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Quantum dot: a promising new imaging agent

​The drawback to current optical imaging markers is their short life. Researchers are now developing fluorescent nanocrystals (quantum dots) to supplant these markers. A team from the CEA-iBiTec-S, in collaboration with the CEA-I2BM and ESPCI [1], has developed a new surface chemistry for these particularly effective nanoparticles.

Published on 22 March 2013

The use of organic fluorophores [2] as imaging agents represents an alternative to radioactive isotopes. However, these fluorophores bleach quickly in light (sometimes within seconds), becoming imperceptible. Quantum dots (QD), crystals on the nanometer scale, could become the next generation in imaging agents: they have remarkable fluorescence properties and remain operational for one to several hours. They are comprised of a mixed metal core (e.g. indium, copper, etc.), surrounded by one or more layers of biocompatible surfaces that allow an in vivo administration. However, this covering is often lost in practice. As a result, QD become poorly soluble and thus less mobile; this promotes their aggregation, reducing their effectiveness and increasing the risk of toxicity.







Left, a schematic representation of a quantum dot. Right, the biodistribution of quantum dots in the circulatory system of a mouse


Researchers from the CEA-iBiTec-S developed another biocompatible covering that is particularly effective. This new single-layer system is securely anchored to the surface of the metal core. In addition, chains of polyethylene glycol molecules make these nanocrystals “stealthy”, i.e.invisible to the body's defenses. This last feature allows them to navigate through the blood without being destroyed by the immune system. The first whole-body images of a mouse were obtained, allowing visualization of the entire circulatory system. The researchers verified that the QD do not preferentially accumulate in organs. Ultimately, they transit through the liver, suggesting elimination by natural means. In view of these results, researchers can consider a broader use of this type of coating for the biocompatibilization of various nanoparticulate systems.

[1] Ecole supérieure de physique et de chimie industrielles de la ville de Paris.
[2] A chemical substance capable of emitting fluorescent light upon excitation.

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