Using designer proteins to make quantum dots

In a unique marriage of synthetic biology and chemistry, researchers have used custom-made proteins to drive chemical reactions that produce cadmium sulfide quantum dots (Proc. Natl. Acad. Sci. 2022, DOI: 10.1073/pnas.2204050119). Quantum dots are semiconductor nanocrystals that shine in a range of bright, pure colors depending on their size.

The cheapest way to make quantum dots today requires high temperatures and organic solvents. The new protein-catalyzed process works in aqueous solution at room temperature and produces high-quality quantum dots 2–5 nm in size.

Chemists Michael Hecht, Gregory Scholes, and Sarangan Chari of Princeton University and their colleagues started with a designer protein made previously in their lab (Protein Sci. 2016, DOI: 10.1002/pro.2871). They discovered recently that this protein can catalyze the removal of sulfur from the amino acid cysteine to form hydrogen sulfide.

The team added in cadmium chloride and found that it reacts with the H₂S to form CdS quantum dots. The reaction proceeds slowly, growing nanocrystals in a controlled manner, creating uniformly sized dots with optical properties matching that of conventionally produced ones. Longer reaction time led to larger nanocrystals.

This method to make quantum dots could open up new uses for the nanomaterial as biosensors and also lays the foundation for designing “made-from-scratch” proteins that perform chemical functions, Hecht says.