The facile one-step aqueous synthesis of near-infrared emitting Cu+ doped CdS quantum dots as fluorescence bioimaging probes with high quantum yield and low cytotoxicity

In the past two decades, Cu-doped inorganic semiconductors with near-infrared (NIR) emitting have garnered stupendous research interest. Nevertheless, the incompatibility between the NIR emitting and high photoluminescence quantum yield (PLQY) of the Cu-doped fluorescent probes restricted the extensive application in biological imaging. Herein, the water soluble Cu+ doped CdS quantum dots (Cu+:CdS QDs) were prepared by using a one step synthesis method in a N2 atmosphere. The d-dots possessed an ultra small size (∼5 nm), a high QY (25.6%), NIR emission (∼700 nm) and a low cytotoxicity because of which they were used as fluorescence probes. Besides, the study of the Cu d state and the mechanism of emission proposed the explanation for the fluorescence enhancement compared with previous reports. Moreover, the optimal conditions of dopants, stabilizers, sulfur ion concentration, pH, heating time and reflux temperature were also studied systematically to acquire best-quality Cu-doped nanocrystals. Due to the excellent optical properties and favourable biocompatibility, the Cu+:CdS QDs as fluorescence probes were successfully applied to label living 3T3 cells.