Single Enzyme Biomineralization of Size Controlled, Water Soluble Quantum Dots

Single Enzyme Biomineralization of Size Controlled, Water Soluble Quantum Dots

Robert Dunleavy, Leah Spangler, Zhou Yang, Li Lu, Christopher J. Kiely, Bryan W. Berger, Steven McIntosh.

Biological systems have evolved several unique mechanisms to mineralize, primarily structural, inorganic nanomaterials. These biomineralization processes are inherently “green”, enabling low-cost and scalable production of nanomaterials under benign conditions in aqueous solutions. However, extending from these processes to achieve the regulated control necessary for reproducible, scalable biosynthesis of functional nanomaterials remains a central challenge. This is especially true of quantum dots (QDs), where precise size and crystal quality control is required to achieve the desired electronic properties. While several studies have described production of QDs from biological systems, the majority of these add a reactive chemical precursor, typically Na₂S, or do not provide the necessary tight control over particle size.

In this work, we describe a single enzyme capable of both the mineralization and templating of cadmium, lead, and zinc sulfide quantum dots within the quantum confined size range. The quantum dots are synthesized in the aqueous phase from normally unreactive metal acetate and L-cysteine precursors and are only formed upon the addition of the enzyme. The mineralization mechanism is proposed to consist of enzymatic turnover of L-cysteine to form reactive H₂S and is coupled to enzymatic templating of nanocrystal growth. We further demonstrate the flexibility of this approach to form core-shell and alloy nanoparticles. The biomineralized materials demonstrate aqueous phase band gap and quantum yield similar to chemically prepared materials.