Credit: © 2007 ACS

Fluorescent structures, such as quantum dots (QDs), are useful for tracking cells in studies of their biochemical behaviour. Many types of labels exist, but few can disperse in cells uniformly or are suitable for all cell types. Now, researchers at Carnegie Mellon University in the US have used a protein-based toxin to label cells with QDs more effectively.

Byron Ballou and colleagues1 linked one of the protein subunits of cholera toxin — a molecule that binds to surfaces of most mammalian cells — onto different QDs and used them to label five cell types including human and mouse stem cells. The QD conjugates were internalized by the cells into small vesicles that were completely dispersed throughout the cytoplasm. Labelled stem cells could still transform into different lineages when placed in a suitable environment, suggesting that the conjugates did not interfere with normal cell behaviour. When compared with QDs coated with a polymer made from the amino acid arginine, the labelling was found to be more uniform and it remained in the cells over several generations of cell division with no obvious toxic effects.

These QD–molecule hybrids can easily label a wide variety of cell types and are suited for long-term cell tracking studies because they are stable in the presence or absence of serum, do not aggregate and can achieve uniform labelling.