Atomic scopes eye living tissue
Technology Research News
a lot to a butterfly's wing. Its barely visible scales are made from fragile,
infinitesimal structures that underlie the insect's ability to perform a
wide variety of precise maneuvers.
Researchers from Oak Ridge National Laboratory and North Carolina
State University have used a scanning probe microscope to look at the structure
of a butterfly's wing at a resolution of five nanometers, or two and a half
times the width of DNA molecule. A nanometer is one millionth of a millimeter,
or the span of 10 hydrogen atoms.
The pictures show individual chitin fibrils, making it possible
to study the mechanical properties of the wing on the level of a single
structural element. The pictures are a proof-of-concept that show that it
is possible to use scanning probe microscopes to analyze material from living
Scanning probe microscopy is usually used to examine inorganic materials
like the ferroelectrics used in electronics, and organic materials like
plastics. Scientists have also been able to use the instruments to study
isolated biological molecules like DNA.
The ability to see living tissue at the molecular level will help
scientists understand the properties of all kinds of biosystems, said Sergei
Kalinin, a research and development staff member at the Oak Ridge National
Laboratory. A better understanding of how living structures function could
enable better artificial materials, assessments of disease, and drug and
physical therapies, he said.
Scanning probe microscopes show information about the surface structure
and electrical, magnetic, optical and mechanical properties of a material.
The microscopes allow researchers to image tiny areas using friction, electricity,
magnetism and acoustics.
Scanning probe microscopes consist of a microscopic tip attached
to a tiny arm. The basic operation mode is to drag the tip across a sample
and measure how much the arm is deflected, which reveals the sample's height
at each point. Scanning in a series of lines creates a topographic image
of the sample.
Material properties are measured using other modes, including current,
which measures a sample's electrical conductivity; electrostatic, which
measures the electrostatic interaction between the tip and the sample; magnetic,
which measures the local magnetic field at each point on a sample; acoustic,
which uses changes in vibration rates to measure elasticity; pulsed, which
measures stickiness; and scanning coupling, which uses the quantum ability
of electrons to jump across a gap to measure electrically conducting samples
in atomic detail.
"We attempted to use several scanning probe microscope modes developed
to study mechanical and electromechanical properties in... semiconductors,"
said Kalinin. "To our surprise, we found that using acoustic imaging allows
imaging much finer details of the internal structure of... biological systems
than we believed possible," he said.
The basic topographic image of the butterfly wing shows details
down to about 100 nanometers, including the mesh structure that enables
high mechanical stability and rigidity of the wing, said Kalinin. The acoustic
imaging mode shows details down to five nanometers. This allows for the
study of mechanical properties "on the level of single structural element
forming the biological tissues -- chitin rods," he said.
The ultimate goal is to establish methods of using the microscope
to qualitatively measure properties of biological tissue that are too small
or too fragile to be studied by conventional testing, said Kalinin. "To
be able to see and quantitatively measure, rather than guess, mechanical
and electromechanical properties on the nanoscale can well hold the key
for unraveling the origins of biological functionality in these materials,"
The researchers also want to push the technology to its limits.
"We want to achieve maximally high resolution," said Kalinin. "Can we probe
a single molecule inside [a] biological system?"
Possibilities include understanding the effects of hard tissue diseases
like dental cavities and osteoporosis, and understanding tissue behaviors
that could provide the basis for drug and physical therapies and methods
of identifying cancer cells, said Kalinin. "We're interested in making our
measurements quantitative, so we can say not only whether a particular region
is softer or harder, but exactly how hard or soft it is," he said.
This is a very complex task that requires mathematical tools to
describe tip-surface contact mechanics and a way to measure the shape of
the tip, said Kalinin.
The researchers are exploring using scanning probe microscopes to
study electrical and electromechanical interactions in biological tissues,
which could provide insights into bone growth, muscular activities and other
phenomena, said Kalinin. They are also working with other scientists to
use scanning probe microscopy to study cell development and differentiation,
It will be possible to take practical measurements of hard tissues
like bones and teeth within several years, said Kalinin. Establishing guidelines
for quantitative measurements and developing the appropriate calibration
standards for those measurements will take longer, he said.
Kalinin's research colleague was Alexei Gruverman, an associate
research professor of materials science at North Carolina State University.
The research was funded by the Oak Ridge National Laboratory and the National
Timeline: 1-5 years
TRN Categories: Applied Technology
Story Type: News
Related Elements: None
February 9/16, 2005
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