This study addresses the cellular uptake of nanomaterials in the field of bio-applications. In the present study, we have synthesized water-soluble lead sulfide quantum dot (PbS QD) with glutathione and 3-MPA (mercaptopropionic acid) as the stabilizing ligand using a green approach. 3-MPA-capped QDs were further modified with streptavidin and then bound to biotin because of its high conjugation efficiency. Labelling and bio-imaging of cells with these bio-conjugated QDs were evaluated. The bright red fluorescence from these types of QDs in HeLa cells makes these materials suitable for deep tissue imaging.