Biomineralization, the process by which living organisms generate minerals, has recently gained interest as a route to green synthesis of crystalline materials under ambient conditions for energy and catalysis applications. Semiconductor quantum dots are desirable for their size-tunable optical and electronic properties but are currently cost-limited in many commercial uses due to the current high temperature, inorganic synthesis routes. We will discuss our recently developed direct, single enzyme, biomineralization route for synthesis of metal sulfide and metal selenide quantum dots. Previous metal chalcogenide biomineralization routes typically either utilize a biomolecule for templating of a chemical mineralization step, or lack tight control over size or composition of the particles. In contrast, the cystathionine γ-lyase (CSE) enzyme developed in our group both templates growth and catalyzes mineralization by generating the reactive sulfur species H2S from the amino acid L-cysteine in the aqueous phase. All of these biomineralized quantum dots are produced in the aqueous phase at 20-37°C under atmospheric pressure, and can be phase transferred to the organic phase if necessary for application. Specifically, we are able to synthesize size controlled CdS, PbS, ZnS, Cd1-xZnxS and CuInS2 nanocrystals. CSE is also capable of directly mineralizing the analogous metal selenides CdSe upon switching the precursor amino acid to selenocysteine. We also demonstrate the biomineralization of core/shell structures of these materials CdSe/CdS, PbS/CdS, CdZnS/ZnS, and CuInS2/ZnS using a sequential growth method. Tunable optical properties are confirmed by absorbance and photoluminescence measurements. HRTEM and HAADF are utilized to determine the size distribution and crystal phase of the nanocrystals, while single particle XEDS confirms the composition. The functional properties of the materials are demonstrated by their incorporation into quantum dot sensitized solar cells and their use as fluorescent markers in the bio-imaging of cancer cells.

Single-enzyme direct biomineralization of metal chalcogenides nanocrystals with tunable optical properties

253rd National Meeting (2017)

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