Shuming Nie, Ph.D., principal investigator of the Emory-Georgia Institute of Technology CCNE, and his colleagues created their new multifunctional device using semiconductor quantum dots and iron oxide nanocrystals. The investigators embedded, or doped, the nanoparticles into the nanoscale pores in 4-micron-diameter silica beads, and then coated the microbeads with a biocompatible polymer. This polymer coating helps the microbeads dissolve in water and provides a chemically reactive surface onto which the investigators plan to attach targeting molecules.
The investigators determined that each microbead has approximately 1 million pores into which they can dope quantum dots and magnetic iron oxide beads. They also found that quantum dots fill approximately 300,000 to 400,000 of these pores, far in excess of the number needed to make the microbeads visible. As a result, the researchers note, it is possible to dope the microbeads with multiple quantum dots, each shining with a different color, and use the microbeads in multiplexed assays.
To confirm that they can use the iron oxide nanoparticles as a handle for purifying molecules attached to the microbeads, the investigators mixed microbeads doped with a red quantum dot and iron oxide nanocrystals with a second set of microbeads doped solely with green quantum dots. Exposing this mixture to a magnetic field for five minutes allowed the investigators to completely separate the two sets of microbeads. If the microbeads had contained a targeting molecule, this separation would have also purified the biomolecule or cell recognized by that targeting molecule.