Daniela Iacopino

Probing intrinsic transport properties of single metal nanowires: Direct-write contact formation using a focused ion beam

The transport characteristics of 70-nm-diameter platinum nanowires (NWs), fabricated using a pore-templated electrodeposition process and individually contacted using a focused ion beam (FIB) method, are reported. This approach yields nanowire devices with low contact resistances (∼400Ω) and linear current–voltage characteristics for current densities up to 65kA∕cm2. The intrinsic nanowire resistivity (33±5μΩcm) indicates significant contributions from surface- and grain-boundary scattering mechanisms. Fits to the temperature dependence of the intrinsic NW resistance confirm that grain-boundary scattering dominates surface scattering (by more than a factor of 2) at all temperatures. Our results demonstrate that FIB presents a rapid and flexible method for the formation of low-resistance ohmic contacts to individual metal nanowires, allowing intrinsic nanowire transport properties to be probed.

Ion-Transfer Electrochemistry at Arrays of Nanointerfaces between Immiscible Electrolyte Solutions Confined within Silicon Nitride Nanopore Membranes

Ion transfer across interfaces between immiscible liquids provides a means for the nonredox electrochemical detection of ions. Miniaturization of such interfaces brings the benefits of enhanced mass transport. Here, the electrochemical behavior of geometrically regular arrays of nanoscale interfaces between two immiscible electrolyte solutions (nanoITIES arrays) is presented. These were prepared by supporting the two electrolyte phases within silicon nitride membranes containing engineered arrays of nanopores. The nanoITIES arrays were characterized by cyclic voltammetry of the interfacial transfer of tetraethylammonium cation (TEA(+)) between the aqueous phase and the gelled organic phase. Effects of pore radius, pore center-to-center separation, and number of pores in the array were examined. The ion transfer produced apparent steady-state voltammetry on the forward and reverse sweeps at all experimentally accessible scan rates and at all nanopore array designs. However, background-subtraction of the voltammograms revealed the evolution of a peak-shaped response on the reverse sweep with increasing scan rate, indicative of pores filled with the organic phase to a certain extent. The steady-state voltammetric behavior at the nanoITIES arrays on the forward sweep for arrays with significant diffusion zone overlap between adjacent nanoITIES is indicative of the dominance of radial diffusion to interfaces at the edge of the arrays over linear diffusion to interfaces within the arrays. This implies that nanoITIES arrays, which occupy an overall area of micrometer dimensions, behave like a single microITIES of corresponding area to the nanoITIES array.

Dielectrophoretic self-assembly of polarized light emitting poly(9,9-dioctylfluorene) nanofibre arrays

Conjugated polymer based 1D nanostructures are attractive building blocks for future opto-electronic nanoscale devices and systems. However, a critical challenge remains the lack of manipulation methods that enable controlled and reliable positioning and orientation of organic nanostructures in a fast, reliable and scalable manner. To address this challenge, we explore dielectrophoretic assembly of discrete poly(9,9-dioctylfluorene) nanofibres and demonstrate site selective assembly and orientation of these fibres. Nanofibre arrays were assembled preferentially at receptor electrode edges, being aligned parallel to the applied electric field with a high order parameter fit (∼ 0.9) and exhibiting an emission dichroic ratio of ∼ 4.0. As such, the dielectrophoretic method represents a fast, reliable and scalable self-assembly approach for manipulation of 1D organic nanostructures. The ability to fabricate nanofibre arrays in this manner could be potentially important for exploration and development of future nanoscale opto-electronic devices and systems.

Interfacial charge transfer dynamics in CdSe/dipole molecules coated quantum dot polymer blends

We report our results on the influence of the dipole moment of small molecules anchored to the surface of CdSe nanocrystals, over the interfacial charge recombination dynamics in CdSe/P3HT (P3HT : poly-3-hexylthiophene). The polarizability of the CdSe/P3HT interface is key to achieving efficient charge separation and slow back electron transfer, two of the most important processes to boost the photocurrent and voltage in CdSe/P3HT photovoltaic devices.

Imaging the DNA and nanoparticle components of a self-assembled nanoscale architecture

We describe the self-assembly in solution of a nanoscale architecture from DNA and gold nanoparticles. Also described is the characterization of this nanoscale architecture by transmission electron microscopy, atomic force microscopy and near-field scanning optical microscopy. A key finding is that it is possible to image both the DNA and nanoparticle components of the nanoscale architecture.

Synthesis of Oligonucleotides Carrying Anchoring Groups and Their Use in the Preparation of Oligonucleotide–Gold Conjugates

Oligodeoxynucleotide conjugates 1–15 carrying anchoring groups such as amino, thiol, pyrrole, and carboxy groups were prepared. A post-synthetic modification protocol was developed. In this method 2′-deoxy-O4-(p-nitrophenyl)uridine-3-phosphoramidite was prepared and incorporated in oligonucleotides. After assembly, the modified nucleoside was made to react with different amines carrying the anchoring groups. At the same time, protecting groups were removed to yield the desired oligonucleotide conjugates. In a second approach, amino, thiol, and carboxylic groups were introduced into the 3′-end of the oligonucleotides by preparing solid supports loaded with the appropriate amino acids. Oligonucleotidegold conjugates were prepared and their binding properties were examined.

