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. ₂ QDs was reported to have negligible toxicity in organisms. Therefore, the appropriate narrow bandgap and low toxicity of ₂ QDs facilitated them to be a promising contrast agent for fluorescence imaging. Here, a low toxicity, stable and highly luminescent NIR ₂ QDs were prepared by one-step aqueous method using 2-mercaptopropionic acid (MPA) as the coating layers. Emission wavelength of ₂ QDs could be tuned between 780 and 950 nm. MTT assay results indicated that there was no significant biotoxicty for ₂ QDs. These NIR QDs exhibited excellent biocompatibility in tumor cells. The cellular uptake and localization of ₂ QDs was studied using laser confocal scanning microscopy. ₂ QDs were effectively internalized by the cells. Therefore, ₂ QDs, acting as a novel fluorescence probe, has promising potential in biolabeling, deep tissue imaging, diagnostics and photodynamic therapy.