Technology Research News
Although human-machine hybrids are likely
to remain in the realm of science fiction for decades, researchers are
beginning to meld tissue and technology at the cellular level.
Bridging the wide communications gap between biology and electronics by
connecting a cell to a semiconductor
means both the cell and the electronic device can potentially take
advantage of the best attributes of the other.
Researchers at the University of Texas at Austin have taken a step toward
cell-semiconductor communications by soldering semiconductors to nerve
cells. Key to the process is the solder -- a modified peptide molecule
that binds to a human neuron protein on one side, while the other sticks
to a microscopic particle of semiconductor material, or nanocrystal.
"We make particles in a solution," and stick the modified peptides onto
the surface of the particles, said Brian Korgel, an assistant professor
of chemical engineering at the University of Texas at Austin. "The particles
[then] stick to the cells in specific locations."
The specialized peptide molecule connects a particle to a biological receptor
that sticks out of the nerve cell membrane. The connection brings the
particle to within 20 nanometers of the electrically-active cell membrane,
which is closer than previous methods. Nerve cells can be grown on semiconductor
materials, but do not stick as closely to the electronics; previous research
efforts have grown nerves on electronics, but leave a 50-nanometer gap.
As cells go, nerve cells are relatively large -- the cells the researchers
used were 60 microns in diameter, which is a little over 10 times the
size of a red blood cell, and nearly the diameter of human hair. At 5
nanometers, the particles were more than 5,000 times smaller. A micron
is one thousandth of a millimeter; a nanometer is one thousandth of a
Although it may be difficult to get them together, nerve cells and electrical
components do have something in common -- they both communicate using
Nerve cells use changes in their electrical fields to create specific
nerve firing patterns. "This is one of the underlying properties that
enable brain functions like memory," said Korgel. Electrical field-effect
transistors turn on and off based on the amount of electricity flowing
through a gate electrode.
This mutual responsiveness to electrical fields makes intermaterial communications
possible, said Korgel. "The nerve cell can effectively function as a gate
on a field-effect transistor if the two materials are interfaced properly,"
Nerve-semiconductor links could eventually be used to allow nerves to
directly control prosthetics, said Christine Schmidt, an assistant professor
of biomedical engineering at the University of Texas at Austin.
“Bioprosthetic devices [like] retinal implants [and] mechanical prosthetics
could be connected to the nervous system and brain using semiconductor
materials such as those we are investigating.” In addition, existing devices
like cochlear implants may be improved using these materials, she said.
Cells and nanocrystals could also be combined to detect tiny quantities
of chemicals that are toxic to cells, said Korgel. There's also potential
for using nerve cells to boost computer memory devices, he said. "One
idea that I find particularly exciting is the prospect of combining nanocrystals,
nerves and conventional microelectronics to create nerve-cell memory devices,"
It is also theoretically possible to use optically-activated nanocrystals
to probe cells to study their internal electro-chemical reactions, according
The researchers are currently looking into mechanisms that will allow
the semiconductor nanocrystals to communicate with the nerve cells, said
Korgel. "If we stimulate the nanocrystal with light... will the nerve
feel the stimulus? Normally a nerve cell would not be affected by light,
but with the nanocrystals attached, could we [change] the function of
the nerve cells? These are the questions that we are currently trying
to answer," he said.
The idea and methods are excellent, said Shuguang Zhang, associate director
of the Center for Biomedical Engineering at the Massachusetts Institute
of Technology. "Such direct linkage will likely find application in understanding
the nerve connections and the strength of the connections through the
fine adjustment of the electric input. This is a significant step forward
to interface nerve cells with conducting and semiconducting materials,"
The method may eventually be useful in repairing damaged nerve systems;
it could also serve to "interface the 40-year young semiconducting industry
with biology that has evolved over billions of years. It is one step closer
to... Star Trek," Zhang said. However, because dry computers and water-based
cells are so inherently different "there still remains a big gap and challenge
to be worked out," he said.
The researchers have extended the use of luminescent nanocrystals in biological
applications, but it remains to be seen how useful the interface will
be because the nanocrystals may still not be close enough to the membrane
of the cell to interface with it electrically, said Peter Fromherz, a
professor of biophysics at the Max Planck Institute of Biochemistry. "These
particles are so far from the membrane that they feel little of the electrical
field across the membrane," he said.
There are many hurdles to overcome before cells and semiconductor nanocrystals
will combine in practical products, said Korgel. "This is really an unexplored
area and we have much to learn," he said. Practical uses are probably
a decade away, "but this is only a guess," he said.
Korgel and Schmidt’s research colleagues were Jessica O. Winter and Timothy
Y. Liu. They published the research in the October 30, 2001 issue of Advanced
Materials. The research was funded by the National Science Foundation
(NSF), the Welsh Foundation, DuPont, the Petroleum Research Fund, the
Gilson Longenbaugh Foundation and the Whittaker Foundation.
Timeline: 10 years
Funding: Government, Corporate, Private
TRN Categories: Biological, Chemical, DNA and Molecular
Computing; Materials Science and Engineering; Semiconductors
Story Type: News
Related Elements: Technical paper, "Recognition Molecule
Directed Interfacing between Semiconductor Quantum Dots and Nerve Cells,"
Advanced Materials, October 30, 2001.
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