Nano-olives are made up of an iron oxide “olive” with an iron and platinum “pimento.” Together the components make a highly magnetic particle structure, which may one day be useful for data storage in computers. Image: The Schaak/Williams research groups, Penn State. |
A
team of Penn State University
scientists has invented a new system that uses magnetism to purify hybrid
nanoparticles—structures that are composed of two or more kinds of materials in
an extremely small particle that is visible only with an electron microscope. Team
leaders Mary Beth Williams, an associate professor of chemistry, and Raymond
Schaak, a professor of chemistry, explained that the never-before-tried method
will not only help scientists to remove impurities from such particles, it also
will help researchers to distinguish between hybrid nanoparticles that appear
to be identical when viewed under an electron microscope, but that have
different magnetism—a great challenge in recent nanoparticle research. The
system holds the promise of helping to improve drug-delivery systems,
drug-targeting technologies, medical-imaging technologies, and electronic
information-storage devices. The paper will be published in Agewandte Chemie.
Schaak
explains that purifying hybrid nanoparticles presents an enormous challenge,
especially when nanoparticles are designed for human use—for example, for drug
delivery or as a contrast-dye alternative for patients undergoing MRI studies.
“The problem is that although molecules are synthesized and purified using
well-known methods, there have not been analogous methods for purifying
nanoparticles,” Schaak says. “Hybrid particles are especially
challenging because the methods that are used to make them often leave
impurities that are not easily detected or removed. Impurities can change the
properties of a sample, for example, by making them toxic, so it is a major
challenge to find ways to remove such impurities.”
The
team combined forces to figure out a way to purify hybrid nanoparticles.
“We had to find a way to separate impurities from the target
nanoparticles, even when these particles are similar in size and shape, because
of the potentially very big consequences of impurities on the ultimate use of
nanoparticles,” Schaak says. The team’s new system does just that. The
innovative technique uses the magnetic components of nanoparticles to tell them
apart and to separate impurities from the target nanoparticle structures.
“Our
method uses magnetic fields to slow the flow of particles through tiny glass
tubes called capillaries,” Williams explains. “We use a magnet to
pull magnetic particles against the wall of the tube and, when the magnetic
field is reduced, the particles flow out of the capillary. Magnetism increases
as particle volume increases, so small and gradual changes in the magnetic
field let us slowly separate and distinguish between nanoparticles based on
even minute magnetic and structural differences.”
The
team’s paper shows how magnetic fields can be used to separate and distinguish
between hybrid nanoparticles in a mixture of slightly different structures and
shapes. In one example, the researchers separated “nano-flowers,” so
named because of their petal-like arrangement around a solid core, from
spherically shaped particles. Williams explains that the magnetism of the
particles depends on their shape, so particles of a different shape adhere to
the capillary wall when different magnetic fields are applied, thus allowing
the researchers to distinguish between the different particles.
In
another example in the paper, the researchers showed how the magnetic-field
method can be used with a class of nanoparticle dubbed the
“nano-olive,” which is a spherical particle comprised of two
different materials joined in a shape reminiscent of an olive. The nano-olives,
which are composed of iron, platinum, and oxygen, may look alike, but they may
have slightly different internal compositions that are impossible to detect
under a microscope. “For example, some may have more iron content,”
Schaak explains. “This is a property we can use for purification with our
method because these nanoparticles are a bit more magnetic. They stick along
the walls of the capillary tubes more easily, while more magnetically weak
particles flow out.”
The
new purification and separation method has many applications, especially within
the fields of medicine and diagnostics. For example, nanoparticles could be
used in lieu of contrast dye when patients undergo MRI imaging studies. Such
particles could be used to track where a drug is traveling in the human body.
“Some patients are allergic to traditional contrast dyes, so nanoparticles
offer a promising alternative,” Williams says.
Williams
also explains that one of the very futuristic dreams of nanoparticle research
is that it one day may be used to improve cancer-fighting drugs.
“Unfortunately, chemotherapy drugs don’t discriminate: They attack healthy
tissue, as well as cancerous tissue,” Williams says. “If we could use
nanoparticle technology to manipulate exactly where the drugs are going, which
tissue they attack, and which they leave alone, we could greatly reduce some of
the bad side effects of chemotherapy, such as hair loss and nausea. But to do
this we need to be able to separate out nanoparticle impurities to make them
safe for medical use. That’s where this new technology comes in.”
