Controlled synthesis and ordered assembly of Co3O4 nanowires using genetically engineered bacterial flagella as biotemplates (Final Technical Report)
Year: 2021
Type: report
Abstract: We conducted comprehensive investigations from 7 different but closely related aspects to achieve most of the goals in our proposed research. Yet, we were not able to carry out experiments to assemble the Co3O4‐flagella NWs into highly ordered 2D and 3D structures. This was partly impacted by the pandemic. Besides the pandemic, the scientific challenge in the 3D assembly of Co3O4 NWs was their low magnetization, which requires the NWs to have enough thickness to be responsive to the external magnetic field. But the thick NWs were not mechanically strong enough and broke easily into short pieces, making it very difficult to conduct the 3D assembly experiments. Below is a brief summary of the conducted projects. 1. Display of foreign peptides onto flagella through genetic engineering. We completed the recombinant plasmid construction for all the peptide sequences. With modified procedures, we succeeded in flagella expression and purification for all the peptide sequences except for K10 and K20. In our mineralization trials, we found that flagella displayed with positively charged peptides were not favored for Co3O4 mineralization. Therefore, in our following investigation, we mainly focused on the flagella displayed with negative charges. 2. Synthesis of Co3O4 nanowires (NWs) through direct nucleation on genetically engineered bacterial flagella templates. To obtain homogeneous Co3O4 NWs with high crystallinity, engineered flagella displaying charged amino acids were used as templates. We first attempted to carry out the synthesis using Co(NO3)2, NaOH and H2O2 as precursors, but found that this system can hardly generate thick, crystallized Co3O4 NWs. In our second attempt, we employed a novel CoCl2 and NaBH4 based synthetic system. In this system, we were able to nucleate and grow Co3O4 NWs on flagella template through a one-step reaction at room temperature. It is shown that icosa-glutamate (E20) displayed flagella formed decent quality Co3O4 NWs comparing with other sequences such as penta-lysine(K5) and deca-glutamate (E10). We also studied the Co3O4 NWs crystalline process by sampling at multiple time points, as well as the antibacterial properties of thin films fabricated out of the flagella templated Co3O4 NWs. 3. Synthesis of Co3O4 NWs through assembly of preformed Co3O4 nanoparticles onto flagella templates. In addition to direct nucleation and growth of cobalt oxide nanowires on engineered flagella, we also proposed to assemble pre-synthesized Co3O4 nanoparticles onto flagella. Our first attempt to employing aqueous-prepared Co3O4 nanoparticles for assembly failed to the severe aggregation issue of NPs upon polyethyleneimine (PEI) coating. Later, we tried to synthesize Co3O4/Fe3O4 hybrid nanoparticles in the oil phase followed by a phase transfer process to achieved 1D assembly of the magnetic hybrid NPs onto flagella. 4. Length control of flagella through depolymerization and repolymerization. To control the length of flagella, so as to obtain Co3O4 NWs of tunable length, we proposed a seeded regrowth approach, which involves depolymerization of the harvested flagella into flagellin monomer, and repolymerization of the monomer in the presence of short flagella seeds. We have successfully produced seed and monomer solution for flagella reconstruction through freezing/thawing and heating methods. We also confirmed that by simply mixing seeds solution with the monomer solution at room temperature, the monomers were able to repolymerize into long filaments and the shape, such as pitch wavelength and curvature, was indistinguishable from intact flagella. In addition, we also attempted to investigate the dynamics of seeded flagellin repolymerization and flagella elongation process by using in situ AFM. 5. Separation of flagella with different length through density gradient ultracentrifugation. We tried to separate flagella with different length through density gradient ultracentrifugation to further narrow down the length distribution of repolymerized flagella. We adopted two different strategies to create media containing continuous density gradient. We found that in one of the methods, short flagella (less than 500 nm long) can be separated very well, however, longer flagella were not well sorted. In the other method, all the flagella could generally be sorted by length in a relatively wide range. 6. Tuning Electrostatic Nanoparticle Assembly on Filamentous Protein-based Biotemplates We conducted some further investigation of the interaction between PEI coated NPs and various biotemplates, including the assembly mechanism and the effect of different parameters including PEI molecular weight and nanoparticle size. In addition, we believe that such an electrostatic interaction induced assembling strategy should be general and should not be limited to the types of NPs and biotemplates. To test this hypothesis, we expanded our assembly method to two other types of NPs, namely iron oxide magnetic NPs (MNPs) and quantum dots (QDs), and two other types of linear biotemplates, namely filamentous phages and pili. 7. Assembly of CTAB‐coated nanoparticles onto flagella biotemplates. In addition to the polymer (PEI) coated NPs, we also attempted to investigate the electrostatic interaction of NPs coated by small positively charged molecules, namely cetyltrimethylammonium bromide (CTAB), with flagella. We conducted our initial study using the well‐known gold nanorods (AuNRs) as a model nanoparticle, the surface of which is coated with a double CTAB layer. With free flagella in the solution phase, AuNRs generally formed a two‐string pattern along the two lateral sides of the templates, while single‐string pattern dominated on the immobilized flagella. In addition, the steric effect also controlled the inter‐particle distance of the AuNRs.
DOI: 10.2172/1772896
Institution: University of Oklahoma
Language: English
Topic: Diatoms and Algae Research
Subfield: Biomaterials
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
Funder: U.S. Department of Energy
OpenAlex ID: W3214150203