Binary Planet–Satellite Nanostructure Using RAFT Polymer
by Wentao Peng
Date of Examination:2020-03-18 // postponed to 2020-06-05
Date of issue:2020-08-06
Advisor:Prof. Dr. Philipp Vana
Referee:Prof. Dr. Philipp Vana
Referee:Prof. Dr. Alec Wodtke
Referee:Prof. Dr. Michael Buback
Referee:Prof. Dr. Ricardo Mata
Referee:Prof. Dr. Sven Schneider
Referee:Prof. Dr. Andreas Janshoff
Persistent Address:
http://dx.doi.org/10.53846/goediss-8103
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Abstract
English
This thesis provides a series of strategies to fabricate hierarchically arranged nanohybrids from distinct nanoparticles using polymer linkers. Benefit from the controlled reversible-deactivation radical polymerization technique, the topology and size of the polymer linker can be precisely controlled, which further enables full control over the size and architecting of the binary nanostructures. Reversible addition-fragmentation chain transfer (RAFT) polymerization was employed to synthesize polymers with narrow molecular weight distribution while inherently carrying the strong aurophilic and argentophilic trithiocarbonate moieties on their chain termini. Start on the basis of the strong affinity of RAFT terminated polymer to the surface of gold and silver, the gold-planet–silver-satellite nanostructures are fabricated by firstly creating four-arms star RAFT polymer capped gold nanoparticles as a globular scaffold using a grafting-to approach. The multi-arm design of the polymer enables further linkage to the silver nanoparticles yielding a planet–satellite-like nanostructure. The strengths of this approach include the fine-tuning of interparticle distances on the nanometer scale by tailoring the size of the star polymer linker. The gold-planet–silver-satellite nanostructure possesses significant plasmonic coupling phenomena making it potentially a very powerful tool for surface-enhanced Raman application. This thesis focuses further on the creation of binary planet–satellite nanoparticles with more distinct nanoparticles. This binary nanostructure is designed for the application of nanopatterning on a substrate. The final goal is to implement the highly ordered arrangement of both nanoparticles as a binary template for the cell-response experiment. Under the consideration of the chemical feasibility and the following biological accessibility, silica is chosen as the nano-planet while gold as the satellites. This thesis established a general and straightforward method to fabricate silica-planet–gold-satellite nanostructure with full control of the structural details, i.e., the number of satellites, interparticle distance, and the size of the satellite nanoparticles. In this approach, surface-initiated RAFT polymerization is implemented to obtain a well-defined polymer brush on the silica surface featuring trithiocarbonate moieties at the polymer chain termini which allows further attachment of noble metal nanoparticles. AuNP is chosen as the satellite nanocomponent due to its well-established protocols for the cell-response experiments in the previous studies. Transmission electron microscopy (TEM) shows that the silica-planet–gold-satellite nanostructure can self-assemble into a highly ordered hexagonal pattern on carbon film by simply drop-casting. The interparticle-distance between planet and satellite nanoparticles can be precisely controlled between 10 to 50 nm range which meets the design of the cell-response experiment. Based on these results, the polymer-based planet–satellite nano-assemblies have a very high potential to be applied as a unique and powerful template for creating a 2D binary bifunctional nanopattern. To unfold this feature, a method for producing a homogenous monolayer of the planet–satellite nanostructure on the CaF2 surface is established by using dip-coating technique. The polymer component is successfully removed by plasma treatment exposing the nanoparticles for further chemical or biological modification. According to the cell experiments, CaF2 is found to be an unsuitable substrate for the desired task due to the insufficient passivation (PEGylation) toward the labeling peptide. A method of transferring both gold and SiO2 nanoparticles onto hydrogel is established by introducing specific linker molecules on gold and SiO2 nanoparticles and successive photopolymerization with PEG-diacrylate. Furthermore, the RAFT-polymer functionalized nanoassemblies can quickly expend their utility by taking advantage of its inherent flexibility in the design of the polymer structure and nano component. Two distinct strategies are applied to build new features into the nanoassemblies. The first strategy uses RAFT/thiol terminated polyethylene to create an efficient synthesis route for the self-assembly of gold/silver-core–PE-shell nanohybrids. This nanohybrids successfully inherit the unique solution behavior of PE. The second approach utilizes the microemulsion technique to achieve a one-to-one silica coating of ~7 nm magnetite nanoparticles and introduces the favored superparamagnetism to the nanosystem. Owing to the silica coating and polymer shells, the magnetic interaction between each magnetite nanoparticle is effectively inhibited, which is highly favored in the realm of magnetic hyperthermia applications.
Keywords: Nanopatterning; RAFT polymer; Gold nanoparticle; Silica nanoparticle; Magnetite nanoparticle; Silver nanoparticle