[Editors] Beyond jewelry: MIT engineers new uses for gold

[Teresa Herbert]

FOR IMMEDIATE RELEASE
Contact: Teresa Herbert, MIT News Office
T. 617-258-5403, E. therbert at mit.edu

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Beyond jewelry: Engineering new uses for gold
--MIT researchers see precious metal’s value in war on cancer, other  
applications
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CAMBRIDGE, Mass. -- The glitter of gold may hold more than just  
beauty, or so says a team of MIT researchers that is working on ways  
to use tiny gold rods to fight cancer, deliver drugs and more.

But before gold nanorods can live up to their potential, scientists  
must figure out how to overcome one major difficulty: The surfaces of  
the tiny particles are coated with an uncooperative molecule (a  
byproduct of the synthesis process) that prevents researchers from  
creating nanorods with the features they want.

“The surface chemistry is really key to everything,” said Kimberly  
Hamad-Schifferli, assistant professor of biological and mechanical  
engineering at MIT. “For all of these nifty applications to work,  
someone’s got to sit down and do the dirty work of understanding the  
surface.”

Hamad-Schifferli and her colleagues published two papers this month  
describing ways to manipulate the nanorods’ surface, which could allow  
researchers to design nanorods with specific useful functions.

As their name implies, gold nanorods are tiny cylinders of gold, about  
10 billionths of a meter wide and 40 billionths of a meter long.

They differ from traditional, spherical gold nanoparticles in one very  
important respect — they can absorb infrared light. That means they  
can theoretically be activated by infrared laser without damaging  
surrounding cells, which do not absorb infrared light.

Before that can happen, scientists must figure out how to deal with an  
organic molecule known as CTAB that coats the outer surface of gold  
nanorods and tends to detach from and reattach itself to the surface.  
The molecule, a byproduct of the synthesis reaction that produces the  
nanorods, makes it difficult to attach other molecules for delivery,  
such as drugs or DNA.

The team’s two recent two papers describe how the CTAB influences heat  
dissipation and how to remove the CTAB and replace it with another  
organic molecule.

In the first paper, published online Aug. 12 in the Journal of  
Physical Chemistry C, they found that a low concentration of the CTAB  
in the surrounding accelerates heat dissipation after the nanorod is  
hit with infrared light. When the concentration of CTAB is high, heat  
is dissipated more slowly.

That information could help scientists design nanorods that fight  
cancer agents by burning away tumor cells when activated with infrared  
light.

In the second paper, published online Aug. 22 in the journal Langmuir,  
the team demonstrated how to replace CTAB with a more useful molecule  
— a sulfur-containing group known as a thiol. This molecule binds more  
strongly to the nanorod, so it doesn’t detach and reattach like CTAB.  
In addition, other molecules, such as DNA, can be easily attached to  
the end of the thiol.

These surface chemistry studies are critical to lay the groundwork for  
development of gold nanorods, according to Hamad-Schifferli.

“People have dreamed up all of these cool applications for nanorods,  
but one of the biggest bottlenecks to making this a reality is this  
interface,” she said.

In the future, Hamad-Schifferli and her colleagues hope to build gold  
nanorods that carry DNA designed for a specific function in the target  
cell. For example, the DNA could shut down production of a protein  
that is being overexpressed.

Lead author of the Langmuir paper is Andy Wijaya, a graduate student  
in chemical engineering.

Lead authors of the JPCC paper are Aaron Schmidt, a postdoctoral  
associate in mechanical engineering, and Joshua Alper, a graduate  
student in mechanical engineering. Other authors are Matteo Chiesa, a  
visiting scholar in the Technology and Development Program, Gang Chen,  
the Rohsenow Professor of Mechanical Engineering, and Sarit Das, a  
visiting professor in mechanical engineering.

The work was funded by the Norwegian Research Council, the Ford-MIT
Alliance and the National Science Foundation.

By Anne Trafton, MIT News Office

# # #

Teresa Herbert
Media Specialist
Massachusetts Institute of Technology
News Office, Room 11-400
Cambridge, MA 02139-4307

Phone: 617-258-5403
Fax: 617-258-8762

therbert at mit.edu




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