nanomedicine.     

纳米晶体自组装结构中非辐射能量传递过程的验证

以上转换纳米粒子NaYF₄：20% Yb,2% Er@NaYF₄（标记为UCNP）和金纳米粒子（AuNP）分别作为能量传递研究的给体和受体,研究在具有确定位置关系的组装结构中二者之间的非辐射能量传递是否存在。以UCNP和AuNP作为基本构建单元,采用气-液界面溶剂挥发法,得到了连续大面积规整排列的二维UCNP单层自组装膜。再通过层层组装得到UCNP+AuNP双层膜、UCNP+NaYF₄+AuNP三层膜。利用自行搭建的光谱成像系统对自组装结构进行了发光性质测试。对比3种膜结构的发光情况,发现UCNP+AuNP双层膜和UCNP+NaYF₄+AuNP三层膜的发光与UCNP单层膜减弱幅度相近,即在我们研究的体系中UCNP和AuNP之间不存在明显的非辐射能量传递过程。本研究提供了一种几何关系明确的组装体模型,并搭建了相应的微区发光性质测试设备,验证了在我们设计的自组装模型中并不存在UCNP与AuNP的非辐射能量传递。     

Efficient synthesis of single gold nanoparticle hybrid amphiphilic triblock copolymers and their controlled self-assembly

We report on a robust approach to the size-selective and template-free synthesis of asymmetrically functionalized ultrasmall (<4 nm) gold nanoparticles (AuNPs) stably anchored with a single amphiphilic triblock copolymer chain per NP. Directed NP self-assembly in aqueous solution can be facilely accomplished to afford organic/inorganic hybrid micelles, vesicles, rods, and large compound micelles by taking advantage of the rich microphase separation behavior of the as-synthesized AuNP hybrid amphiphilic triblock copolymers, PEO-AuNP-PS, which act as the polymer-metal-polymer analogue of conventional amphiphilic triblock copolymers. Factors affecting the size-selective fabrication and self-assembly characteristics and the time-dependent morphological evolution of NP assemblies were thoroughly explored.     

Fabrication and characterization of gold/acrylic polymer nanocomposites

We report the method of incorporation of preformed gold nanoparticles (AuNPs) into the acrylic polymer (AP) matrices and optical, TEM characterization of AuNP/AP bulk and film composite. It was shown that incorporation of dodecanethiol-covered AuNP can be enhanced in the presence of SiO₂ nanoparticles, enabling at the same time a wider range of tailoring of composite properties for optical processing.