Biogenic design of ZnS quantum dots - Insights into their in-vitro cytotoxicity, photocatalysis and biosensing properties

Abstract Zinc sulphide Quantum Dots (QDs) are semiconductor nanoparticles that have profound applications in medical imaging, photocatalysis and biosensing. Of late, green synthesis of ZnS QDs has emerged as an useful substitute for the routine chemical synthesis. The present study reports the biosynthesis of ZnS QDs using the fungus Aspergillus sp. under ambient conditions. In the present study, the mechanism behind the antibacterial action of the biosynthesized ZnS Quantum Dots has been explored. It was found that biogenesis using fungus has resulted in the synthesis of spherical crystalline ZnS particles of mean diameter 6.3 nm. FTIR analysis indicated the presence of active organic functional groups on the surface of the QDs. The optical and structural features of the biogenic ZnS were found to be comparable with that of the chemically synthesized quantum dots. Thereafter, the antibacterial activities of the biosynthesized ZnS QDs were observed against pathogenic bacteria. The green synthesized ZnS exhibited excellent antibacterial activity and were quantified using filter paper bioassay. Experimental evidences indicated that the antibacterial strategy relied on bacterial cell membrane disruption, leakage of the cytoplasmic contents and associated ROS mediated oxidative damages leading to bacterial cell lysis. Further, the prospects of biogenic ZnS for photodegradation of dyes and sensing of heavy metals in aqueous phase were investigated.