Graphene Envelops Nanoparticles

A simple technique can swathe nanoparticles with a blanket of graphene (Nano Lett., DOI: 10.1021/nl2045952). The tiny graphene packets could carry medical imaging contrast agents, allowing the nanoparticles to enhance imaging signals while shielding tissue from their potential toxic effects. They could also deliver chemotherapy drugs to tumors, says Brown University’s Robert Hurt, who developed the new nanoparticle sacks.

Other approaches to wrap nanoparticles in graphene require chemically modifying both the particles and graphene to endow them with opposite charges, Hurt says.

Hurt and his colleagues avoided the modification steps by adapting a recently reported aerosol technique for crumpling graphene flakes into wads (ACS Nano, DOI: 10.1021/nn203115u). Using an ultrasonic nebulizer, they make a mist from an aqueous suspension of graphene oxide flakes and various nanoparticles—they tested the technique with particles of silver, organic dye molecules, and DNA. Graphene oxide flakes tend to accumulate at the droplet surface. When the droplets pass through a furnace, graphene oxide reduces to graphene. As water evaporates and the droplets shrink, the graphene flakes collapse to form sacks around a few nanoparticles. A filter captures the packets.

The technique is much easier than previous graphene wrapping methods, and gives discrete, uniformly coated particles, Hurt says. Because it relies on “physically forcing things together” rather than electrostatic attraction, he says, a much wider range of materials are amenable to wrapping.

For drug-delivery applications, the team is now trying to understand if and when the packets open and release their contents, and whether the release time can be tuned. “We know they go into cells,” says Hurt, “but will they deliver?”