Biosynthesis of cadmium sulfide nanoparticles by photosynthetic bacteria Rhodopseudomonas palustris

A simple route for the synthesis of cadmium sulfide nanoparticles by photosynthetic bacteria Rhodopseudomonas palustris has been demonstrated in this work. The cadmium sulfate solution incubated with R. palustris biomass changed to a yellow color from 48 h onward, indicating the formation of cadmium sulfide nanoparticles. The purified solution yielded the maximum absorbance peak at 425 nm due to CdS particles in the quantum size regime. Also, X-ray analysis of the purified nanoparticles confirmed the formation of cadmium sulfide. Transmission electron microscopic analysis of the samples showed a uniform distribution of nanoparticles, having an average size of 8.01 ± 0.25 nm, and its corresponding electron diffraction pattern confirmed the face-centered cubic (fcc) crystalline structure of cadmium sulfide. Furthermore, it was observed that the cysteine desulfhydrase producing S2− in the R. palustris was located in cytoplasm, and the content of cysteine desulfhydrase depending on the growth phase of cells was responsible for the formation of CdS nanocrystal, while protein secreted by the R. palustris stabilized the cadmium sulfide nanoparticles. In addition, R. palustris was able to efficiently transport CdS nanoparticles out of the cell.