Templated assembly of gold nanoparticles into microscale tubules and their application in surface-enhanced Raman scattering

We report a simple procedure to assemble gold nanoparticles into hollow tubular morphology with micrometer scale, wherein the citrate molecule is used not only as a reducing and capping agent, but also as an assembling template. The nanostructure and growth mechanism of microtubes are explored via SEM, TEM, FTIR spectra, and UV-vis spectra studies. The incorporation of larger gold nanoparticles by electroless plating results in an increase in the diameter of microtubes from 900 nm to about 1.2 microm. The application of the microtubes before and after electroless plating in surface-enhanced Raman scattering (SERS) is investigated by using 4-aminothiophenol (4-ATP) as probe molecules. The results indicate that the microtubes both before and after electroless plating can be used as SERS substrates. The microtubes after electroless plating exhibit excellent enhancement ability.     

Sulfate anion templation of a neutral pseudorotaxane assembly using an indolocarbazole threading component

The first example of anion templated pseudorotaxane formation between two neutral components in solution and in surface assembled monolayers is described.     

pH-Controlled assembly and disassembly of a cryptand/paraquat [2]pseudorotaxane

Strong complexation between a pyridine-containing cryptand and paraquat can be reversibly switched off (and back on) by adding acid (and then base).     

Copper(I) pseudorotaxane monolayers assembled on gold electrodes

Two new copper (I) pseudorotaxanes bearing a thioctic acid appended unit have been prepared and deposited onto a gold electrode surface, leading to surface-attached electroactive pseudorotaxanes.     

Growth of poly(pseudorotaxane) on gold using host-stabilized charge-transfer interaction

A novel supramolecular polymer (poly(pseudorotaxane)) in which the repeating units are linked by host-stabilized charge-transfer interaction between the guest molecules is grown on gold and characterized.     

Coordination-driven assembly of molecular rectangles via an organometallic "clip"

The combination of linear dipyridyl ligands with a new type of modular building unit, based upon a 1,8-platinum-functionalized anthracene, leads to the self-organization of rectangular frameworks. X-ray crystallography confirms the cyclic structure of the supramolecular cationic complexes. Spectral assignments were provided by 2D NOESY (1)H NMR experiments.     

Dithiocarbamate assembly on gold

Au surfaces are functionalized by stable dithiocarbamate ligands when exposed to carbon disulfide and secondary amines. The adsorbed dithiocarbamates are robust under a wide pH range and can resist displacement by other chemisorptive surfactants, providing an attractive method for conjugating sensitive molecules onto metal surfaces.     

pH-triggered assembly of gold nanorods

The self-assembly of surfactant-protected gold nanorods (aspect ratio 3.3 +/- 0.3, 20.6 +/- 5.5 nm width, and 67.5 +/- 9.0 nm length) into ordered structures using adipic acid is presented. As made, the gold nanorods are coated with cationic surfactant, which gives them a net positive charge in aqueous solution. The pH-dependent assembly is directed by electrostatic interactions between the positively charged nanorods and negatively charged, deprotonated adipic acid. Absorption spectra and light scattering measurements of these nanorods suggest that aggregation is initiated in solution in the presence of adipic acid at pH 7-8, but not at pH 3, to form small assemblies of nanorods. Zeta potential measurements show that the assembly is significantly less positively charged in the presence of deprotonated adipic acid than when adipic acid is fully protonated.     

Directed assembly of gold nanoparticles

As a complement to common “top–down” lithography techniques, “bottom–up” assembly techniques are emerging as promising tools to build nanoscale structures in a predictable way. Gold nanoparticles that are stable and relatively easy to synthesize are important building blocks in many such structures due to their useful optical and electronic properties. Programmed assembly of gold nanoparticles in one, two, and three dimensions is therefore of large interest. This review focuses on the progress from the last three years in the field of directed gold nanoparticle and nanorod assembly using, for example, DNA or specific chemical interactions as template.     

Lipid bilayer assembly at a gold nanocavity array

The assembly of lipid bilayer membranes, using ultrasonic disruption of liposomes of L-α-Dimyristoyl phosphatidylcholine, across 820 nm diameter spherical cap gold cavity arrays is demonstrated.     

pH-Switched fluorescent pseudorotaxane assembly of cucurbit[7]uril with bispyridinium ethylene derivatives

¹H NMR spectra and fluorescence analysis revealed that the molecular shuttle and pseudorotaxane assembly of Q[7] with guest G²⁺ can be significantly switched via protonation and deprotonation of the terminal carboxylates of the guest.     

Templated assembly of polymer particles into mesoscopic clusters with well-defined configurations

We report on the fabrication of colloidal clusters through the combination of spherical particles. Polystyrene latex particles bearing amino groups on their surface were used as building blocks of the clusters. Packing of these particles with diameters of 91 and 154 nm into assemblies with defined configurations was accomplished using narrow dispersed emulsion droplets as templates. The building blocks of the clusters adhered to the oil–water interphase due to the Pickering effect. Subsequent evaporation of the dispersed phase forced them to pack into small clusters. Addition of the particles via the dispersed phase led to higher yields of clusters than if the building blocks were added via the continuous phase. All clusters had well-defined configurations. Because the dimensions of these clusters were below 400 nm, the colloidal assemblies underlay Brownian motion, which resulted in stable suspensions. The number and yields of different species could be controlled via the concentration of the building blocks and surfactant within the emulsions. Moreover, the nature of the dispersed phase itself had a strong impact on the cluster formation. When cyclohexane was used as the dispersed phase, predominately, particle doublets and triplets were obtained. The use of toluene-in-water emulsions resulted into a broader spectrum of clusters of up to 12 constituents. Such clusters could satisfy the demand for particles with complex but defined shapes and special symmetries for the fabrication of novel hierarchically organized materials.     

