High-throughput heterogeneous integration of diverse nanomaterials on a single chip for sensing applications.

There is a large variety of nanomaterials each with unique electronic, optical and sensing properties. However, there is currently no paradigm for integration of different nanomaterials on a single chip in a low-cost high-throughput manner. We present a high throughput integration approach based on spatially controlled dielectrophoresis executed sequentially for each nanomaterial type to realize a scalable array of individually addressable assemblies of graphene, carbon nanotubes, metal oxide nanowires and conductive polymers on a single chip. This is a first time where such a diversity of nanomaterials has been assembled on the same layer in a single chip. The resolution of assembly can range from mesoscale to microscale and is limited only by the size and spacing of the underlying electrodes on chip used for assembly. While many applications are possible, the utility of such an array is demonstrated with an example application of a chemical sensor array for detection of volatile organic compounds below parts-per-million sensitivity.

Flexible, all-organic chemiresistor for detecting chemically aggressive vapors.

Chemiresistors made of thin films of single-walled carbon nanotube (CNT) bundles on cellulosics (paper and cloth) can detect aggressive oxidizing vapors such as nitrogen dioxide and chlorine at 250 and 500 ppb, respectively, at room temperature in ambient air without the aid of a vapor concentrator. Inkjet-printed films of CNTs on 100% acid-free paper are significantly more robust than dip-coated films on plastic substrates. Performance attributes include low sensor-to-sensor variation, spontaneous signal recovery, negligible baseline drift, and the ability to bend the sensors to a crease without loss of sensor performance.

Oxidative template for conducting polymer nanoclips.

Bulk quantities of electronic conducting polymers such as polyaniline, polypyrrole, and poly(3,4-ethylenedioxythiophene), having an unusual 2D nanoclip-like morphology is described using a general oxidative template assembly route which is orchestrated by an insoluble complex formed between an anionic oxidant (S(2)O(8)(2-)) and a cationic surfactant.

Catalyst-free synthesis of oligoanilines and polyaniline nanofibers using H(2)O(2).

Nanofibers of polyaniline and oligoanilines of controlled molecular weight, e.g., tetraaniline, octaaniline, and hexadecaaniline, are synthesized using a versatile high ionic strength aqueous system that permits the use of H(2)O(2) with no added catalysts as a mild oxidizing agent. Films of oligoanilines deposited on plastic substrates show a robust and reversible chemiresistor response to NO(2) vapor at room temperature in ambient air (100-5 ppm).

Microwave synthesis of nanocarbons from conducting polymers.

Bulk quantities of nanocarbons having pre-selected morphology can be synthesized in a simple and rapid microwave heating approach directly from conducting polymers.

Flexible carbon nanotube sensors for nerve agent simulants.

Chemiresistor-based vapour sensors made from network films of single-walled carbon nanotube (SWNT) bundles on flexible plastic substrates (polyethylene terephthalate, PET) can be used to detect chemical warfare agent simulants for the nerve agents Sarin (diisopropyl methylphosphonate, DIMP) and Soman (dimethyl methylphosphonate, DMMP). Large, reproducible resistance changes (75-150%), are observed upon exposure to DIMP or DMMP vapours, and concentrations as low as 25 ppm can be detected. Robust sensor response to simulant vapours is observed even in the presence of large equilibrium concentrations of interferent vapours commonly found in battle-space environments, such as hexane, xylene and water (10 000 ppm each), suggesting that both DIMP and DMMP vapours are capable of selectively displacing other vapours from the walls of the SWNTs. Response to these interferent vapours can be effectively filtered out by using a 2 µm thick barrier film of the chemoselective polymer polyisobutylene (PIB) on the SWNT surface. These network films are composed of a 1-2 µm thick non-woven mesh of SWNT bundles (15-30 nm diameter), whose sensor response is qualitatively and quantitatively different from previous studies on individual SWNTs, or a network of individual SWNTs, suggesting that vapour sorption at interbundle sites could be playing an important role. This study also shows that the line patterning method used in device fabrication to obtain any desired pattern of films of SWNTs on flexible substrates can be used to rapidly screen simulants at high concentrations before developing more complicated sensor systems.

Absolute molecular weight of polyaniline.

