Bioluminescent quantum dots

RESEARCH HIGHLIGHTSBioluminescent quantum dotsBioluminescence is widely used for in vivo

imaging of nude mice. By conjugating

luciferase protein to quantum dots, bioluminescence resonance energy transfer

(BRET) turns these useful fluorophores

into a new class of bioluminescent probe.Quantum dots have several advantageous

characteristics that have made them the fluorophore of choice in many applications.

Unfortunately they are not particularly

suited to whole-animal in vivo imaging,

an application that is becoming increasingly popular. Now Jianghong Rao, Sanjiv

Gambhir and colleagues from the Molecular

Imaging and Bio-X Program for interdisciplinary research at Stanford describe the

synthesis and the use of bioluminescent

quantum dots for in vivo imaging.Although quantum dots can emit light

in the red and infrared regions of the spectrum that have good tissue penetration,

they all require blue light for efficient excitation. Blue light, however, does not penetrate tissue well and also produces high

background owing to excitation of endogenous fluorophores. During in vivo imaging, this results in low excitation efficiency

and high background. Rao and colleagues

thought there must be a way to solve this

problem.Rao says they decided to try using

luminescent light to excite quantum

dots. This light can come from a bioluminescent protein that produces light

via a chemical reaction. We tried firefly luciferase first, and it was very hard

to do the conjugation, says Rao. The

reason was probably that the firefly

luciferase is very fragile and sensitive to any

chemical modification. This caused it to

dramatically loose its luciferase activity.The Gambhir laboratory has been developing methods to use BRET imaging in