Probing the bacterial detoxification of cadmium to form cadmium sulfide quantum dots and the underlying mechanism

Microbe-reinforced mineralization of metals into biocompatible materials is a potential drive towards the green synthesis of materials. However, metal biomodification into nanoparticles verily exhibits non-uniformity of the nanoparticles due to limited study of the cell behavior and bio-mechanism, which mitigate their applications in the optoelectronics field. In the present study, we utilized the self-assembly behaviour of chemical species in a biological environment to produce mono-disperse and well-controlled cadmium sulfide quantum dots (CdS QDs). Cadmium quenching (up to 85%) by organic molecules, exported from bacterial (Pseudomonas aeruginosa) cells, has been established by studying the influence of biological growth parameters (cell age) and precursors (cysteine and cadmium) on the formation of CdS QDs. Herein, we elucidate the mechanism involved in the bacterial precipitation of cadmium into CdS QDs using AFM and TEM profiles, which confirm the hypothesis of QD formation involving the cell wall in the medium and its interaction with precursors. The green synthesis of CdS QDs with controllable surface functionalities (studied via FTIR spectroscopy) results in tunable photoluminescence.