Nanotech News

November 28, 2005

Altering the Surface of Quantum Dots Improves Their Performance in Live Cell Applications

Nanoscale quantum dots are now standard tools for tracking molecules within biological systems, including live cells. But because of the way these particles are prepared to make them compatible with living systems, the particles tend to stick nonspecifically to various cells and even to DNA. This nonspecific binding reduces the sensitivity of assays that use quantum dots because it can lead to background noise that can obscure a desired optical signal when only a few quantum dots are binding specifically to its particular target. But thanks to a simple modification, researchers at Vanderbilt University have created quantum dots that exhibit very little nonspecific binding, and thus, could be used to improve the sensitivity of quantum dot-based assays.

Sandra Rosenthal, Ph.D., and her colleagues used short pieces of the biocompatible polymer poly(ethylene glycol), also known as PEG, to reduce nonspecific binding to variety of different cell types. The researchers, who discuss their work in the journal Bioconjugate Chemistry, prepared a variety of coatings for standard cadmium selenide quantum dots and determined what effect the coatings had on nonspecific binding and on the brightness of the fluorescent signal that the quantum dots could generate. Using a coating that reduced nonspecific binding at the expense of reduced signal intensity from a quantum dot would produce little overall gain in the sensitivity of an assay.

What the investigators found was that even short pieces of PEG made of only 12 to 14 units of ethylene glycol were able to reduce nonspecific binding substantially. Using short PEG as a coating had no significant effect on the ability of the quantum dots to fluoresce brightly. The researchers note that this coating should not interfere with the ability to later add targeting molecules to the surface of treated quantum dots. Such targeting molecules play an integral role in the use of quantum dots to track individual biomolecules within live cells.

This work is detailed in a paper titled, “Surface modification to reduce nonspecific binding of quantum dots in live cell assays,” and is based on work funded in part by the National Institutes of Health. This paper was published online in advance of print publication. An abstract is available at the journal’s website.
View abstract.