The absolute molecular weight of polyaniline in the pernigraniline, emeraldine, and leucoemeraldine oxidation states has been measured by light scattering and the exact number of aniline repeat units determined for the first time. Using potential-time profiling to monitor the chemical oxidative polymerization of aniline using ammonium peroxydisulfate oxidant, all three oxidation states of polyaniline can be synthesized in one step and the evolution of polymer molecular weight monitored. The pernigraniline intermediate formed during the chemical oxidative polymerization of aniline increases by 17-20% when it is converted to emeraldine, which is consistent with a two-step polymerization mechanism. These findings establish a solid experimental framework to chemically synthesize block copolymers of polyaniline by using different monomers to intercept the reaction at the pernigraniline oxidation state.

Narrow pore-diameter polypyrrole nanotubes.

Bulk quantities of electrically conducting nanotubes of polypyrrole having narrow pore diameter (6 nm) can be synthesized rapidly by chemical oxidative polymerization of pyrrole in the presence of stoichiometric amounts of V2O5 nanofibers. The V2O5 nanofibers act as templates for polymerization and yield, as the initial product, polypyrrole nanotubes with pores filled with V2O5. The V2O5 dissolves readily in aq. 1.0 M HCl, yielding hollow polypyrrole nanotubes having conductivity of approximately 2 S/cm. As-synthesized polypyrrole nanotubes spontaneously reduce noble metal ions to the corresponding metal nanoparticles at room temperature without any capping or dispersing agents. For example, 3-5 nm size nanoparticles of Ag, Au, and Pd, etc., deposit readily on the surface of the tubes which then migrate spontaneously to the pore, and, in the case of Ag, coalesce in the core, yielding 4-8 nm diameter coaxial cables of Ag surrounded by a 20-30 nm thick polypyrrole fiber sheath.

Chemical synthesis of PEDOT nanofibers.

A one-step, room-temperature method is described to chemically synthesize bulk quantities of microns long, 100-180 nm diameter nanofibers of electrically conducting poly(3,4-ethylenedioxythiophene)(PEDOT) in the form of powders, or as optically transparent, substrate-supported films using a V2O5 seeding approach.

Bulk synthesis of polypyrrole nanofibers by a seeding approach.

The morphology of doped polypyrrole.Cl powder changes dramatically from granular to nanofibrillar when a very small amount (1-4 mg) of V2O5 nanofibers are added to a chemical oxidative polymerization of pyrrole in aq 1.0 M HCl using (NH4)2S2O8 as the oxidant. Unlike the polyaniline system, a key synthetic requirement in the polypyrrole system is for the seed template to be "active", i.e., to be capable of independently oxidizing the pyrrole monomer. Thin, strongly adherent films can be obtained on inert surfaces such as glass, plastics, etc., directly from the polymerization mixture without any bulk product isolation steps, significantly simplifying the processing of these nanofibers.

Polyaniline nanofibers: chemical synthesis using surfactants.

Nanofibers of doped polyaniline.HCSA having diameters 1-2 nm are observed in TEM images of bath sonicated aqueous dispersions of larger nanofibers (30-50 nm diameter) synthesized by surfactant-assisted chemical oxidative polymerization of aniline in dilute aqueous organic acids.

Fabrication and characterization of thin films of single-walled carbon nanotube bundles on flexible plastic substrates.

A convenient method to obtain patterns of films of single-walled carbon nanotubes (SWNT) bundles on flexible plastic is described. Using the Line Patterning method SWNT films of thickness ranging from approximately 300-1500 nm can be obtained from aqueous surfactant-supported dispersions of chemically purified SWNT bundles synthesized by the pulsed-laser ablation method. These films are strongly adherent and are competitive in performance with commercially available films of indium-tin-oxide (ITO) on plastics. For example, an approximately 1500 thick film of SWNT on poly(ethylene terephthalate) (PET) shows a surface resisitvity of approximately 80 Omega/sq, optical transparency >80%, and robust flexibility. Unlike ITO/PET, films of SWNT/PET can be folded and bent to a crease without cracking. The simple techniques involoved in obtaining these films (i.e., those without requiring lithography or ink-jet printing) could help facilitate the rapid fabrication of transparent, flexible electronic devices, heralding what promises to be a new approach towards the development of next-generation optoelectronic devices.

Synthesis of polyaniline nanofibers by "nanofiber seeding".

Seeding a conventional chemical oxidative polymerization of aniline with even very small amounts of biological, inorganic, or organic nanofibers (usually <1%) dramatically changes the morphology of the resulting doped electronic polymer polyaniline from nonfibrillar (particulate) to almost exclusively nanofibers. The nanoscale morphology of the original seed template is transcribed almost quantitatively to the bulk precipitate. These findings could have immediate impact in the design and development of high-surface area electronic materials.