DNA-Templated Silver Nanorings** By Anatoly A. Zinchenko,* Kenichi Yoshikawa, and Damien Baigl Nanostructures of noble metals with well-defined shapes and sizes are increasingly attracting the attention of scientists in the fields of catalysis, electronics, photonics, information storage, optoelectronics, biological labeling, etc. The further development and practical applications of nanostructures are expected to increase rapidly because of their interesting opti- cal, electronic, and magnetic properties. [1] In this context, im- portant knowledge of the direct preparation of metallic nano- structures of controlled size and shape has been developed over the past few years, and various morphologies, such as spherical nanoparticles, [2] nanocubes, [3] nanoprisms, [4] nano- plates, [5] or nanobelts, [5] can now be prepared in a controlled way. However, since these techniques are based on the direct- ed growth of particles in the reaction medium, they can only lead to shapes of a simple topology, such as spheroids, ellipsoids, or polyhedrons. In contrast, nanoparticles with a toroidal shape (nanoring) can not be produced by a direct growth technique. Hence, the only way to produce such a morphology is to use a toroidal template of nanometer-scale dimensions. Elaborate and successful methods to prepare sil- ver or gold rings based on the use of a nanoparticle array or a mesoporous membrane as a primary template, were recently described by Xia and co-workers [6] and Yan and Goedel, [7,8] respectively. However, these techniques provide rings with a minimal size of 0.5 lm that can not be directly dispersed in an aqueous medium. On the other hand, due to the specific inter- action between DNA and silver ions, DNA is an ideal tem- plate to build silver nanostructures. This principle has been used successfully to produce nanoparticle arrays on a DNA scaffold, [9,10] or DNA-templated silver nanowires. [11,12] How- ever, the ability of DNA chains to form toroidal conden- sates [13] as a result of the DNA-folding transition (DNA con- densation [14] ) has not been hitherto noticed by materials scientists. The ability of DNA to condense into well-defined toroids provides a unique opportunity to use them as tem- plates to create silver toroidal nanostructures (nanorings) of controlled shape and dimensions. In this communication, we describe a one-pot, three-step, simple preparation of well-de- fined silver nanorings (100 nm in diameter) dispersed in water, based on the use of dilute solutions of DNA conden- sates as nanostructured templates. DNA is a semiflexible, highly charged polyelectrolyte that assumes an elongated-coil conformation in water due to the electrostatic repulsion between the negatively charged mono- mers. DNA molecules usually fold into tightly packed toroidal condensates with an outer diameter of typically 70–90 nm [13,14] in the presence of hydrophilic neutral polymers, [15] or upon the addition of a small amount of condensing agent, such as cat- ionic polyamines, [13] multivalent metal cations, [16] and cationic surfactants, [17] to a dilute DNA solution. The role of the con- densing agents is to induce an attraction between the DNA monomers (chain neutralization or crowding effect), and the toroidal morphology is adopted because of the native rigidity of the DNA double-stranded chain. [18,19] Advanced Materials 0000, 00, 0–0 1 DOI: 10.1002/adma.200501549 © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim – [*] Dr. A. A. Zinchenko, Prof. K. Yoshikawa,Dr. D. Baigl Department of Physics Graduate School of Science, Kyoto University Kyoto 606-8502 (Japan) E-mail: zinchenko@chem.scphys.kyoto-u.ac.jp Dr. D. Baigl École Normale Supérieure, Département de Chimie UMR CNRS 8640 24, rue Lhomond, F-75231 Paris, Cedex 05 (France) [**] The authors thank Prof. K. Endo (Kanazawa University, Japan) for fruitful discussions and Prof. T. Kanbe (Nagoya University, Japan) for help with electron microscopy observations and discussions. This work was supported in part by fellowship No. P04154 from the Japan International Science and Technology Exchange Center (JISTEC), fellowship No. P03200 from the Japanese Society for the Promotion of Science (JSPS), and a Grant-in-Aid for the 21st Cen- tury COE ‘Center for Diversity and Universality in Physics’ from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.