Light Deactivates Anthrax

A new technique targets specific proteins, such as the dangerous anthrax toxin, and renders them harmless using nothing but light. The method could also be used to create new cancer treatments and antibacterial coatings.

Scientists have long been interested in wrapping proteins around carbon nanotubes, and the process is used for various applications in imaging, biosensing, and cellular delivery. But this new study at Rensselaer Polytechnic Institute (RPI) is the first to remotely control the activity of these conjugated nanotubes.

A team of RPI researchers led by Ravi S. Kane, professor of chemical and biological engineering, has worked for nearly a year to develop a means to remotely deactivate protein-wrapped carbon nanotubes by exposing them to invisible and near-infrared light. The group demonstrated this method by successfully deactivating anthrax toxin and other proteins.

Transmission electron microscope images show carbon nanotubes conjugated with anthrax toxin before (a, b) and after (c, d) exposure to ultraviolet light. This light caused the absorbed toxin to deactivate and fall off the nanotube, which is why the structures in pictures c and d are smaller in diameter than those in pictures a and b. (Images courtesy Rensselaer/Ravi Kane)

“By attaching peptides to carbon nanotubes, we gave them the ability to selectively recognize a protein of interest -- in this case anthrax toxin -- from a mixture of different proteins,” Kane said. “Then, by exposing the mixture to light, we could selectively deactivate this protein without disturbing the other proteins in the mixture.”

By conjugating carbon nanotubes with different peptides, this process can be easily tailored to work on other harmful proteins, Kane said. Also, employing different wavelengths of light that can pass harmlessly through the human body, the remote control process will also be able to target and deactivate specific proteins or toxins in the human body. Shining light on the conjugated carbon nanotubes creates free radicals, called reactive oxygen species. It was the presence of radicals, Kane said, that deactivated the proteins.

Kane’s new method for selective nanotube-assisted protein deactivation could be used in defense, homeland security, and laboratory settings to destroy toxins and pathogens. The method could also offer a new method for the targeted destruction of tumor cells. By conjugating carbon nanotubes with peptides engineered to seek out specific cancer cells, and then releasing those nanotubes into a patient, doctors may be able to prevent the spread of cancer.

Kane’s team also developed a thin, clear film made of carbon nanotubes that employs this technology. This self-cleaning film may be fashioned into a coating that, at the flip of a light switch, could help prevent the spread of dangerous bacteria, toxins, and microbes.

“The ability of these coatings to generate reactive oxygen species upon exposure to light might allow these coatings to kill any bacteria that have attached to them,” Kane said. “You could use these transparent coatings on countertops, doorknobs, in hospitals or airplanes -- essentially any surface, inside or outside, that might be exposed to harmful contaminants.”

Kane said he and his team will continue to hone the technology and further explore its potential applications.

Details of the project are outlined in an article in the December issue of Nature Nanotechnology. Co-authors of the paper include Department of Chemical and Biological Engineering graduate students Amit Joshi and Shyam Sundhar Bale, postdoctoral researcher Supriya Punyani, Rensselaer Nanotechnology Center Laboratory Manager Hoichang Yang and professor Theodorian Borca-Tasciuc of the Department of Mechanical, Aerospace, and Nuclear Engineering.

The group has filed a patent disclosure for the technology. The project was funded by the National Institutes of Health and the National Science Foundation.

For more information, visit: www.rpi.edu