Fantastic Voyage - Nanotechnology

"This is an important problem," Leary says. "If humans are going to live in space, we have to figure out how to protect them from radiation better."

Because shielding alone probably won't solve the problem, scientists must find some way to make the astronauts themselves more resistant to radiation damage.

Nanoparticles offer an elegant solution. These drug-delivery capsules are tiny - only a few hundred nanometers, which is smaller than a bacterium and smaller even than the wavelengths of visible light. (A nanometer is one-millionth of a millimeter.)

A simple injection with a hypodermic needle can release thousands or millions of these capsules into a person's bloodstream. Once there, nanoparticles will take advantage of the body's natural cellular signaling system to find radiation-damaged cells.

The trillions of cells in a human body identify themselves and communicate with each other via complex molecules embedded in their outer membranes. These molecules act as chemical "flags" for communicating to other cells or as chemical "gates" that control entrance to the cell for molecules in the bloodstream (such as hormones).

Image copyright Scott Barrows, University of Illinois at Chicago. A two-layered membrane separates the cell interior in the bottom-right of this image from the surrounding environment. Complex molecules in this outer membrane control how the underlying cell interacts with its surroundings.

When cells become damaged by radiation, they produce markers in a particular class of proteins called "CD-95" and place these on their outer surfaces.

"It's how the cell speaks to other cells and says, 'Hey, I'm injured,'" Leary says.

By implanting molecules in the outer surface of the nanoparticles that bind to these CD-95 markers, scientists can "program" the nanoparticles to seek out these radiation-damaged cells.

If the radiation damage is very bad, nanoparticles can enter the damaged cells and release enzymes that initiate the cell's "auto-destruct sequence," known as apoptosis. Otherwise, they can release DNA-repair enzymes to try to fix the cell and return it to normal functioning.

Humans and other organisms have natural enzymes that tend to DNA and repair mistakes, but some do a better job than others. "There are organisms that can [absorb high] radiation doses and do just fine," Leary says. By studying such species, scientists have already fashioned DNA-repairing enzymes that could be delivered by nanoparticles.

Leary's team is also studying ways to attach fluorescent molecules to the nanoparticles. These could be designed to light up at certain stages of the process, even employing different colors for different stages. These fluorescent tags would provide a way to monitor the nanoparticles within the body.