E.Coli Biofilm-enabled Bio-inorganic Hybrid Materials:Designs And Applications

Bio-inorganic hybrid material systems hold great promise for applications in both artificial photosynthesis and functional composite materials.Existing strategies for the preparation of bio-inorganic hybrid materials often involve the use of various biological and bio-inspired molecules or templates including but not limited to DNA origami,peptides,proteins,phage and bacteria.Among these systems,DNA templates have poor structural stability and are usually difficult to achieve large-scale production.Peptides and proteins require tedious synthetic and purification processes,while the phage materials have limited functional flexibility as only short peptides could be fused to its capsid proteins.Bacteria have also been utilized for direct deposition of inorganic materials on cell surfaces,but the efficiency is usually low due to low surface areas.In addition,the direct contact between inorganic materials and cell surface often causes damages to bacteria cells.In short,the current state-of-art hybrid material systems are mostly static,and they often lack the hierarchy and higher-order complexity of natural material systems.Last but not least,these approaches are not fit for large-scale production owing to the tedious preparation and purification procedures.To address the aforementioned problems,this dissertation draws inspiration from natural hierarchical material systems?such as teeth,bones and shells?and propose the use of Escherichia coli?E.coli?biofilms as dynamic self-assembling templates to construct novel bio-inorganic hybrid structures.The first strategy essentially builds upon programmable E.coli biofilm formation in which chemical or light-inducible gene circuits?pDawn?,assisted with nitrilotriacetic acid?NTA?coordination chemistry,could spatiotemporally regulate the dynamic assembly of nano-objects on curli fibers.In parallel,functional biofilms containing fused A7 peptides were applied as biological templates for biomimetic mineralization of CdS nanocrystals directly onto the functional curli nanofibers.Notably,the resultant bio-inorganic hybrid structures based on the two strategies both showed hierarchical structural features and had been successfully utilized for the design of catalytic reaction systems and semi-artificial photosynthesis systems.In my first work,templated assembly of NTA-capped nano-objects onto curli fibers was established through molecular recognition based on“NTA-Metal-His”coordination chemistry.Notably,the discrete and heterogeneous assembly of nano-objects along curli fibers was achieved through co-incubating NTA-decorated nano-objects and designer cells under biofilm formation conditions.Additionally,large-scale coatings comprising nano-objects on various surfaces with distinct functionalities could be easily constructed owing to the inherent adhesion of biofilms towards various interfaces/surfaces.To further showcase the potential of my designer cell-based strategy for more complex nano-object assembly,I demonstrated layer-by-layer assembly of nano-objects on both planar 2D and curved 3D substrates through sequential addition of different nano-objects to culture media.This strategy not only demonstrates the use of dynamic biofilm formation for engineering conceptually new types of materials,but also produces bio-inorganic hybrid structures that have potential applications in electronics,optoelectronics and wearable devices.I next turned my attention for patterned assembly of nano-objects by applying a light-sensing E.coli strain.As the bacteria harboring a blue light-induced gene circuit could sense blue light and responded to produce biofilm curli fibers with exquisite spatial control,I therefore achieved micro-to macro scale patterning of discrete or mixed fluorescent quantum dots on planar surfaces through programmed light regulation with living cells.Meanwhile,I also demonstrated a wide range of quantum dot patterns by using pre-defined masks with featured graphs.Such programmed light regulation coupled with dynamic self-assembly could open up opportunities for creating new nanotechnologies based on living cells.Immobilization is considered a feasible strategy for addressing challenges including toxicity and nanomaterial pollution for nano-scale objects.Building upon the established nano-object immobilization approach using engineered E.coli biofilms,I further demonstrated scalable,tunable and reusable catalytic systems including biofilm-anchored gold nanoparticles to degrade the pollutant p-nitrophenol and biofilm-anchored CdSeS@ZnS quantum dots for photo-catalytic hydrogen production.In addition,the E.coli biofilms could also been integrated with in situ polymerization of polypyrrole to produce conductive composite materials.In my second strategy,a biomimetic mineralization approach was employed to construct bio-inorganic hybrid materials.Specifically,biomimetic mineralization of CdS nanocrystals on biofilms was achieved through engineering functional curli nanofibers containing CsgA_A7 proteins in which A7 was a previously reported CdS-binding peptide.The resultant biofilms/CdS hybrid materials could be further harnessed for designing artificial photosynthesis systems including photo-catalytic reduction of trimethylpyruvic acid to L-t-Leucine and light-induced hydrogen production.In summary,I successfully produced novel bio-inorganic hybrid structures by using a programmable E.coli biofilm platform and further explored the applications of these hybrid structures in constructing electronic device,recyclable catalysis and artificial photosynthesis systems.The engineered biofilms could serve as a compatible interface for assembly and deposition of inorganic components,preventing direct contact of nano-objects with cell membrane and thus reducing potential damages of inorganic nano-objects to the cells.Natural biofilms have many extraordinary functional attributes including evolvability,environmental responsiveness,self-regeneration,excellent mechanical properties,and ultra-stability in extreme and hostile environments.A very large number of bacterial species are known to produce biofilms,which can exhibit variable material properties,including for example Geobacter species that produce biofilms that are electrically conductive.I anticipate that,apart from important applications in catalysis and artificial photosynthesis,the constructed biofilm based bio-inorganic hybrid material systems will hold great promises in applications for electronics,photonics and energy devices.