DNA-Polymer conjugates toward self-assembled polymerorigami architectures
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Abstract
The advent of DNA nanotechnology inaugurated a new era of defined, highly controllable nanostructures, equipping scientists with the tools to design nanoscale objects at the molecular level. The precise nature of DNA sequences to build architectures unlocked new possibilities and new material classes, particularly suited for demanding applications such as biosensors, nanocarriers, and templates for reaction cascades. The precise assembly of DNA-origami nanostructures offers a unique opportunity to combine them with other materials, such as polymers, in order to create distinct two- and three-dimensional hybrid materials with nanometer precision. Therefore, DNA strands can be modified with polymers, integrating the functionality and stimulus-responsive characteristics of the polymer world with the programmability of DNA, allowing the creation of conjugates with distinctive attributes, including pH and temperature responsiveness, superstructure formation, fluorescence or cell-surface binding.
The main goal of this thesis was the design, preparation and characterization of DNA-polymer conjugates with special focus on their synthesis and purification in order to achieve DNA-origami objects with nanoscale patterned surfaces. Therefore, reversible addition-fragmentation chain-transfer (RAFT) polymerization was performed to create a wide repertoire of water-soluble polymers of three different polymer classes (acrylates, methacrylates and acrylamides) with defined molecular weight. The advantage of RAFT polymerization is the usage of already pre-functionalized chain transfer agents (CTAs) to obtain end-functionalized polymers. Subsequently, a grafting to approach was adopted to conjugate DNA with the synthesized polymers, requiring careful solvent selection and reaction optimization to achieve successful coupling and high yields (Chapter III.I). Following the coupling reaction, the reaction mixtures were purified using a newly developed protocol for anion exchange chromatography. This method allows for the purification of larger reaction scales than other purification methods, such as reverse phase HPLC. Additionally, it is suitable for the purification of various DNA-polymer conjugates and those containing different sized blocks copolymers consisting of DNA or polymer segments (Chapter III.II). Notably, this purification method permits the recovery of unreacted DNA sequences for reuse and therefore is resource saving. Furthermore, the obtained DNA-polymer conjugates were employed to create polymer patterns with nanometer resolution on DNA-origami through annealing with complementary DNA strands protruding from the origami surface. This versatile strategy allows the design of functional, diverse surface modifications on a single DNA nanostructure, allowing precise 3-D engineering of complex nanoscale objects (Chapter III.I).
In summary, this study paves the way for obtaining a wide range of DNA-polymer conjugates formed with high yields and excellent accessibility, including an easy-to-use, widely applicable method for purification. This lays the groundwork for future applications. Additionally, the synthesized DNA-polymer conjugates have been demonstrated to be effective in serving as versatile surface coatings of DNA-origami nanostructures, yielding dense and well-defined surface patterns. Furthermore, they offer the capability for multipatterning of different polymer species on a single architecture, thereby expanding their utility and versatility.