Biointerfacing Living Cells With Nanostructured Biohybrid Layer For Surface Functionalization

Non-biogenic cell surface functionalization(so called cell surface functionalization) without complicated genetic process can not only improve cell stability, but also endow cells with new functionalities, which have been widely used in nano-biotechnology, energy, environment, chemistry and biomedical research. Recently, plenty of nanomaterials have been used for cell surface functionalization. The benefit of having artificial nanostructured materials on cell surface is improving cell stability and manipulability as well as endowing cell with multifunctionalities. However, it is still a big challenge to fabricate biocompatible interfaces between living cells and abiotic materials.Natural bioactive molecules and Au nanoparticles are biocompatible, and also they can interact with each other to form well-defined structured biohybrids. The biohybrids could self-assemble onto cell surface to form desired biocompatible interface. In this thesis, we fabricate this biocompatible bioactive interface on living cell surface by self-assembling process. The nanoporous structure of the bio-interface facilitates mass communications. Furthermore, the bio-interface can act as a platform to induce inorganic shell formation, as a result of cell@bilayers shell structure. The bilayers shell could not only enhance cell stability, but also endow cell with extra functionalities to expand the applicabilities, such as high light-tolerance, acid-base adaption, natural toxins resistance and magnetic property. Finally, we develop a novel method to create a self-repairing shell by using the self-assembled biohybrids. More details are shown as follows:Firstly, we choose cyanobacteria as the model of photosynthetic cells and create a single cell photosynthetic bioreactor. We have developed a method to interface an individual cyanobacterium with nanoporous bio-interface within mesoporous silica nanoshell through self-assembly. This bilayers nanoshell offers efficient functions to create a single cell photosynthetic bioreactor with a high stability, reusability, and photosynthetic activity.Secondly, we create a single cell desulfurizing bioreactors by using desulfurizing bacteria. Au@L-lysine biohybrids have been developed to self-assemble on the surface of an individual desulfurizing cell to form a nanothin and nanoporous shell. The shell not only endows the encapsulated cells with reusability, but also offers a platform to incorporate inorganic nanomaterials for post-functionalization. For example, titania nanoparticles can be introduced to enhance 24% of desulfurizing activity. Introduction of Fe3O4/SiO2 nanocomposites on cell surface can endow the cells with magnetic separation behaviour. The encapsulated cells can be easily and quickly separated from solution by an external magnetic force in 5 seconds.Thirdly, we use yeast cells as the example to investigate the formation mechanism of biohybrid interface and bilayers nanoshell. We also study the protection mechanism of Au@L-cysteine bilayers-shell encapsulated cells in complex artificial environment involving three or more harsh conditions. The encapsulated cells show very good reusable behavior that they maintain 79%(±2%) of initial activities, even after 10 cycles.Finally, we use yeast cells as model of eukaryotic cells and cyanobacteria as model of prokaryotic cells, respectively and investigate self-repairing property of biohybrid shells. It has been proven that the biohybrids could actively self-assemble onto naked cell surface to repair the broken shell caused by cell proliferation. Moreover, the encapsulated cells maintain higher activity under UV radiation that the encapsulated cells remain 98%(±6%) of the initial activity while native cells are quickly dead within 5 hours.These above mentioned strategies of creating a biohybrid interface on living cell surface for surface functionalization offer general, facile and unique approaches for the encapsulation of cells with long-term viability, extraordinary stability, high activity and multiple functionalization. It is also believed that our strategy developed here would increase the number of tools available for more functionalities in cell-based nanobiotechnology.This thesis includes six chapters. In Chapter 1, we introduce the development of cell surface functionalization, category and applications. In Chapter 2, we use photosynthetic cells to fabricate single cell photosynthetic bioreactors. In Chapter 3, we use desulfurizing cells to create single cell desulfurizing bioreactors. In Chapter 4, we discuss self-assembling and formation mechanisms of cell-in-biohybrid layer structure. In Chapter 5, we also investigate the self-repairing property of biohybrid layer. In Chapter 6, we conclude the above mentioned strategies of creating biohybrid interface on cell surface and outlook on further development of cell surface functionalization based on our work.