Synthesis of biocompatible near infrared fluorescence Ag2S quantum dot and its application in bioimaging

Near infrared (NIR) emitting quantum dots (QDs) is a promising candidate for biomedical imaging in living tissues. However, the biomedical application of NIR QDs was not satisfactory due to their toxicity. Ag2S QDs was reported to have negligible toxicity in organisms. Therefore, the appropriate narrow bandgap and low toxicity of Ag2S QDs facilitated them to be a promising contrast agent for fluorescence imaging. Here, a low toxicity, stable and highly luminescent NIR Ag2S QDs were prepared by one-step aqueous method using 2-mercaptopropionic acid (MPA) as the coating layers. Emission wavelength of Ag2S QDs could be tuned between 780 and 950 nm. MTT assay results indicated that there was no significant biotoxicty for Ag2S QDs. These NIR QDs exhibited excellent biocompatibility in tumor cells. The cellular uptake and localization of Ag2S QDs was studied using laser confocal scanning microscopy. Ag2S QDs were effectively internalized by the cells. Therefore, Ag2S QDs, acting as a novel fluorescence probe, has promising potential in biolabeling, deep tissue imaging, diagnostics and photodynamic therapy.