diameter of deposited platinum clusters depended on the con-
centration of reducing agent (data not shown).
In conclusion, the enzymatic synthesis of a DNA block
copolymer composed of a poly(dG)ꢁpoly(dC) part and a poly-
[d(AT)] part from block copolymer-type template-primers was
achieved. We confirmed the sequence-selective platinum metal
deposition on the GC-part of the DNA block copolymers by gel
electrophoresis and AFM. DNA extension using modified
dNTPs, such as ligand-chelating metal ions, will contribute to
the fabrication of functional nanowires;26 for example, hetero-
nanowires composed of a metal and a semiconducting material.
This work was supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports,
Science, and Technology (MEXT), Japan. We thank the Post-
Silicon Alliance and Hokkaido Innovation through Nano
Technology Support (HINTS) supported by MEXT.
Notes and references
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Fig. 4 (a) AFM image of platinum metal bound to the DNA block
copolymer. A solution containing 1 mM dATP and 1 mM dTTP was
reacted for 6 h. After extension of the AT-part, the solution was
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difference is caused by formation of a G-quadruplex, AFM
measurement of nonmodified poly(dG)ꢁpoly(dC) indicated that
it formed a homogeneous linear structure and the height is
similar to that of the naked double-stranded DNA (Fig. S1,
ESIw).25 The increment of the height was observed after reduc-
tion of cisplatin bound to poly(dG)ꢁpoly(dC) and the height is
similar to that of platinum clusters on deposited on Lambda
DNA molecules.11 Therefore, the height increment after the
reduction of cisplatin bound to the DNA block copolymers
indicated the deposition of a platinum cluster on the DNA. The
length of segment A (500 nm) was within the range estimated
from electrophoretic results (Fig. 2). Some AFM images in-
dicate that the GC-part of the DNA block copolymers varied in
length (Fig. S2, ESIw). The stretches of DNA ending in tails
which appears significantly higher than the rest is caused by
folding of DNA ending in the process of the DNA transferring
onto a substrate.23 Accordingly, segment A could be identified
as the GC-part in the DNA block copolymer. This indicated the
successful enzymatic synthesis of the DNA block copolymer
and its sequence-selective modification of 1–2 nm platinum
clusters. Since cisplatin was mixed with the DNA block copo-
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stoichiometry was consistent with the deposition of 1–2 nm
platinum clusters (number of Pt atoms is about 50–300). The
ꢂc
This journal is The Royal Society of Chemistry 2008
4272 | Chem. Commun., 2008, 4270–4272