SAN FRANCISCO, Sept. 25 (Xinhua) -- The laboratory of Jennifer Dionne, associate professor of materials science and engineering at Stanford University, is developing an optical filter to sort out mirrored molecules.
Many molecules made in labs are chiral, which means they have an asymmetrical structure. When scientists synthesize a chiral molecule, they often make its doppelganger, a mirror image of the intended molecule. The two may look similar but, like the right and left hand, they are not interchangeable.
"Approximately 50 percent of drugs and 30 percent of agrichemicals are chiral, which means they can be left- or right-handed. Of those, more than 90 percent are sold as mixtures of both handed molecules because it's so hard to separate them," noted Dionne.
In a new study published Monday in Journal Nature Nanotechnology, a research team in Dionne's lab has shown one approach that holds promise for separating chiral molecules.
It involves a nanostructured filter that, when illuminated with a laser, attracts one handed specimen while repelling its mirror image.
Focused light can change the momentum of an object. This effect has been used to create tools known as optical tweezers, which allow scientists to manipulate particles with highly focused beams of light.
Although the idea of tweezing apart chiral forms has seemed appealing, many of the molecules are too small to be pulled apart by optical forces directly.
Yang Zhao, a postdoctoral fellow in the Dionne lab, overcame that weakness by creating a nanostructure that allows circularly polarized light to interact more strongly with small specimens.
The light path in the nanostructure maps a spiral in one direction but not the other. Once the chiral light has passed through this path, it interacts with molecules that complement its shape and pulls those downward.
The researchers built a tool called a chiral optical force microscope, which combines the optical tweezers with an atomic force microscope (AFM), a tool capable of resolving the chemical structure of a single molecule.
A chiral AFM tip served as the chiral specimen and, at the same time, mapped out the forces specific to the handedness of the tip.
They showed that the optical forces produced by their tweezers are strong enough to separate certain chiral molecules.
The team has not yet tested the tweezers on actual chiral molecules, according to a news release from Stanford, but Zhao has begun quantifying the forces they are able to apply to deoxyribonucleic acid (DNA) and certain proteins.
The next step will be assembling their tweezers into a sort of filter that can separate two forms of a drug or other molecules.
"We will put many of these nanostructures on a microfluidic chip where a drug of interest can be introduced," Zhao was quoted as saying in a news release. "If it works as we want it to, we should be able to have the drug separated upon illumination."
