Engineering new uses for gold

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.

Source: MIT

Related stories:

Turbocharged Nanomotors
(PhysOrg.com) -- Nanorobots that are introduced into the body to eradicate tumor cells or clean out clogged arteries are not just science fiction; they are a realistic vision of the technological possibilities of the not-so-distant future. Efficient nanomotors will be needed to drive these nanomachines.
Gold Nanostars Outshine the Competition
(PhysOrg.com) -- Novel nanoparticles being tested at the National Institute of Standards and Technology have researchers seeing stars. In a recent paper,* NIST scientists used surface-enhanced Raman spectroscopy (SERS) to demonstrate that gold nanostars exhibit optical qualities that make them superior for chemical and biological sensing and imaging. These uniquely shaped nanoparticles may one day be used in a range of applications from disease diagnostics to contraband identification.
Teaching Nano to Swim
(PhysOrg.com) -- Ayusman Sen, head of the Department of Chemistry at Penn State, makes tiny, metallic objects do something extraordinary -- he makes them swim. Sen's work is driven by catalysis, the chemical phenomenon whereby a substance accelerates a chemical reaction but emerges unchanged at the end of the process.
Purifying nanorods: Big success with tiny cleanup
Chemists at Rice University have discovered a novel method to produce ultra-pure gold nanorods -- tiny, wand-like nanoparticles that are being studied in dozens of labs worldwide for applications as broad as diagnosing disease and improving electronic viewscreens.
Golden Nanorods for Medical Applications
(PhysOrg.com) -- Gold nanoparticles are under consideration for a number of biomedical applications, such as tumor treatment. A German-American research team at Carnegie Mellon University in Pittsburgh, Hunter College in New York, and the RWTH Aachen has now developed a new method for the production of nanoscopic gold rods. In contrast to previous methods, they have achieved this without the use of cytotoxic additives. As they report in the journal Angewandte Chemie, the synthesis is not carried out in water, but in an ionic liquid, a “liquid salt”.
Biosensing nanodevice to revolutionize health screenings
One day soon a biosensing nanodevice developed by Arizona State University researcher Wayne Frasch may eliminate long lines at airport security checkpoints and revolutionize health screenings for diseases like anthrax, cancer and antibiotic resistant Staphylococcus aureus (MRSA).
Nanodisk Codes
Researchers at Northwestern University have devised a way to use billionth-of-a-meter-sized disks to create codes that could be used to encrypt information, serve as biological labels, and even tag and track goods and personnel.
'Golden bullet' shows promise for killing common parasite
Researchers in Australia report development of a new type of gold nanoparticle that destroys the parasite responsible for toxoplasmosis, a potentially serious disease acquired by handling the feces of infected cats or eating undercooked meat. Their so-called “golden bullet” could provide a safer, more effective alternative for treating the disease than conventional drug therapy, they say. The study is scheduled for the Dec. issue of ACS’ Nano Letters, a monthly journal.

News discussion:

Physics news