Biological systems have evolved several unique mechanisms to produce inorganic nanomaterials of commercial interest. Furthermore, bio-based methods for nanomaterial synthesis are inherently “green”, enabling low-cost and scalable production of nanomaterials under benign conditions in aqueous solutions. However, achieving regulated control of the biological processes necessary for reproducible, scalable biosynthesis of nanomaterials remains a central challenge. This is especially true of quantum dots (QDs), which are nanocrystals made from seminconducting metals whose diameter is smaller than the size of its exciton Bohr radius, leading to size-dependent changes in their optical properties. Several studies have described production of QDs from biological systems, but without control over particle size or composition.<br/><br/>In this work, we describe the isolation, selection and characterization of a bacterial system capable of regulated, extracellular biosynthesis of metal sulfide QDs with extrinsic control over nanocrystal size. Using directed evolution, we isolated and engineered a bacterial strain (SMCD1) to (1) exhibit enhanced tolerance against aqueous cadmium acetate (2) produce soluble, extracellular nanocrystals and (3) regulate nanocrystal size by varying growth conditions. We estimate yields on the order of grams per liter from batch cultures under optimized conditions, and are able to reproduce the entire size range of CdS QDs described in literature. Furthermore, we are able to generalize this approach to not only cadmium, but PbS QDs as well. Investigation of purified QDs using ESI-MS reveals several putative proteins that may be involved in biosynthesis, and current work is aimed at improving photoluminescent properties as well as long-term aqueous stability. Nonetheless, our approach clearly demonstrates the ability of biological systems to produce advanced, functional nanomaterials, and provides a template for engineering biological systems to high-value materials such as QDs at cost and scale.<br/><br/>This work was supported by the National Science Foundation (Grant #1332349).

Scalable biosynthesis of quantum dots: evolution of size selectivity, solubility, and extracellular production

249th National Meeting (2015)

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