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,"
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
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.