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GREEN SYNTHESIS OF METAL NANORODS - EXPLOITING NOVEL BIOLOGICAL TEMPLATES: BARLEY STRIPE MOSAIC VIRUS VIRUS-LIKE PARTICLES
Nanotechnology has experienced a tremendous rise in the last decade. The synthesis of nanomaterials of defined structure and controlled properties is one of the most challenging part. Solution processing bottom-up fabrication techniques enables the facile synthesis of low dimension and ordered structures with low cost through the self-assembly of basic building blocks. Biotemplating has become an emerging field in which natural biomolecular objects are utilized for creating functional, hierarchical, controlled patterned structures with nanometric precision. It is a capital effective, eco-friendly and energy-efficient synthetic process. Viral biotemplating has shown great potential in electronics, environmental and biomedical devices. In recent years, in-planta produced Tobacco Mosaic Virus (TMV) and its variants have been used to produce metal nanorods and nanowires of monodisperse structures under mild conditions without the use of harsh chemical treatments although there remains much to be understood. Mass production of biotemplate, programming of viral particles of desired functionalities, manipulation for biomineralized metal materials of good quality have not been sufficiently studied to allow for directed synthesis. The fundamental studies on platform development for viral biotemplate production, design of viral proteins carrying engineered properties, and the hydrothermal synthesis of biotemplated metal nanomaterials, which create great uniformity and high coverage are of interest in this dissertation. Three experimental studies are outlined.
A novel virus biotemplate, Barley stripe mosaic virus (BSMV) virus-like particle is designed and engineered through genetic engineering. By fusing the Origin of Assembly from TMV to the transcript encoding BSMV capsid protein, the self-assembly of BSMV-VLP nanorod from microbial-based protein expression system was achieved for the first time. An alternate platform for viral particle production has been developed. Optimization of VLP expression, purification and processing conditions are performed. This developed alternative E. coli production platforms offer unique opportunities for genetic engineering and faster protein expression; therefore, the development of our system enables rapid design-build-test cycles for the engineering and production of BSMV-VLPs with desired properties. Results in this project shows the power of genetic engineering and serves as a springboard for genetic engineering of the VLPs.
Programming on BSMV-VLP is further used to decouple the VLP assembly into governing internal molecular interactions. To drive the nucleic acid free helical BSMV-VLP rod assembly and further increase the stability of capsid proteins, an identification of Caspar Carboxylate cluster in BSMV is performed. Various carboxylate residues were selected through protein crystal structure and examined systematically through experimental work. By introducing mutations on selected residues, the intersubunit carboxylate interaction of the proteins was significantly altered, resulting in an in vivo production of nucleic-acid free BSMV-VLP assembly for the first time. The change in interactions leads to increased stability of the modified VLP, enabling the formation of longer nanorods with lengths over one micrometer. Moreover, both wild-type and mutated BSMV-VLPs were shown to have great structural stability across a wide range of pHs. Overall, we exhibit experimental identification to systematically probe the key carboxylate interactions to increase the stability of proteins and drive RNA-free BSMV-VLP assembly. This project greatly expands the potential usefulness of the engineered BSMV-VLP biotemplates for a wide variety of applications.
Finally, to demonstrate the versatile uses of BSMV-VLP in biotemplating, the new biotemplate was utilized to expand understandings on the directed synthesis of metal nanostructures. By using the hydrothermal synthesis, VLPs were successfully utilized to synthesize monometallic palladium nanorods with a wide range of length scales. The VLP-mediated nanorods are more uniformly and fully-covered than the ones synthesized with in planta-produced BSMV virion. Besides, the synthesis shows an effective control over the metal nanorod diameter. The capability of BSMV-VLP was readily expanded from the synthesis of monometallic nanorods to bimetallic hybrid. In the absence of an exogenous reducing agent, mineralization of platinum, gold and copper was successfully demonstrated on the VLP. It is attributed to lower reduction barrier introduced by already-deposited palladium nanoparticles which serve as nucleation sites for subsequent metal reduction. The formation of bimetallic complexes was further supported by STEM, EDS and XPS analysis evidenced the presences of multiple metals. Overall, BSMV-VLP-mediated biotemplating using the hydrothermal synthesis has been confirmed to be a promising and feasible approach to create organic-inorganic complex nanocomposite.
Lastly, to move toward an application, the synthesized Pd nanorods coated with full coverage and great uniformity of nanoparticles were utilized as an exciting hydrogen sensing material. The developed hydrogen sensing system using a quartz crystal microbalance shows a fast response toward hydrogen as well as the ability of hydrogen detection and quantification of the adsorption capacity. This study serves as an entry point and opens up enormous possibility for next-generation of Pd-virus hybrid hydrogen sensors.
Taken together, this dissertation has demonstrated the engineering and production of a novel BSMV virus-like particle bacterial system. This alternative platform and developed parameter space for VLP production is genetically tractable and requires significantly shorter processing duration for large-scale and mass production. The BSMV-VLP biotemplated metal nanomaterials present great qualities and controllable dimensions. This approach has explored the synthetic palette and opened up enormous possibilities in the bottom-up nanofabrication of versatile and tunable organic-inorganic nanoscaled complex and would facilitate future engineering industrial applications.