Electrostatic Self-Assembly - From Proteins, Viruses, and Nanoparticles to Functional Materials

This thesis is a study on the structure and formation of materials that can be produced through self-assembly of nanoparticles in aqueous solution. Nanoparticles exhibit size-dependent properties that are modulated by the arrangement of the particles, and they are promising for the development of new functional materials. The focus is on the electrostatic self-assembly of biological and synthetic nanoparticles into hierarchical structures with properties that arise from the constituent units. Publication I studies the electrostatic self-assembly of cocrystals consisting of apoferritin protein cages and poly(amidoamine) dendrimers. A systematic series of poly(amidoamine) dendrimers with generations from two to seven were used to produce cocrystals. The experiments demonstrated that the lattice geometry and the lattice constant of the cocrystals depend on dendrimer generation. Ionic strength was used to control the structural formation and to reversible disassemble the cocrystals. In Publication II functional crystalline arrays of biological particles were formed by combining cowpea chlorotic mottle virus and avidin protein. Enzymatic activity, plasmonic, and fluorescent properties were included in the crystals, which were successfully functionalized through binding of biotin-tagged functional units to avidin. In Publication III photoactive protein-dye crystals were produced. The crystals consisted of apoferritin protein and a photoactive phthalocyanine-1,3,6,8-pyrenetetrasulfonic acid complex that is used to generate singlet oxygen under irradiation of visible light. The incorporation of the photoactive dye into protein crystals was found to be a facile approach to immobilize the dye without losing the singlet oxygen generating property. In Publication IV proteins and dendrimers were functionalized with azobenzene to obtain light-induced motion of the particles, demonstrating that even very large supramolecular complexes can be made to move in response to light. The light-induced motion could be used to arrange the functionalized particles into a periodic pattern on a substrate. In Publications V and VI highly monodisperse cationic gold nanoparticles were synthesized, and used to form electrostatically self-assembled superlattice wires together with a rod-like tobacco mosaic virus. The particles assembled in a cooperative manner yielding superlattice wires with a characteristic helical twist that was also observed in the optical properties of the material. The results of this thesis contribute to the development of new functional materials with highly ordered nanoscale structure. The thesis has especially underpinned the possibility to use nanoparticles as functional modules that can be incorporated in higher-order structures.