New research reported this week has now established an industrially relevant process for assembling carbon nanotubes that allows them to efficiently be made into fibers, coatings and films - the basic forms of material that can be used in engineering applications. The most common of processing nanotubes into neat fibers - apart from 'dry' methods where they are spun directly into ropes and yarns - are 'wet' methods where CNTs are dispersed into a liquid and solution-spun into fiber. Currently, these processes yield fibers whose properties are not sufficiently close to optimal. Successful carbon nanotube assembly begins with control of dispersion and phase behavior and requires a scientific understanding of flow, colloidal interactions and solvent removal.
Due to their unique structural and electrical properties, carbon nanotubes have been extensively investigated as promising catalyst supports to improve the efficiency of direct ethanol/methanol fuel cells. CNTs have a significantly higher electronic conductivity and an extremely higher specific surface area in comparison with the most widely-used Vulcan XC-72R carbon support. Several approaches, such as electrochemical reduction, electroless deposition, spontaneous reduction, sonochemical technique, microwave-heated polyol process, and nanoparticle decoration on chemically oxidized nanotube sidewalls, have been reported to form CNT-supported platinum catalysts. Some remarkable progress has been made in synthesis techniques; however, pioneering breakthroughs have not been made yet in terms of cost-effectiveness catalyst activity, durability, and chemical-electrochemical stability. Nanotechnology researchers in the U.S. have now discovered that platinum nanoparticles selectively grow on carbon nanotubes in accordance with single-stranded DNA locations.
Researchers have developed a self-sensing nanotechnology composite material for traffic monitoring by using piezoresistive multi-walled carbon nanotubes as an admixture. In experiments, they studied the response of the piezoresistive properties of this composite to compressive stress and they investigated with vehicular loading experiments the feasibility of using self-sensing CNT/cement composite for traffic monitoring. This nanocomposite cement has great potential for traffic monitoring use such as in vehicle detection, weigh-in-motion measurement and vehicle speed detection. An interesting aspect of this work is that, from the eventual traffic application's point of view, the pavement itself would become the traffic detection, thus eliminating the need for separate traffic flow detection sensors.
In their effort to develop a fast, sensitive, selective, inexpensive, and easy-to-use method for detecting and quantifying pathogenic bacterial cells, researchers in Spain have now demonstrated a carbon nanotube based potentiometric biosensor for selectively detecting one single colony-forming unit of the bacterium Salmonella Typhi in close to real time. The most important strength of this biosensor is that simple positive/negative tests can be carried out in real zero-tolerance conditions and without cross reaction with other types of bacteria. The ease with which measurements are taken in potentiometric analysis opens the door to greater simplicity in microbiological analysis.
To what degree nanoparticles are uptaken by plants and what their effect is on plant development is an important issue in determining the environmental impact of nanomaterials. Previously we have covered several research projects that have begun to explore nanotechnology's impact on major food crops and some of them have demonstrated quite a negative impact. But some research results also show a possible positive effect, like a recent study that demonstrates that carbon nanotubes (CNTs) can dramatically accelerate the germination and growth of tomato seeds. Work like this contributes to an important body of interdisciplinary research where nanotechnology, plant biology and biotechnology converge to open new perspectives for solving some of the important challenges of our times such as increased food and biofuel production.
The degree of mobility of a semiconductor, i.e. how well it conducts, is crucial to the effectiveness of nanoelectronic devices. Mobility determines the carrier velocity, and hence switching speed, in FETs. Researchers have determined that the theoretical mobility of an individual single-walled carbon nanotube is about 1000 times higher than any other known semiconductor. However, practical applications would require massive manufacturing of large scale nanoelectronic devices. Despite progress being made with integrating individual nanotubes in lab environments, many of today's nanomanufacturing techniques for nanoelectronic devices rely on the use of 'carbon nanotube network films' comprised of multiple carbon nanotubes. The major problem here is that the electronic properties of CNT network films are usually very poor. Researchers in South Korea have now developed a powerful strategy to solve these fundamental problems simply by controlling the connectivity of nanotube/nanowire networks.
The fundamental issue of large-scale carbon nanotube (CNT) device fabrication remains the biggest challenge for effective commercialization of CNT-based nanoelectronic devices. For CNT electronics to become a reality requires manufacturing techniques to simultaneously and reproducibly fabricate a very large number of such devices on a single chip, each accessible individually for electronic transport. Conventional nanotube growth and device fabrication techniques using chemical vapor deposition or spin-casting are unable to achieve this, due to a lack of precise control over nanotube positioning and orientation. New work conducted at Tel Aviv University utilizes the CVD growth of CNTs over pillar-patterned silicon substrates to facilitate the formation of devices with taut and aligned CNTs grown exclusively at desired positions with built-in electrical contacts.
Carbon nanotubes, like the nervous cells of our brain, are excellent electrical signal conductors and can form intimate mechanical contacts with cellular membranes, thereby establishing a functional link to neuronal structures. There is a growing body of research on using nanomaterials in neural engineering. Most studies simply grow carbon nanotubes over microelectrodes to interface with neurons extracellularly. Such an extracellular interface is non-invasive, but it only allows the action potential of neurons to be recorded. In contrast, an intracellular interface allows all of the sophisticated neural activity to be probed, but it is an invasive approach that usually destroys the neuron. Now, new research by scientists in Taiwan is the first to explore the feasibility of using CNTs to probe neural activity intracellularly, opening the way for intracellular neural probes that minimize damage to the neuron.