Metal-based quantum dots: synthesis, surface modification, transport and fate in aquatic environments and toxicity to microorganisms

Semiconductor quantum dots (QDs) have attracted considerable attention for their superior optical properties and wide utilization in biological and biomedical studies. Recently, intense concerns have been focused on the cytotoxicity assessment of QDs because most QDs are made of heavy metal ions (e.g., Cd2+), which pose a threat to human beings and simultaneously hamper the practical applications of QDs. This review provides an overview of the synthetic methods, surface modification, dissolution mechanism and cytotoxicity of core-shell QDs. Accordingly, the effects of polymer coating materials and environmental conditions on the dissolution kinetics of polymer-coated core-shell QDs are discussed in detail. To offer a systematic analysis of the cytotoxicity of QDs to microorganisms, correlative factors such as particle size, surface coating materials, photolysis and oxidation, charge, concentration, exposure time and mechanical stability are taken into consideration with respect to the mechanism of their toxicity. Future research will concentrate on toxicological and pharmacological studies of QDs to find new strategies with lower risk and higher benefits for public health, providing a unique technique for nanopharmaceutical applications.