DNA-Controlled Self-Assembly Of Hybrid Nanostructures And Functioning Nanomachines

The main topic of this thesis is about the controllable assembly of inorganic nanostructures and supramolecular nanomachines using designed DNA sequences, which falls into the area of DNA nanotechnology.The appeal of DNA to nanoscience and nanotechnology is threefold:firstly,it is a naturally occurred nanoscale building block,which can be chemically manufactured on a solid phase DNA synthesizer with single base accuracy,and assembled in a salt-containing buffer through a simple heating-up and cooling-down cycle;secondly,well-developed chemistry and molecular biology tool-kits are readily available for operating,modifing,replicating, clipping and joining DNA molecules to further tailor their structures and functions; and thirdly,the base sequences in DNA can be easily encoded and exploited for programmed self-assembly,resulting in virtually any defined structures and patterns on the nanoscale in an extremely accurate and predictable way.This thesis tried to employ DNA as a supramolecule helper to facilitate the assembly of linear heteronanostructures between gold nanoparticles and single-walled carbon nanotubes in order to associate special and novel properties with designed hybrid nanosystems.We would also attempt to build a DNA structured nanomechnical device that can have some close-to-reality functions such as grabbing or releasing an object at will.Following are detailed descriptions of these results:Water-soluble gold nanoparticle(AuNP) linear arrays on single walled carbon nanotubes(SWNTs) were obtained via a DNA-assisted self-assembly process.This work took advantage of non-covalent interactions between DNA bases and single-walled carbon nanotubes(a technique established by Zheng et al.at Dupont Central Research and Development) to introduce multiple thiol groups on the surface of a SWNT,which then served well as a novel template for the assembly of linear gold nanoparticle arrays.The native rigidity of SWNTs made them especially suited as linear assembly templates and rendered the resulting gold nanoparticle linear arrays very good quality and free of any self-entanglements,which often happen to a softer template such as a DNA double helix.The as-formed AuNP-SWNT hybrids were isolated by agarose gel electrophoresis and their structures were validated through atomic force microscopy(AFM) imagings.Various control experiments were designed to further verify our proposed assembly scheme.The DNA-wrapped single-walled carbon nanotubes,as a new type of nanoscale building blocks for DNA directed material assembly,should also be usable for the assembly of various other nanomaterials with distinct properties.The next goal of our research is to seek possible applications of these hybrid nanostructures in bio-detections, nanoelectronics/photoelectronics and nano-catalyses.The next pursuit of this thesis was to build a pair of DNA nanomechanical tweezers that can be easily operated to recognize,capture,hold and release an object on demand.The most difficult part of this work was to find a suitable way for the very tiny tweezers to firmly hold an object between its two mechanical arms.We made use of a non-canonical base-pairing mode called Hoogsteen hydrogen bonding to fulfill this challenging requirement.The DNA molecular tweezers could then be operated to interact with a DNA structured object at lowered pH.The DNA object helically wrapped around the tweezers' arms and was then firmly held after the tweezers being zipped close.Opening the tweezers via a DNA strand-displacement process would then release the object to solution where the Hoogsteen bonding was much weakened at increased pH.A native polyacrylamide gel electrophoresis(PAGE) in combination with a fluorescent resonance energy transfer(FRET) technique was used to demonstrate the functioning of the catch and release cycles of the tweezers.Further research can be carried out to integrate the tiny tweezers into large DNA arrays that will allow us to monitor the functioning of this new device in real time with the help of modern imaging techniques,such as atomic force microscopy(AFM).We also tried to use a very simple molecule,ethylenediamine,to switch the electrostatic assembly and disassembly of gold nanoparticles and DNA-wrapped single-walled carbon nanotubes based on pH controlled protonation-deprotonation processes of ethylenediamine.We used optical absorbance and centrifugation-facilitated precipitation to monitor the above aggregation-dispersion cycles.Transmission electron microscopy(TEM),dynamic light scattering(DLS), and gel electrophoresis were also employed to further check the dispersion states of the gold nanoparticles before,during and after the cycling experiments.This strategy did not rely on any specific surface-modified chemical groups and should,with only slight modifications,be easily extended to other interesting systems.The most prominent and attractive feature of this method lied in the fact that it was an extremely simple,effective and general process as compared to other developed strategies for the same purpose in literature.