Biologically-templated metal oxide and metal nanostructures for photovoltaic applications

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.Cataloged from PDF version of thesis. Vita. Page 296 blank.Includes bibliographical references.In several electronic, electrochemical and photonic systems, the organization of materials at the nanoscale is critical. Specifically, in nanostructured heterojunction solar cells, active materials with high surface area and continuous shapes tend to improve charge transport and collection, and to minimize recombination. Organizing nanoparticles, quantum dots or organic molecules intro three-dimensional structures can thus improve device efficiency. To do so, biotemplates with a wide variety of shapes and length scales can be used to nucleate nanoparticles and to organize them into complex structures. In this work, we have used microorganisms as templates to assemble metal oxide and metal nano- and microstructures that can enhance the performance of photovoltaic devices. First, we used M13 bacteriophages for their high aspect ratio and ability to bind noble metal nanoparticles, to create plasmonic nanowire arrays. We developed a novel process to assemble bacteriophages into nanoporous thin films via layer-by-layer assembly, and we mineralized the structure with titania. The resulting porous titania network was infiltrated with lead sulfide quantum dots to construct functional solar cells. We then used this system as a platform to study the effects of morphology and plasmonics on device performance, and observed significant improvements in photocurrent for devices containing bacteriophages. Next, we developed a process to magnesiothermally reduce biotemplated and solution-processed metal oxide structures into useful metallic materials that cannot be otherwise synthesized in solution. We applied the process to the synthesis of silicon nanostructures for use as semiconductors or photoactive materials. As starting materials, we obtained diatomaceous earth, a natural source of biotemplated silica, and we also mineralized M13 bacteriophages with silica to produce porous nanonetworks, and Spirulina major, a spiral-shaped algae, to produce micro-coils. We successfully reduced all silica structures to nanocrystalline silicon while preserving their shape. Overall, this work provides insights into incorporating biological materials in energy-related devices, doping materials to create semiconductors, characterizing their morphology and composition, and measuring their performance. The versatility and simplicity of the bottom-up assembly processes described here could contribute to the production of more accessible and inexpensive nanostructured energy conversion devices.by Noémie-Manuelle Dorval Courchesne.Ph. D

Biomimetic engineering of conductive curli protein films

Bioelectronic systems derived from peptides and proteins are of particular interest for fabricating novel flexible, biocompatible and bioactive devices. These synthetic or recombinant systems designed for mediating electron transport often mimic the proteinaceous appendages of naturally occurring electroactive bacteria. Drawing inspiration from such conductive proteins with a high content of aromatic residues, we have engineered a fibrous protein scaffold, curli fibers produced by Escherichia coli bacteria, to enable long-range electron transport. We report the genetic engineering and characterization of curli fibers containing aromatic residues of different nature, with defined spatial positioning, and with varying content on single self-assembling CsgA curli subunits. Our results demonstrate the impressive versatility of the CsgA protein for genetically engineering protein-based materials with new functions. Through a scalable purification process, we show that macroscopic gels and films can be produced, with engineered thin films exhibiting a greater conductivity compared with wild-type curli films. We anticipate that this engineered conductive scaffold, and our approach that combines computational modeling, protein engineering, and biosynthetic manufacture will contribute to the improvement of a range of useful bio-hybrid technologies.Peer ReviewedPreprin

Fabrication of fluorescent pH-responsive protein–textile composites

Abstract Wearable pH sensors are useful tools in the healthcare and fitness industries, allowing consumers to access information related to their health in a convenient manner via the monitoring of body fluids. In this work, we tailored novel protein–textile composites to fluorescently respond to changing pH. To do so, we used amyloid curli fibers, a key component in the extracellular matrix of Escherichia coli, as genetic scaffold to fuse a pH-responsive fluorescent protein, pHuji. Engineered amyloids form macroscopic and environmentally resistant aggregates that we isolated to use as stand-alone hydrogel-based sensors, and that we trapped within textile matrices to create responsive bio-composites. We showed that these composites were mechanically robust and vapor-permeable, thus exhibiting favorable characteristics for wearable platforms. CsgA–pHuji fibers integrated in the textile allowed the final device to respond to pH changes and distinguish between alkaline and acidic solutions. We demonstrated that the resulting composites could sustain their fluorescence response over days, and that their sensing ability was reversible for at least 10 high/low pH cycles, highlighting their potential for continuous monitoring. Overall, we introduced a biosynthesized amyloid-based textile composite that could be used as biosensing patch for a variety of applications in the smart textile industry

Tracking of engineered bacteria in vivo using nonstandard amino acid incorporation

