Single Enzyme Direct Biomineralization of CdSe and CdSe-CdS Core-Shell Quantum Dots

Abstract

Biomineralization is the process by which biological systems synthesize inorganic materials. Herein, we demonstrate an engineered cystathionine γ-lyase enzyme, smCSE that is active for the direct aqueous phase biomineralization of CdSe and CdSe-CdS core-shell nanocrystals. The nanocrystals are formed in an otherwise unreactive buff ered solution of Cd acetate and selenocystine through enzymatic turnover of the selenocystine to form a reactive precursor, likely H2Se. The particle size of the CdSe core nanocrystals can be tuned by varying the incubation time to generated particle sizes between 2.74 ± 0.63 nm and 4.78 ± 1.16 nm formed after 20 min and 24 h of incubation, respectively. Subsequent purification and introduction of L-cysteine as a sulfur source facilitates the biomineralization of a CdS shell onto the CdSe cores. The quantum yield of the resulting CdSe-CdS core-shell particles is up to 12% in the aqueous phase; comparable to that reported for more traditional chemical synthesis routes for core-shell particles of similar size with similar shell coverage. This single-enzyme route to functional nanocrystals synthesis reveals the powerful potential of biomineralization processes.

Scalable Biomineralization of CdS Quantum Dots by Immobilized Cystathionine γ-Lyase

“…Engineered and purified strains of cystathionine γ-lyase (CSE) were employed for the synthesis of CdS QDs following previous reports. ,,,,, Specifically, QD synthesis was initiated from a solution of 1 mM cadmium acetate (Alfa Aesar, 99.999% Puratronic), 7 mM l -cysteine (Spectrum Chemicals), and 0.05 mg mL –1 CSE in 0.1 M Tris-HCl (pH 8.0, VWR) buffer. The solution was incubated at 37 °C for 2 h. The concentration of QDs in the solution was computed from UV–vis absorbance measurements based upon published calibrations .…”

“…Low-temperature, aqueous phase biosynthetic routes, which rely on intracellular or extracellular enzymatic turnover of QD precursors, offer the potential for improved sustainability and satisfaction of numerous principles of green engineering owing to the use of an intrinsically “green” solvent, ambient reaction temperatures, water-soluble ligands, and the catalytic precision of enzymes. ,− Among biosynthetic approaches, environmentally benign and low-cost extracellular single-enzyme biomineralization of size-controllable QDs of a range of material compositions is possible, including CdS, CdSe, ZnS, PbS, CuInS 2 , CuZnSnS 4 , and Ag 2 S. − Specifically, pyridoxal phosphate (PLP)-dependent cystathionine γ-lyase (CSE) catalyzes the reaction of a variety of amino acid substrates, including l -cysteine, l -homocysteine, and l -cystine, leading to endogenous production of H 2 S and thus reactive HS – species. , For example, l -cysteine serves as both the sulfur source and QD capping agent for the biomineralization approach. Recent detailed quantitative assessment of the commercial viability of a number of common colloidal QD synthesis strategies for solar photovoltaics, which has carefully accounted for uncertainties in numerous processing variables, estimates that ca.…”

Enzymatic biomineralization of biocompatible CuInS2, (CuInZn)S2and CuInS2/ZnS core/shell nanocrystals for bioimaging

“…We have previously demonstrated this approach for non-biocompatible materials such as CdS and CdSe. 28,29 In this current work, we demonstrate the biomineralization of non-toxic, biocompatible CuInS2, (CuInZn)S2 and CuInS2/ZnS quantum dots for bioimaging applications.…”

Tailored Coupling of Biomineralized CdS Quantum Dots to rGO to Realize Ambient Aqueous Synthesis of a High-Performance Hydrogen Evolution Photocatalyst

“…We have previously demonstrated a single-enzyme-based aqueous route for the synthesis of a variety of quantum-confined, semiconducting nanocrystals, including CdS and the reduction of graphene oxide to rGO. − Both CdS and CdS/rGO photocatalysts, although unstable over long periods of use, have been widely studied for water splitting, providing a basis for this demonstration of the potential for bioinspired and biological synthesis. rGO is often used in chemically synthesized photocatalysts as a support that can accept photoexcited electrons from CdS to suppress charge recombination, increase exciton lifetime, and ultimately increase H 2 production rates .…”