Nanostructured Materials Synthesized by Deposition of Metals on Microtubule Supports
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Compared to bulk materials, nanoscale materials, with their large surface areas and possible quantum confinement effects, possess distinct electronic, optical, and chemical properties. Therefore the synthesis of defined nanostructures is of potential interest in various fields including catalysis or microelectronics. In catalysis, for example, interesting applications for metal nanoparticles emerge from an enhanced activity, good selectivity (controllable by surface modifiers), and synergistic effects in bimetallic catalysts. In electronics, a fundamental concept for miniaturization is the handling of single charges by means of single electron tunneling (SET) in ordered one-, two-, or three-dimensional arrangements of metal or semiconductor clusters. Inspired by the unique physical and chemical properties, much effort has been made to tailor defined one-, two-, or three-dimensional nanostructures ranging from ordered nanoparticle arrays to nanowires.
In biology, nanostructures are familiar objects. Biological components exhibit size dimensions from the nanometer to the micrometer size range together with exceptional molecular recognition capabilities and functionalities for distinct biochemical transformations and translocations. However, many of these biomolecules do not possess the required physical or chemical properties. DNA, for example, has the appropriate recognition capabilities, but poor electric characteristics prevent its direct use in electric circuits. On the other hand, inorganic materials such as metals or semiconductors display, for example, the desired electric or optical properties, but their controlled deposition into defined nanostructures is difficult by conventional methods. Recently, the unique features of biological systems have been explored as building blocks for bottom-up assembly or controlled deposition of novel inorganic materials and devices with advanced structures and functionalities. For example, the specific recognition properties of oligonucleotides or antibodies have been exploited for assembling metal nanoparticles into well-ordered three-dimensional aggregates. The protein cages of viruses have been used as a template for a controlled deposition and organization of metallic nanoparticles. Motivated by future electronic applications, researchers used DNA to control the deposition of metals and create conductive nanowires consisting of silver, gold, palladium, platinum, and copper.
In this article we address the template-directed deposition of metals on microtubule supports for fabricating metal nanostructures ranging from regular arrays of nanoclusters to continuous nanowires.