Coated Ultrasmall Quantum Dots Suitable for In Vivo Imaging

Dec 03, 2007

Quantum dots have shown promise in a variety of imaging and therapeutic applications, particularly when they are coated to render them biocompatible. However, such coating can increase the size of quantum dots signficantly, which can adversely effect their pharmacokinetic and biodistribution properties.

Now, researchers at the Massachussetts Institute of Technology and Beth Israel Deaconess Medical Center have developed a new procedure that produces ultracompact quantum dots. Tests with these new materials show that this coating not only does not impair the superior optical properties of the quantum dots but also improves how the quantum dots behave in living animals.

Moungi Bawendi, Ph.D., a member of the MIT-Harvard Center of Cancer Nanotechnology Excellence, and John Frangioni, M.D., Ph.D., led this study. Their results appear in the Journal of the American Chemical Society.

To create these compact quantum dots, the investigators first create dual-layer nanocrystals that have a zinc-cadmium-sulfide (ZnCdS) core surrounded by a cadmium selenide (CdSe) shell. This combination of materials creates a compact yet bright quantum dot. Next, the researchers add a coating of cysteine, a sulfur-containing amino acid that binds tightly to the CdSe shell.

When stored in the presence of a reducing agent, these quantum dots are stable for 1 week at room temperature and at least 3 months at 4°C. Dynamic light scattering, a technique used to study nanoparticle size, showed that the diameter of these quantum dots was 5.9 nanometers. More importantly, their size did not increase when incubated with serum, demonstrating that the cysteine coating prevented proteins from collecting on the quantum dot surface.

The researchers note that the exceptionally small size of their quantum dots and their stability in serum led to new in vivo behavior. When injected into rats, the majority of the quantum dots accumulated in the bladder within 4 hours, demonstrating that these nanoparticles are small enough to be filtered out of the kidneys. In practical terms, this finding suggests that these compact quantum dots, if attached to a small targeting molecule, could be used to image tumors without having to worry about accumulation within the body. Any injected dose that did not bind to its target would clear rapidly, decreasing background noise and improving the sensitivity of tumor imaging.

This work, which was supported in part by the National Cancer Institute’s Alliance for Nanotechnology in Cancer, is detailed in the paper "Compact cysteine-coated CdSe(ZnCdS) quantum dots for in vivo applications." This paper was published online in advance of print publication. An abstract of this paper is available through PubMed.

Source: National Cancer Institute

Explore further: Chemists design nanoparticles that can deliver three cancer drugs at a time

add to favorites email to friend print save as pdf

Related Stories

Alan Guth on new insights into the 'Big Bang'

Mar 20, 2014

Earlier this week, scientists announced that a telescope observing faint echoes of the so-called "Big Bang" had found evidence of the universe's nearly instantaneous expansion from a mere dot into a dense ...

Bright future for protein nanoprobes

Mar 18, 2014

(Phys.org) —The term a "brighter future" might be a cliché, but in the case of ultra-small probes for lighting up individual proteins, it is now most appropriate. Researchers at the U.S. Department of ...

Recommended for you

User comments : 0

More news stories

Making 'bucky-balls' in spin-out's sights

(Phys.org) —A new Oxford spin-out firm is targeting the difficult challenge of manufacturing fullerenes, known as 'bucky-balls' because of their spherical shape, a type of carbon nanomaterial which, like ...

Melting during cooling period

(Phys.org) —A University of Maine research team says stratification of the North Atlantic Ocean contributed to summer warming and glacial melting in Scotland during the period recognized for abrupt cooling ...