Synthesis of organic-metal hybrid nanowires by cooperative self-organization of tetrathiafulvalene and metallic gold via charge-transfer

Formation of Single Micro- and Nanowires with Extreme Aspect Ratios in Microfluidic Channels

Shown here is the site-specific formation of single extraordinarily long metal-organic micro- and nanowires using a microfluidic device made of poly(dimethylsiloxane) (PDMS). This approach exploits two concepts, i) the diffusion of organic precursor molecules through PDMS and ii) the use of microfluidic channels as a growth template. To initiate wire formation, metal and organic precursor solutions are filled into different supply channels that are separated by PDMS. As the precursor diffuses through PDMS, and thereby infiltrates the adjacent channel, the growth of micro- and nanowires starts at the side walls of this adjacent channel. The formation yields single wires with sizes ranging from several hundreds of micrometers to millimeters at diameters of 0.5-2 µm. The principles of this formation pathway are demonstrated with the reaction of tetrathiafulvalene (TTF) and gold(III) ions that yields Au-TTF wires. The influence of various reaction parameters including the choice of solvents and the chip fabrication protocol on the reaction are evaluated. Based on these findings, a further microfluidic device design with orthogonally arranged channels is developed, and the formation of single wires in a channel-defined pattern is demonstrated. Moreover, the possibility of pulsed precursor supply allows for advanced control over the growth of the wires.

Gold Raspberry-Like Colloidosomes Prepared at the Water-Nitromethane Interface

In this study, we propose a simple shake-flask method to produce micron-size colloidosomes from a liquid-liquid interface functionalized with a gold nanoparticle (AuNP) film. A step-by-step extraction process of an organic phase partially miscible with water led to the formation of raspberry-like structures covered and protected by a gold nanofilm. The distinctive feature of the prepared colloidosomes is a very thin shell consisting of small AuNPs of 12 or 38 nm in diameter instead of several hundred nanometers reported previously. The interesting and remarkable property of the proposed approach is their reversibility: the colloidosomes may be easily transformed back to a nanofilm state simply by adding pure organic solvent. The obtained colloidosomes have a broadband absorbance spectrum, which makes them of great interest in applications such as photothermal therapy, surface-enhanced Raman spectroscopy studies, and microreactor vesicles for interfacial electrocatalysis.

Self-assembly and redox induced phase transfer of gold nanoparticles at a water–propylene carbonate interface

Citrate-stabilized gold nanoparticles were found to spontaneously self-assemble into a lustrous film at a bare water–propylene carbonate interface after vigorous shaking, due to the extremely low interfacial tension. The presence of the electron donor, tetrathiafulvalene, in the oil phase, led to the extraction of particles into the organic phase.

Shape-controlled synthesis of hybrid nanomaterials via three-dimensional hydrodynamic focusing

Shape-controlled synthesis of nanomaterials through a simple, continuous, and low-cost method is essential to nanomaterials research toward practical applications. Hydrodynamic focusing, with its advantages of simplicity, low-cost, and precise control over reaction conditions, has been used for nanomaterial synthesis. While most studies have focused on improving the uniformity and size control, few have addressed the potential of tuning the shape of the synthesized nanomaterials. Here we demonstrate a facile method to synthesize hybrid materials by three-dimensional hydrodynamic focusing (3D-HF). While keeping the flow rates of the reagents constant and changing only the flow rate of the buffer solution, the molar ratio of two reactants (i.e., tetrathiafulvalene (TTF) and HAuCl4) within the reaction zone varies. The synthesized TTF-Au hybrid materials possess very different and predictable morphologies. The reaction conditions at different buffer flow rates are studied through computational simulation, and the formation mechanisms of different structures are discussed. This simple one-step method to achieve continuous shape-tunable synthesis highlights the potential of 3D-HF in nanomaterials research.

Confined synthesis and integration of functional materials in sub-nanoliter volumes

We present a novel microchip-based approach to combine the synthesis, characterization, and utilization of different functional materials on a single platform. A two-layer microfluidic device comprising 10 parallel actuated reaction chambers with volumes of a few hundred picoliters is used to localize and confine the synthesis, while the surfaces of the reaction chambers comprise an electrode array for direct integration and further characterization of the created crystalline assemblies without the need for further manipulation or positioning devices. First we visualized and evaluated the dynamics of our method by monitoring the formation of a fluorescent metal-organic complex (Zn(bix)). Next, we induced the site-specific growth of two types of organic conductive crystals, AuTTF and AgTCNQ, directly onto the electrode arrays in one- and two-step reactions, respectively. The performance of the created AgTCNQ crystals as memory elements was thoroughly examined. Moreover, we proved for first time that AuTTF composites can be used as label-free sensing elements.

