Quantum dots, used increasingly as bright fluorescent markers in basic research and diagnostic assays, must be coated, or capped, with one of a wide variety of organic molecules in order to stabilize these nanocrystals and prevent them from aggregating when added to water. Once coated, researchers then add a targeting agent, such as an antibody or aptamer, that enables the quantum dot to bind tightly to a biomolecule of interest.
Michael Strano, Ph.D., and colleagues at the University of Illinois have a discovered that they can combine capping and targeting in a simple step, producing water-soluble lead sulfide (PbS) quantum dots that emit bright near-infrared light. The key discovery, described in a paper published in the Journal of the American Chemical Society, was that aptamers – short stretches of synthetic DNA that have many of the binding properties of antibodies – can function as both a capping agent and a targeting agent.
Aptamer-capped quantum dots, which the researchers create at room temperature in open air, remain stable for months and have diameters ranging from 3 to 6 nanometers. Tests with these coated nanocrystals showed that they bind to their targets within one minute and can detect proteins at concentrations as low as 1 nanomolar.
This work is detailed in a paper titled, “Aptamer-capped nanocrystal quantum dots: a new method for label-free protein detection.” An abstract of this paper is available through PubMed.