Characterization of CdSe QDs biosynthesized by a recombinant Rhodopseudomonas palustris

This study proposed a novel approach for the biosynthesis of CdSe quantum dots (QDs) by a recombinant photosynthetic bacteria Rhodopseudomonas palustris with metallothionein expression. The biosynthesis mechanisms and physico-chemical properties of the CdSe QDs were analyzed by various techniques, and its potential application was also investigated. The results showed that the biosynthesized CdSe QDs presented green fluorescence with maximum excitation and emission wavelengths at 460 and 530 nm, respectively. The quantum yield of the biosynthesized CdSe QDs was found out to be 3.85%. They were well-dispersed spherical particles with an average size of 5.37 ± 0.06 nm. Their crystal structure was cubic with the d spacings of 3.1 Å and 2.5 Å, corresponded to the planes of (111) and (220), respectively. The biosynthesis process of CdSe QDs took place in the cytoplasm and may involve some proteins, peptides, lipids or other organic substances covering the surface of CdSe QDs through several specific functional groups, such as hydroxyl or sulfhydryl groups to maintain their stability. The purified CdSe QDs had good biocompatibility and great potential for cellular imaging application. It is concluded that the process may provide a more cost-effective and eco-friendly method not only to recover harmful cadmium in the environment but also to synthesize simultaneously a clean product for various industrial applications.