Self-Assembly Of DNA And Polymeric Core-Shell Micelles And Its Applications

Self-assembly of nanoparticles aims at fabrication of objects sized tens of nanometers to several microns or even larger with complex structure, uniform morphology and specific function, which are inaccessible by chemical synthesis and micro-fabrication. Anisotropic interactions between particles are thought necessary for particle self-assembly which is analogous to molecular self-assembly, and various superstructures by self-assembly of anisotropic particles have been predicted. Experiment studies revealed that it is easier for anisotropic soft particles to self-assemble into uniform and stable superstructures than rigid ones; solvation of anisotropic soft particles counteract the isotropic van der Waals interaction that can interfere self-assembly, and soft particles adjust their anisotropy to enable the formation of stable superparticles. Isotropic soft nanoparticles can also self-assemble into various superstructures. They are isotropic in common solvents, and during self-assembly in selective solvents, they undergo deformation and sufficient material redistribution into anisotropic ones. The self-assembly is also driven by anisotropic interactions, which is induced during self-assembly rather than in the particles as synthesized. In Chapter1, self-assembly of nanoparticles was reviewed and the regulatory role of flexibility was emphasized.Nature provides marvelous examples for nanoparticulate self-assembly. By mimicking chromatin compaction in eukaryotic cells, we developed two-stage self-assembly between DNA and poly(ethylene glycol)-b-poly(4-vinylpyridine)(PEG-b-P4VP) core-shell micelles (Chapter2). In the first stage, DNA organizes the micelles exclusively into the strings very similar in both morphology and structure to the10nm chromatin fibers. During that stage, the different strings in the system formed and evolved in a similar manner and a similar step. In the second stage, the preorganized micelles self-assemble along the strings into core-shell solenoidal nanofibers, which resembles the second stage chromatin compaction in the mechanism. A number of DNA/sphere systems were studied and kinetically trapped structures were inevitably produced in the reported systems because the DNA/sphere interactions were relatively strong. Differently, in our system, the interaction strength between DNA and PEG-b-P4VP micelles can be adjusted by pH of the medium. In a weakly interaction system, we obtained the thermodynamic stable products that are consistent with computer simulations. The self-assembly can be used for tailored synthesis of nanofibers. Monodisperse nanofibers were obtained by using monodisperse linear DNA, and the length of the nanofibers can be controlled by the size of the DNA. Thick nanofibers can be produced from self-assembly between larger micelles and DNA. Nanofibers with different shells can be prepared by varying the shell-forming components of the micelles. Self-assembly of two different micelles led to binary nanostructures. Organic/inorganic hybrid nanofibers can be fabricated by deposition of inorganic components on polymeric nanofibers as the template. In addition, the gram-scale synthesis can be achieved by using larger volume and concentrated reagents.Self-assembly of circular plasmid DNA and polymeric micelles can produce polymeric nanorings. In Chapter3, we realized controlled synthesis of polymeric nanorings by varying the plasmid size, micelle size, temperature and pH for self-assembly. Larger plasmid DNA led to larger nanorings, and larger micelles led to smaller nanorings. The compaction ratio of DNA on the nanorings increased with the electrostatic interaction between DNA and micelles, so higher temperature and higher pH for self-assembly can produce larger nanorings.In Chapter4, we developed another pathway for preparation of polymeric core-shell nanofibers, also using PEG-b-P4VP and DNA. The molecularly solubilized PEG-b-P4VP solution and DNA solution were mixed together before micellization of PEG-b-P4VP, and then selective solvent (water) was added into the mixture. By using linear DNA sized tens of thousands bps, micron-sized nanofibers were produced. The self-assembly was tracked by laser light scattering and TEM. Before micellization, DNA and block copolymers associated into linear structures with block copolymer grafting loosely on the DNA backbone. With further addition of water, micellization occurred around DNA, and nanofibers formed. The critical water content for micellization is lower than that of block copolymer, indicating that the formation of the nanofibers was collaboratively driven by both hydrophobic interaction and electrostatic interaction. Different pathways lead to same objects, implying that the core-shell nanofibers are thermodynamic products of the system. The post-micellization pathway cost less time for preparation of the nanofibers than pre-micellization pathway. Incorporation of iodine into quaternized P4VP can make insulating polymeric nanofibers conductive, and the conductive nanofibers become insulating after reduction of iodine. According to this, micro-device based on conductive polymeric nanofibers was fabricated. By using current-voltage curve measurements, SO2gas can be detected with the detection limit of0.4mg/L. The device can be used repeatedly, because the iodine ion can oxidized into iodine by exposing the used device in air.By using nanofibers as template, we prepared organic/inorganic hybrids. In Chapter5, superparticles of mesoporous silica/polymer hybrid nanofibers coated with PEG were produced by deposition of mesoporous silica onto positively-charged polymeric core-shell nanofibers; the deposited silica neutralized the positive charges and caused the aggregation of mesoporous silica/polymer hybrid nanofibers into superparticles. The superparticles have stacking voids sized tens of nanometers which allows fast mass transport and thus facilitate the absorption of dyes by the mesopores on the hybrid nanofibers. The PEG on the superparticles can resist non-specific protein absorption. We used the superparticles for purification of protein-dye conjugates, i.e. removing the individual dyes after labeling reaction of protein by dyes. In a model system of BSA-rhodamine B coujugates, by simply mixing the superparticles with the reaction solution, the unconjugated dyes can be removed completely while98%of protein-dye conjugates remains in the final solution. The whole process of purification can be completed within10min. Our method is simple, efficient, fast and cheap, compared to the existing methods such as gel filtration, dialysis, HPLC and repeated precipitation and resolubilization.In Chapter6, hybrid nanofibers with inorganic nanoparticles were prepared in three different methods.1. Self-assembly of DNA and micelles containing Fe3O4superparamagnetic nanoparticles in micellar cores produced superparamagnetic nanofibers. The nanofibers preserve the superparamagnetic properties and have amplified magnetic moments.2. In-situ reduction of HAuCl4on the polymeric nanofibers led to Au nanoparticle/polymer hybrid nanofibers.3. Through self-assembly of Au nanoparticle-DNA conjugates and polymeric micelles, hybrid nanofibers end-capped with Au nanoparticles and graft superstructures with Au nanoparticles as core and nanofibers as arms were obtained.In Chapter7, by varying the shell-forming components of the micelles, we obtained mixed-shell nanofibers, thermo-sensitive polymeric nanofibers and polymeric nanofibers containing alpha-cyclodextrin on their shells.