Preparation and characterization of conducting mixed-valence 9,9'-dimethyl-3,3'-bicarbazyl rectangular nanowires

The facile synthesis of an organic electric conducting nanowire is described. The simple oxidation of 9-methylcarbazole by iron(III) perchlorate in a methanol/acetonitrile mixture under atmospheric pressure and temperature produces abundant nanowires without using a template. The nanowire consists of 9,9'-dimethyl-3,3'-dicarbazyl and has a rectangular nanowire shape with an average diameter of 397 ± 50 nm and length of 17 ± 5 μm. The results of the elemental analysis, (1)H NMR, FT-IR, XPS, and ESR measurements revealed that the chemical composition of the nanowire is (dicarbazyl)(0.12)(dicarbazylium·ClO(4)(-))(0.88)·H(2)O. This result, combined with the UV-vis-NIR measurement, demonstrates that 9,9'-dimethyl-3,3'-dicarbazyl stacks in a mixed valence state. The nanowire is electroactive and has an electric conductivity of 3.0 × 10(-5) S cm(-1).

Guided assembly of metal and hybrid conductive probes using floating potential dielectrophoresis

We present the site-selective, parallel and reproducible formation of conductive gold and tetrathiafulvalene-gold (TTF-Au) hybrid micro- and nanowires from their respective ion salt and cation-radical solutions. While the formation of micro- and nanowires by means of dielectrophoresis with directly coupled electrodes has been thoroughly investigated in recent studies, we present here the first relevant example of metal and hybrid wire assembly obtained by floating potential dielectrophoresis. In this configuration, the assembly of micro- and nanowires is achieved by capacitively coupling a large electrode (bias electrode) to a conductive substrate (p-doped Si) separated by an insulating oxide layer. In contrast to former studies, this allows parallel production of micro- and nanowires with only one pair of electrodes connected to a sine wave generator. We further demonstrate that these structures are suitable probes for localized surface enhanced Raman spectroscopy (SERS).

Controlling the length and location of in situ formed nanowires by means of microfluidic tools

Progress in microelectronics, sensors and optics is strongly dependent on the miniaturization of components, and the integration of nanoscale structures into applicable systems. In this regard, conventional top-down technologies such as lithography have limits concerning the dimensions and the choice of material. Therefore, several bottom-up approaches have been investigated to satisfy the need for structures with large aspect ratios in the nanometre regime. For further implementation, however, it is crucial to find methods to define position, orientation and length of the nanowires. In this study, we present a microchip to trap in situ formed bundles of nanowires in microsized cages and clamps, thereby enabling immobilisation, positioning and cutting-out of desired lengths. The microchip consists of two layers, one of which enables the formation of metal-organic nanowires at the interface of two co-flowing laminar streams. The other layer, separated by a thin and deflectable PDMS membrane, serves as the pneumatic control layer to impress microsized features ("donuts") onto the nanowires. In this way, a piece of the nanowire bundle with a prescribed length is immobilised inside the donut. Furthermore, partly open ring-shaped structures enabled trapping of hybrid wires and subsequent functionalisation with fluorescent beads. We believe that the method is a versatile approach to form and modify nanoscale structures via microscale tools, thereby enabling the construction of fully functional nanowire-based systems.

Facile preparation of concentration-gradient materials with radical spin of the mixed-valence tetrathiafulvalene in conventional polymer films

We describe here the facile methods for the stepwise regulation of the formation of tetrathiafulvalene (TTF) radical cation and the self-assembly to the mixed-valence state of TTF in various polymer films. The homogeneous polymer composites containing TTF and (1R)-3,3-dimethylbicyclo[2.2.1]hepta-2-one-1-triflate as a photoinduced acid generator in several kinds of conventional polymers were prepared, and the phototriggered conversion of TTF to radical cation via protonation in the films was executed. The amount of the TTF radical species can be controlled by the length of UV-irradiation time to the polymer composite films. In addition, the formation of the mixed-valence TTF can be observed in the composite films by annealing after UV irradiation when the glass transition temperature of the matrices was sufficiently higher than the reaction temperature during the photoirradiation. Finally, we presented the facile patterning method for preparing the composite with the concentration gradient of TTF radical and the mixed-valence TTF.

Photoinduced radical generation and self-assembly of tetrathiafulvalene into the mixed-valence state in the poly(vinyl chloride) film under UV irradiation

The photoinduced self-assembly and the formation of the mixed-valence state of tetrathiafulvalene (TTF) in the solid state are reported. The polymer composites containing TTF in poly(vinyl chloride) (PVC) were prepared, and oxidation of TTF by chlorine radical generated by UV irradiation in PVC was investigated. The formation of the mixed-valence state of TTF in the composite films by UV irradiation was observed, and the resulting TTF radical species, including the mixed-valence state after the photopatterning, exhibited extremely high stability in the composite films. Finally, we performed the fabrication of the gradient materials of the radical concentrations on the TTF/PVC composites with the photopatterning.