Polythiophene mesowires: synthesis by template wetting and local electrical characterisation of single wires

We report on the synthesis of semiconducting mesowires from regioregular poly(3-hexylthiophene) via melt injection into a porous alumina template. Following liberation from the template, mesowires with diameters ∼450 nm and average lengths of 10 µm were obtained. For two-terminal electrical contacting of individual mesowires on insulating substrates, the drain electrode was formed by shadow masking and metal evaporation, and a conducting probe atomic force microscope tip was employed as the source electrode. This approach enabled combined topographic imaging and spatially resolved electrical characterisation of individual mesowires, allowing the intrinsic mesowire resistivity (700 ± 300 Ω m) as well as the contact resistance (10 ± 6 GΩ) to be estimated. Fitting the measured data to a thermionic emission–diffusion model yielded a hole mobility ∼2 × 10−5 cm2 V−1 s−1 and a metal–polymer interface barrier height ∼0.1 eV.

Metal nanoparticle–semiconductor nanowire hybrid nanostructures for plasmon-enhanced optoelectronics and sensing

Plasmonic metal nanoparticles have recently attracted increasing interest due to their nanosized dimensions, tunable optical properties in the visible and near-infrared regions of the spectrum and easy manufacturing. Although the optical properties of these sub-wavelength objects arising from plasmonic resonances have been extensively investigated in both isolated and assembled structures, their rational integration in 1D semiconductor-based devices for generation of engineered properties is a novel and vastly unexplored field. In particular, development of metal nanoparticle–1D semiconductor hybrid nanostructures has been hampered by a number of challenges including limited control of component assembly processes and modest theoretical and experimental understanding of fundamental physical phenomena occurring in such hybrids. In this feature article, we describe recent progress in fabrication methods and review the relevant plasmonic properties of metal nanoparticles that can be exploited to manipulate, enhance and optimize the performance of semiconductor nanowire-based devices. Finally, we explore the enhanced properties of hybrid metal nanoparticle–semiconductor nanowire structures and describe their application in optoelectronics and sensing.

Facile Formation of Ordered Vertical Arrays by Droplet Evaporation of Au Nanorod Organic Solutions

Droplet evaporation is a simple method to induce organization of Au nanorods into ordered superstructures. In general, the self-assembly process occurs by evaporation of aqueous suspensions under strictly controlled experimental conditions. Here we present formation of large area ordered vertical arrays by droplet evaporation of Au nanorod organic suspensions. The uncontrolled (free air) evaporation of such suspensions yielded to formation of ordered nanorod domains covering the entire area of a 5 mm diameter droplet. Detailed investigation of the process revealed that nanorods organized into highly ordered vertical domains at the interface between solvent and air on a fast time scale (minutes). The self-assembly process mainly depended on the initial concentration of nanorod solution and required minimal control of other experimental parameters. Nanorod arrays displayed distinct optical properties which were analyzed by optical imaging and spectroscopy and compared to results obtained from theoretical calculations. The potential use of synthesized arrays as surface-enhanced Raman scattering probes was demonstrated with the model molecule 4-aminobenzenthiol.

Enhanced thermal and ultrasonic stability of a fungal protease encapsulated within biomimetically generated silicate nanospheres.

BACKGROUND Dendrimers are highly branched synthetic macromolecules with a globular shape. They have been successfully used for generation of nanospheres at mild conditions via biomimetic silicification. Encapsulation of enzyme molecules within these nanospheres during their synthesis is a promising method for rapid and efficient entrapment of several enzymes. However, encapsulation of proteolytic enzymes has been rarely done via biomimetic silicification. As well, the operational stability of encapsulated enzyme has not been systematically reported. METHODS A proteolytic enzyme, either alpha-Chymotrypsin or a fungal protease from Aspergilus Oryzea was encapsulated along with iron oxide nanoparticles within particles yielded via biomimetic silicification of different generations of polyamidoamine (PAMAM) dendrimers. Stability of encapsulated enzyme was compared to that of free enzyme during storage at room temperature. As well, their thermal and ultrasonic stabilities were measured. Scanning electron microscopy, transmission electron microscopy and optical microscopy were used to investigate the morphology of nanospheres. RESULTS Determination of encapsulation efficiency revealed that approximately 85% of fungal protease with concentration 1.4mg mL(-1) stock solution was immobilized within particles yielded by generation 0. Based on microscopic images the generated particles interconnected with each other and had spherical morphologies independent of generation. Kinetic analysis of encapsulated fungal protease demonstrated that Mechaelis-Menten constant (K(m)) slightly increased. CONCLUSION PAMAM dendrimer generation 0 could be effectively used for rapid encapsulation of a fungal protease from Aspegilus Oryzae. GENERAL SIGNIFICANCE Encapsulation significantly enhances the thermal and ultrasonic stabilities of enzymes, suggesting a range of diverse applications for them.