DNA-mediated formation of one-dimensional nanostructures

The present dissertation deals with the fabrication of one-dimensional nanostructures based on DNA templates. The aim hereby is the development of novel, conducting, DNA-based materials, which may at the end allow the programmable assembly of DNA-based electronic nanostructures, like nanoswitches and conductive nanowires. DNA is a suitable template because of its one-dimensional structure and its extraordinary self recognition properties. Due to the sequence of base pairs and the possibility to direct this sequence by modern methods for the synthesis of DNA the template is furthermore to a certain degree programmable. The multitude of binding sites at the DNA bases and the charged backbone as well as the possibility to incorporate artificial bases instead of the natural ones allows a modification of DNA with metal ions and nanoparticles. For the synthesis of the one-dimensional nanostructures presented in this work native DNA strands as well as artificially synthesized DNA duplexes were utilized. Two main strategies for the metallization are described: the immobilization of preformed nanoparticles to DNA templates and the continuous metallization of DNA strands for the generation of continuous metal nanowires. One approach investigated in this work is the immobilization of amine terminated Fe/Pt nanoparticles to neighbouring GC base pairs in native plasmid DNA via the DNA binding complex cisplatin. In this context, a variety of water soluble Fe/Pt particles stabilized by different amines were synthesized via a ligand exchange reaction and studied by means of transmission electron microscopy. The coupling of ethylenediamine stabilized Fe/Pt particles to native plasmid DNA with cisplatin could be shown by AFM. This method yielded partly decorated strands, due to a low selectivity for binding sites, and was therefore not investigated in detail. However, the versatile surface functionalization of the water soluble Fe/Pt nanoparticles in combination with the extraordinary magnetic properties of the material opens the opportunity of diverse biomedical applications. Spatially defined DNA-nanoparticle-assemblies could be obtained by immobilization of azide terminated Au nanoparticles to artificial DNA duplexes. Those DNA duplexes which were synthesized by PCR incorporate artificial alkyne labeled thymine and cytosine derivatives instead of the native bases within their sequence. The immobilization of azide terminated nanoparticles to the alkyne functionalized template could be accomplished via the Cu(I)-catalyzed Huisgen cycloaddition, the so called ‘click’ reaction. The azide functionalized Au particles were obtained by direct synthesis as well as by ligand exchange reactions in one- and two-phase systems. The resulting nanoparticles with sizes between 1-4 nm were characterized by means of AFM, TEM, UV/Vis, and ATR. After the reaction with the alkyne labeled templates, one-dimensional nanoparticle arrays could be obtained as proven in detailed TEM and AFM studies. It could be observed that the array consists of uniform nanoparticles with regular particle distance presumably caused by the space requirement of the ligand shell around the particles. A second main goal in this work was the generation of continuously metallized nanowires with tunable diameters. Therefore again alkyne labeled DNA duplexes were utilized which were reacted with a sugar azide in a further step to generate reductive groups on the surface of the strands. Incubation with Tollens solution yielded Ag nucleation sites on the DNA, which could be covered with a Ag or Au layer in a further step. The resulting structures could be characterized by means of AFM and SEM. In case of the bimetallic Ag/Au wires diameters of 10 nm and smaller could be obtained. In time dependent metallization experiments the metallization time could be identified as a size-defining variable. Furthermore, the Ag nanowires, which were synthesized according to a similar method, were characterized by means of SEM and EDX. The latter showed a diameter between 50 nm and 100 nm and could be used for electrical addressing with a nanomanipulator unit incorporated into the chamber of the SEM. A long-term objective emerging from this thesis will be the combination of both methods, the site specific continuous metallization of DNA and the spatially defined immobilization of preformed metal clusters on the DNA strand. The feasibility of both methods has been demonstrated here. In combination they give prospect to functional DNA-based devices generated by self-assembly processes in solution.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2007

Author dc:creator

• Fischler, Monika

Contributors dc:contributor

• Simon, Ulrich

• info:eu-repo/classification/ddc/540
• DNS
• Nanopartikel
• Selbstorganisation
• Chemie
• Nanodrähte
• DNA
• nanoparticles
• self-assembly
• nanowires

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123992%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:62422