Selective targeting of cellular nucleus using positively-charged quantum dots.

Developing highly selective probes for subcellular regions such as nucleus and cytoplamic organelles is of great interest for cellular imaging and high content screening analysis for biology and medicine. Cytoplasmic delivery of QDs has been well-understood, while nuclear delivery of QDs has been a challenge due to the unique structural characteristics of cell nucleus. In this study, we systematically investigated nucleus penetrating properties of small-sized ligand-exchanged QDs with either positive or negative surface charges in the similar size range of hydrodynamic diameter (7-10 nm). We found that the positively-charged QDs efficiently stain the nucleus in fixed HeLa cells as well as label nucleolar compartments in live HeLa cells. In contrast, the negatively charged QDs with the similar size range stain only the cytoplam in either fixed or live cells. The charge-dependent labeling pattern allowed us to simultaneously perform multiplex imaging of nuclues and cytoplasm. This study offers an insight into efficient nuclear delivery of nanoparticles such as QDs of which surface charge and size are critical for intracelllar localization and delivery.