Quantum dots are powerful multipurpose vital labeling agents in zebrafish embryos.

Recently, inorganic fluorescent contrast agents composed of semiconductor materials have been introduced to biological imaging approaches. These so-called quantum dots provide unique and promising properties unreached by organic fluorophores, but their use as contrast agents within live organisms has been limited, probably due in part to concerns about their in vivo tolerance. Using transparent zebrafish embryos, we challenged quantum dots with a series of intravital imaging problems. We show that quantum dots provide a high fluorescent yield within targeted tissues, possess immense photostability, can be targeted to specific subcellular compartments, remain within targeted cells as lineage tracers, are easily separable from conventional organic fluorescent dyes, and are fixable, allowing them to be used in combination with immunohistochemistry after live recordings. Thus, quantum dots combine the specific advantages of different organic fluorescent contrast agents and promise to become the first fluorophore feasible for long-lasting intravital time-lapse studies. Finally, we show by co-labeling blood vessels of the vasculature and major axon tracts of the nervous system that, for establishing these networks, the same guidance cues might be used in some body parts, whereas in others, both networks appear to develop independently from one another. Thus, the bright fluorescence of quantum dots will help to unravel many open questions in the fields of embryology, cell biology, as well as phenotyping and disease diagnosis.