Extracellular microbial synthesis of biocompatible CdTe quantum dots

An efficient bacterial synthesis method to harvest cadmium telluride (CdTe) quantum dots (QDs) with tunable fluorescence emission using Escherichia coli is demonstrated. Ultraviolet–visible, photoluminescence, X-ray diffraction and transmission electron microscopy analysis confirmed the superior size-tunable optical properties, with fluorescence emission from 488 to 551 nm, and the good crystallinity of the as synthesized QDs. A surface protein capping layer was confirmed by hydrodynamic size, ζ potential and Fourier transform infrared spectroscopy measurements, which could maintain the viability (92.9%) of cells in an environment with a QD concentration as high as 2 μM. After functionalization with folic acid the QDs were used to image cultured cervical cancer cells in vitro. Investigations of bacterial growth and morphology and the biosynthesis of CdTe QDs in Luria–Bertani medium containing E. coli-secreted proteins showed that extracellular synthesis directly relied on the E. coli-secreted proteins, and a mechanism for protein-assisted biosynthesis of QDs is proposed. This work provides an economical approach to fabricate highly fluorescent biocompatible CdTe QDs via an environmentally friendly production process. The biosynthesized QDs may have great potential in broad bio-imaging and bio-labeling applications.