Carbon Nanotubes in Neuroscience
Carbon nanotubes have electrical, mechanical and chemical properties that make them one of the most promising materials for applications in neuroscience. Single-walled and multi-walled carbon nanotubes have been increasingly used as scaffolds for neuronal
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Abstract Carbon nanotubes have electrical, mechanical and chemical properties that make them one of the most promising materials for applications in neuroscience. Single-walled and multi-walled carbon nanotubes have been increasingly used as scaffolds for neuronal growth and more recently for neural stem cell growth and differentiation. They are also used in interfaces with neurons, where they can detect neuronal electrical activity and also deliver electrical stimulation to these cells. The emerging picture is that carbon nanotubes do not have obvious adverse effects on mammalian health. Thus in the near future they could be used in brain–machine interfaces. Keywords Carbon nanotubes • modification • substrates/ scaffolds • electrical interface • neurobiology
Introduction The first evidence of nano-sized carbon tubes (Fig. 1a) is thought to have been shown by Radushkevich and Lukyanovich in 1952 (1). Several other groups observed similar carbon structures afterwards but it was the efforts of two groups in 1993 (2,3) that stirred the current interest in carbon nanotubes (reviewed in (4)). Carbon nanotubes (CNTs) are composed of sheets of graphene formed into a cylinder, either a single cylinder, singlewalled carbon nanotube (SWNT) or multiple concentric cylinders, multi-walled carbon nanotube (MWNT). Doublewalled CNTs (DWNTs) are composed of two concentric graphene cylinders, and they represent an intermediate structure between MWNTs and SWNTs. The size of CNTs typically ranges from 0.4 to 2 nm in diameter for SWNTs and 2 to 100 V. Parpura (*) Department of Neurobiology Center for Glial Biology in Medicine, Atomic Force Microscopy and Nanotechnology Laboratories, Civitan International Research Center, Evelyn F. McKnight Brain Institute, University of Alabama 17196th Avenue South, CIRC 429, Birmingham AL 35294, USA e-mail: [email protected]
nm for MWNTs while their length can vary from one to several hundred micrometers. The arrangement of the carbon atoms in the graphene sheet can take on several conformations, armchair, chiral or zigzag. These conformations of the nanotube determine its conductivity. Nanotubes are most commonly synthesized upon a catalyst by a variety of methods including, chemical vapor deposition, electric arc discharge and laser ablation. After manufacture, CNTs are often modified to improve their biocompatibility or enable them to perform new functions by attaching various compounds to them. Lipids, DNA and various peptides can often be simply adsorbed to the CNT. If a more permanent attachment is desired, compounds may be covalently linked to nanotubes. This is most often done by incubating nanotubes with strong oxidizing agents like nitric acid, which add carboxyl groups to the ends of the tubes and any defect sites. Other groups can then be added, usually converting the carboxyl group to acyl chloride, which can then be reacted with the compound of interest. For review on CNT structure and modifications see (5,6). In this review we discuss the use of CNTs in neuroscience, focusing mainly on
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