Researchers at Lehigh University led by Tori Berard have devised a process in which bacteria produces cadmium sulfide nanocrystals (quantum dots). While the optical properties of quantum dots (QDs) have made them attractive for photovoltaics, lighting, display, and biomedical imaging technologies, the cost to produce them has been prohibitive. Additionally, the process to chemically synthesize them requires high pressures, high temperatures, and toxic solvents. Thus, electronics manufacturers need a scalable, cost-effective, and more environmentally friendly quantum dot synthesis process.
The researchers have described the directed evolution of a gram-negative bacteria, Stenotrophomonas maltophilia for the production of cadmium sulfide (CdS) nanocrystals (QDs) directly from cell culture. The biosynthesis procedure they devised can produce the nanocrystals at low temperatures and pressures. They point out that the required high temperatures and pressures of conventional chemical synthesis processes in addition to the handling and cleanup of toxic solvents add tremendously to the process cost of $1000-$10000 per gram. They claim that with their biosynthesis process, purification and recovery of soluble QD product might be possible at a cost as low as $10-$100/g.
They employed gram-negative bacteria that is highly resistant to toxic metals. The bacteria performed iterative growth in the presence of aqueous cadmium acetate. Selected strains exhibited high (> 10 mM) tolerance to aqueous cadmium salt solutions. CdS particles have an absorbance peak at 348 nm that correlates to 2.03 nm diameter and emits green under UV light.
The researchers speculated, “If we were able to produce these particles efficiently, inexpensively, and on a large scale, we could potentially produce QDs at a scale and cost compatible with commercial applications such as photovoltaics and biomedical imaging, and do so with little environmental impact.”
The researchers hope to develop a recipe to produce soluble CdS quantum dots outside of the bacteria.