Templated synthesis and assembly with sustainable cellulose nanomaterial for functional nanostructure

Cellulose - Templated synthesis and assembly for nanostructured materials with tailored properties have received considerable attention. The powerful templates with predefined structures can guide...     

Templated assembly of sulfide nanoclusters into cubic-C3N4 type framework

Here we report a new type of nanocluster superlattice in which each four-connected cluster ([M4In16S31],6- M = Fe, Co, Zn, and Cd) alternates with a three-connected sulfur anion (S2-) to form a rare and yet theoretically important non-centrosymmetric and non-interpenetrating (3,4)-connected net topologically identical to that of the hypothetical cubic carbon nitride type net. These materials have a ring size consisting of 16 tetrahedral atoms. Because of the large cluster size and the elimination of structural intergrowth, the volume fraction of the inorganic framework is as low as 38%. A strong photoluminescent emission has also been observed.     

Template-free parallel one-dimensional assembly of gold nanoparticles

In this work, we have identified key process parameters to generate parallel unidirectional 1D assemblies of gold nanoparticles with the assistance of organic surfactants. By controlling the surfactant population, metal particle size, and amount of solvent for dispersion, the length of nanoparticle chains and their interchain space can be further tailored. In principle, the general findings of this work can also be extended to large-scale 1D organization of other transition/noble metal nanoparticles using simple organic surfactants.     

Homocysteine-mediated reactivity and assembly of gold nanoparticles

This paper reports the findings of an investigation of the reactivity and assembly of gold nanoparticles mediated by homocysteine (Hcys), a thiol-containing amino acid found in plasma. The aim is to gain insight into the interparticle interaction and reactivity, which has potential application for the detection of thiol-containing amino acids. By monitoring the evolution of the surface plasmon resonance absorption and the dynamic light scattering of gold nanoparticles in the presence of Hcys, the assembly was shown to be dependent on the nature and concentration of the electrolytes, reflecting an effective screening of the diffuse layer around the initial citrate-capped nanoparticles that decreases the barrier to the Hcys adsorption onto the surface, and around the subsequent Hcys-capped nanoparticles that facilitate the zwitterion-type electrostatic interactions between amino acid groups of Hcys bound to different nanoparticles. A key element of the finding is that the interparticle zwitterion interaction of the Hcys-Au system is much stronger than the expectation for a simple Hcys or Au solution, a new phenomenon originating from the unique nanoscale interparticle interaction. The strength and reversibility of the interparticle zwitterion-type electrostatic interactions between amino acid groups are evidenced by the slow disassembly upon increasing pH at ambient temperatures and its acceleration at elevated temperature. These findings provide new insight into the precise control of interfacial interactions and reactivities between amino acids anchored to nanoparticles and have broad implications in the development of colorimetric nanoprobes for amino acids.     

pH-controlled reversible assembly of peptide-functionalized gold nanoparticles

The assembly/disassembly process of carboxylated peptide-functionalized gold nanoparticles (peptide-GNPs) was studied within the pH interval of 2.5 to 10. The assembly process was not well controlled at pH 2.5, leading to the formation of 3D structures of GNPs, whereas at pH 4 we observed controlled assembly with the formation of only a network of 1D chains. In the pH range of 2.5 to 4, the assembly proceeded with the formation of a combination of two extremes (i.e., having both 1D and 2D nanostructures). The assembly process was reversed on changing the pH of the medium to 10. The assembly/disassembly process was monitored using UV-vis spectroscopy and finally confirmed by TEM analysis. This assembly resulted from the intermolecular H-bonding between two carboxylic acid groups of peptides bound to the two adjacent GNPs and were confirmed by FTIR spectroscopy.     

Novel spherical assembly of gold nanoparticles mediated by a tetradentate thioether

The ability to construct three- and two-dimensional architectures via nanoscale engineering is important for emerging applications of nanotechnology in sensors, catalysis, controlled drug delivery, microelectronics, and medical diagnostics. In this paper, we report novel 3D assembly using multidentate molecular building blocks. It is demonstrated that the interparticle linking of gold nanoparticles (3.7 nm core size) by a tetradentate thioether, tetra[(methylthio)methyl]silane, leads to the formation of a spherical assembly. The spherical size (30-80 nm diameter) is dependent on reaction time and relative ratio of the building blocks. The novelty of this approach is the viability of multidentate thioethers to link nanoparticles and produce spherical assemblies that can be readily assembled and disassembled. The spherical assembly can also be partially "melted" depending on the nature of interfacial interactions between the assembly and the substrate. These unusual morphological properties in shape and surface interaction and the intriguing assembling-disassembling capabilities may form the basis of designing and fabricating novel functional nanostructures.