\u3cp\u3eThe rapidly growing field of microbiome research presents a need for better methods of monitoring gut microbes in vivo with high spatial and temporal resolution. We report a method of tracking microbes in vivo within the gastrointestinal tract by programming them to incorporate nonstandard amino acids (NSAA) and labeling them via click chemistry. Using established machinery constituting an orthogonal translation system (OTS), we engineered Escherichia coli to incorporate p-azido-l-phenylalanine (pAzF) in place of the UAG (amber) stop codon. We also introduced a mutant gene encoding for a cell surface protein (CsgA) that was altered to contain an in-frame UAG codon. After pAzF incorporation and extracellular display, the engineered strains could be covalently labeled via copper-free click reaction with a Cy5 dye conjugated to the dibenzocyclooctyl (DBCO) group. We confirmed the functionality of the labeling strategy in vivo using a murine model. Labeling of the engineered strain could be observed using oral administration of the dye to mice several days after colonization of the gastrointestinal tract. This work sets the foundation for the development of in vivo tracking microbial strategies that may be compatible with noninvasive imaging modalities and are capable of longitudinal spatiotemporal monitoring of specific microbial populations.\u3c/p\u3

Tracking of engineered bacteria in vivo using nonstandard amino acid incorporation

The rapidly growing field of microbiome research presents a need for better methods of monitoring gut microbes in vivo with high spatial and temporal resolution. We report a method of tracking microbes in vivo within the gastrointestinal tract by programming them to incorporate nonstandard amino acids (NSAA) and labeling them via click chemistry. Using established machinery constituting an orthogonal translation system (OTS), we engineered Escherichia coli to incorporate p-azido-l-phenylalanine (pAzF) in place of the UAG (amber) stop codon. We also introduced a mutant gene encoding for a cell surface protein (CsgA) that was altered to contain an in-frame UAG codon. After pAzF incorporation and extracellular display, the engineered strains could be covalently labeled via copper-free click reaction with a Cy5 dye conjugated to the dibenzocyclooctyl (DBCO) group. We confirmed the functionality of the labeling strategy in vivo using a murine model. Labeling of the engineered strain could be observed using oral administration of the dye to mice several days after colonization of the gastrointestinal tract. This work sets the foundation for the development of in vivo tracking microbial strategies that may be compatible with noninvasive imaging modalities and are capable of longitudinal spatiotemporal monitoring of specific microbial populations

Constructing Multifunctional Virus-Templated Nanoporous Composites for Thin Film Solar Cells: Contributions of Morphology and Optics to Photocurrent Generation

Biotemplates, such as the high aspect ratio M13 bacteriophage, can be used to nucleate noble metal nanoparticles and photoactive materials such as metal oxides, as well as organize them into continuous structures. Such attributes make them attractive scaffolds for solar applications requiring precise organization at the nanoscale. For instance, thin film solar cells benefit from nanostructured morphologies that aid light absorption and carrier transport. Here, we present a biotemplating strategy for assembling nanostructured thin film solar cells that enhance the generated photocurrent through two features: (1) a nanoporous and continuous M13 bacteriophage-templated titania network that improves charge collection and (2) the incorporation of metal nanoparticles within the active layer of the device to improve light harvesting. We demonstrate our ability to construct virus-templated solar cells by applying this strategy to depleted titania–lead sulfide quantum dot (PbS QD) bulk heterojunctions. The titania morphology produced by our biotemplate allows charges to be efficiently collected from the bulk of the active material and light that is otherwise poorly absorbed by the QDs to be harvested using metal nanoparticles that exhibit plasmon resonances in the visible range. We show that high aspect ratio bacteriophages provide a structural template for synthesizing titania networks with tunable porosity, into which PbS QDs are infiltrated to create photoactive nanocomposites suitable for photovoltaics. Upon optimization, the generated photocurrent and power conversion efficiency of the bacteriophage-templated devices demonstrate a 2-fold improvement over those of control devices made with randomly organized titania nanoparticles. When the virus is complexed with gold nanoparticles (Au NPs), silver nanoparticles (Ag NPs), or silver nanoplates (Ag NPLs) during assembly, the device performance is further improved, with Ag NPLs enhancing the short-circuit current density and power conversion efficiency by 16% and 36.5%, respectively, over those of virus-based devices without NPs. The observed trends in photocurrent enhancement match well with numerical predictions, and the role of the nanostructured morphology on the device optics was computationally explored. The challenges overcome in this work could be extended to other heterojunction devices, such as hybrid systems involving conducting polymers, as well as other biologically templated electronics.MIT Energy Initiative (Eni-MIT Energy Fellowship)National Science Foundation (U.S.) (Award No. DMR- 0819762)David H. Koch Institute for Integrative Cancer Research at MIT (NCI core grant P30-CA14051)Natural Sciences and Engineering Research Council of Canada (Postgraduate Scholarship)National Science Foundation (U.S.) (Graduate Research Fellowship Grant No. 1122374