Gold-Based Nanoparticles Could Serve as Biomedical 'Testbed'

Photo: Sketch of a typical gold nanoparticle

Prospective uses of gold nanoparticles, says NIST chemist Vince Hackley, include high-precision drug-delivery systems and diagnostic image enhancers. Gold is nontoxic and can be fashioned into particles in a range of sizes and shapes. By itself, gold doesn't do much biologically, but it can be "functionalized" by attaching, for instance, protein-based drugs along with targeting molecules that cluster preferentially around cancer cells. The nanoparticles are generally coated as well, to prevent them from clumping together and to avoid rapid clearance by the body's immune system.

Anil Patri of National Cancer Institute’s Nanotechnology Characterization Laboratory (NCL), the second partner of the project, notes that the coating composition, density and stability have a profound impact on the nanomaterial safety, biocompatibility (how well the nanoparticles distribute in the body), and efficacy of the delivery system. "Understanding these parameters through thorough characterization would enable the research community to design and develop better nanomaterials," he says.

To facilitate such studies, the NIST/NCL team set out to create a nanoparticle testbed—a uniform, controllable core-shell nanoparticle that could be made-to-order with precise shape and size, and to which could be attached nearly any potentially useful functionality. Researchers then could study how controlled variations fared in a biological system.

Their trial system is based on regularly shaped branching molecules called dendrons, a term derived from the Greek word for "tree." Dendron chemistry is fairly new. They're excellent for this use, because the individual dendrons are always the same size, unlike polymers, and can readily be modified to carry "payload" molecules. At the same time, the tip of the structure—the "tree's" trunk—is designed to bond easily to the surface of a gold nanoparticle.

The team made an exhaustive set of measurements so they could thoroughly describe their custom-made dendron-coated nanoparticles. "There aren't a lot of protocols around for characterizing these materials—their physical and chemical properties, stability, et cetera," Hackley says, "so, one of the things that came out of the project is a basic series of measurement protocols that we can apply to any kind of gold-based nanoparticle."; Source: National Institute of Standards and Technology (NIST)