Facile Synthesis of Near-Infrared Emissive CdS Quantum Dots for Live Cells Imaging

CdS quantum dots (QDs) have attracted extensive attention owing to their great potential in optoelectronic nanodevices and biosensors. But their poor water solubility and high cytotoxicity restrict their practical application in live cell imaging. In addition, CdS QDs usually emit blue or green fluorescence, which also have some limitations for cell imaging due to the "water window" effect. In this study, we report a novel strategy to directly synthesize water-soluble and low-cytotoxic CdS QDs with near infrared (NIR) fluorescence through confinement into BSA templates with the mediation of L-cysteine (Cys). The obtained CdS QDs emit NIR fluorescence at 730 nm when exited by 468 nm excitation light, and show good water solubility and low cell cytotoxicity, which can be directly used for live RAW cell imaging. In addition, the effects of the type of amino acids for mediations, and the ratio of both Cys/Cd and Cd/BSA on the fluorescence properties of CdS QDs have also been investigated comprehensively. The mediation of L-cysteine plays a critical role on the formation of CdS QDs emitting NIR fluorescence.