Controlling Blood Clotting With Gold Nanoparticles

Rebekah Eliason for – Your Universe Online
MIT researchers have developed an exciting new use for gold nanoparticles. Controlled by an infrared laser, the particles can be used to turn blood clotting on and off. This could be especially useful to doctors who are trying to control clotting during surgery and could promote faster, safer healing after surgery.
Using blood thinners is the only way doctors can currently control the body’s natural clotting mechanism. This is helpful to stop clotting, but once it is used the effects cannot be easily or quickly reversed.
Kimberly Hamad-Schifferli, technical staff member at MIT Lincoln Laboratory, explained how blood thinners, such as heparin, can turn off but not restore the body’s clotting ability. “It’s like you have a light bulb, and you can turn it on with the switch just fine, but you can’t turn it off. You have to wait for it to burn out,” she said.
In order for blood clotting to occur, long strands of protein work together to form fibrin which is a protein that helps seal wounds. Blood thinners stop clotting by targeting various key reactions in proteins during clotting. Hamad-Schifferli explained a better solution would be to target only the last step of converting fibrinogen to fibrin, which is regulated by the enzyme thrombin.
In a previous study, researchers found a specific sequence of DNA prevents thrombin from causing clotting by binding to it in place of fibrinogen. A complementary DNA sequence can stop the inhibition by binding to the strand of original DNA preventing interactions with thrombin.
Previously, Hamad-Shifferli and her team showed how gold nanorods can release drugs or other compounds when activated by infrared light. The specific wavelength of light necessary to activate the rods is dependent on the size of the rod. Consequently, two different lengths of rods could carry two types of compounds and be independently controlled.
To control clotting in this study, a small 35 nanometer-long rod was loaded with the DNA thrombin inhibitor and a larger 60 nanometer rod was filled with the complementary DNA strand. To start with, researchers tried to bond the DNA directly with the rod, but not enough could be loaded to be effective.
Hamad-Schifferli said, “We realized we could use a bad side effect of nanoparticle biology to our advantage.” This is the tendency of particles to attract an encompassing amount of proteins that bind to gold and make it sticky. “If you do that, you can get way more drug on the nanorod than you normally would if you had to chemically link them together,” she explained.
As the gold nanorods are exposed to specific infrared light wavelengths, the electrons in the gold become excited and release enough heat to slightly melt the gold. The change in shape causes the rod to become slightly spherical and release the DNA.
Samples of blood were provided from hospital donations. Researchers discovered they were able to turn clotting on and off at will in all of the samples.
Luke Lee, professor of bioengineering, said, “It’s really a fascinating idea that you can control blood clotting not just one way but by having two different optical antennae to create two-way control. It’s an innovative and creative way to interface with biological systems.”
In order for the particles to be useful for patients, they would need to target the specific site of the injury. Additionally, the particles must be within a few millimeters of the skin in order for the infrared light to activate them. In addition, researchers are working to alter the system so a smaller, less powerful continuous wave laser can be used to activate the particles.
A report of this study appears in the July 24 issue of the journal PLOS ONE, and the research was funded by the National Science Foundation.

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