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JAPAN NANONET BULLETIN
-- 45th Issue -- May 26, 2005
Nanotechnology Researchers Network Center of Japan
Ministry of Education, Culture, Sports, Science and Technology (MEXT)
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IN THIS ISSUE
Nanonet Interview:
"Returning to physical instrumentation
-- Decoding DNA sequences by phase contrast electron microscopy --"
Kuniaki NAGAYAMA, Professor, Okazaki Center for Integrative
Bioscience and National Institute for Physiological Sciences, National
Institutes of Natural Sciences
Young Researchers' Introduction:
"Fabrication of DNA-metal hybridized nano wires by selective
electroless plating"
Kuniharu IJIRO, Professor, Research Institute for Electronic Science
(RIES), Hokkaido University
-- NANO CALENDAR --
For information on nanotechnology related symposiums and conferences
held in the world,
http://www.nanonet.go.jp/english/calendar/
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NANONET INTERVIEW
Returning to physical instrumentation
-- Decoding DNA sequences by phase contrast electron microscopy --
(Issued in Japanese: December 9, 2003)
Kuniaki NAGAYAMA, Professor, Okazaki Center for Integrative
Bioscience and National Institute for Physiological Sciences,
National Institutes of Natural Sciences
Determining the structure of proteins using multidimensional NMR,
developing technology for protein molecular array and colloidal
particle array based on self-assembly and decoding DNA using electron
microscopes are the research areas in which Prof. Nagayama has been
involved. "It may sound as if there were no similarities among these
fields, but the basis for my research is physical instrumentation,"
says Prof. Nagayama, who developed a complex observation scheme that
is one of the most powerful methodology in physical instrumentation.
"Optical image analysis using complex functions is a miracle because
any information obtainable from optical objects can be completely
retrieved. We can usually see only amplitude images which are a part
of the information obtainable from optical objects," says Prof.
Nagayama. The information that usually cannot be seen involves wave
phase. In 1999, he proposed a complex observation scheme in order to
obtain wave phase information, and two years later, he proved his
concept by developing a phase contrast electron microscope.
A phase contrast electron microscope has various observation methods
due to the phase plates set at the back focal plane (BFP). Prof.
Nagayama developed two phase contrast methods. One is a Zernike phase-
contrast method and the other is a differential interference contrast
method called Hilbert differential contrast method. He says, "Although
living organisms are generally transparent to an electron wave, the
electron wave always changes its phase when scattered by an object.
Living organisms can be observed if phase contrast is obtained through
the scattering wave whose phase is manipulated by a phase plate." The
highest-contrast images ever were produced by applying a quarter wave
phase shift to all of the scattering waves in the Zernike phase-
contrast method and applying a half wave phase shift exclusively to
scattering waves transferring through a partial frequency space such
as a positive frequency space. An object's optical information can be
reconstructed by combining phase images and an amplitude image that
was obtained by a conventional method using only an aperture, and it
is this complex observation scheme that Prof. Nagayama developed.
What Prof. Nagayama has been trying to observe using phase contrast
electron microscopes is membrane proteins, which are hard to
crystallize. He says, "We can observe a single protein, and so, we
have taken on the challenge to do experiments with single proteins."
In 2003, he was able to analyze the structure of a human ion channel
using an phase contrast electron microscope with 30 A (angstrom)
resolution. His goal was to establish bioelectronics using two-
dimensional crystals of protein molecules when he began research on
self-assembly in proteins. He says, "I would like to relate electric
signals to chemical reactions, for which the most suitable object is a
kind of membrane proteins, channel." The development of phase contrast
electron microscopes encouraged him to try to achieve his goal again.
Another goal has been to produce a "terabase sequencer" which can
determine the sequence of a single molecular DNA using a phase
contrast electron microscope. With a terabase sequencer, four kinds of
bases, which are complimentarily bound to DNA, are synthesized to each
of which a specific metal cluster is attached as a label. The labeled
bases are then bound to single-strand DNA and analyzed with an
electron microscope. If the terabase sequencer is built, a sequence of
one billion base pairs can be decoded in just one day. It will perform
the analysis 1,000 times faster than any conventional system, and thus,
the cost of decoding human DNA would be only about 3,000,000 yen,
which is a thousandth of what currently costs.
When Prof. Nagayama was a graduate student, a DNA decoding method
using an electron microscope was studied in a biophysics lab of which
he was a member. However, chemical decomposition methods, such as the
Sanger method and the Maxam-Gilbert method, were developed before his
group could develop its own method. He says, "I was shocked because I
was going to start a new field in biology with physical
instrumentation. In biology, physics may always fall behind chemistry.
I felt defeated." His interest shifted to other fields of research.
However, because the resolution of current electron microscopes is
under 1 A (angstrom) in materials science, it should be possible to
decode DNA using an electron microscope. He felt encouraged to try
decoding DNA again. He says, "I have to win in this field otherwise I
cannot die. So that's why I came back to this field."
(Interviewer: Kuniko Ishiguro, Cosmopia Inc.)
For more information,
http://www.nanonet.go.jp/english/mailmag/2005/045a.html
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YOUNG RESEARCHERS' INTRODUCTION
Fabrication of DNA-metal hybridized nano wires by selective
electroless plating
(Issued in Japanese: January 13, 2004)
Kuniharu IJIRO, Professor, Research Institute for Electronic Science
(RIES), Hokkaido University
Recently double-stranded DNA molecules have attracted attention as new
functional materials, such as a building block for suprastructures. We
have studied novel nano fabrication methods by using single DNA
molecules immobilized on a substrate as a template. It is known that a
DNA molecule, which is a kind of anionic polyelectrolyte, can be bound
to a cationic lipid monolayer to form a polyionic complex through
electrostatic interactions. When the cationic lipid was spread onto an
aqueous DNA solution, the polyion complex monolayer consisting of the
cationic lipid and DNA was formed, and DNA can be transferred to a
solid substrate using a vertical lifting method. We have found that
transferring with a slow lifting speed gives stretched single DNA
molecules immobilized on a glass substrate. We have investigated the
fabrication of metal nanowires by electroless plating of stretched
single DNA molecules immobilized on substrates as a template. AFM and
SEM measurements after the metallization procedure showed that thin
lines (ca. 20 nm height and ca. 50 nm width) were fabricated on the
substrate. Fine silver particles were deposited along the stretched
DNA molecules selectively. We are attempting to measure electronic
conductivity of the metal nano wire using conducting AFM.
For more information,
http://www.nanonet.go.jp/english/mailmag/2005/045b.html
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