Review paper Fabrication of Pd–DNA and Pd–CNT hybrid nanostructures for hydrogen sensors Satoshi Ohara a,⇑ , Yoshiharu Hatakeyama b , Mitsuo Umetsu c , Zhenquan Tan a , Tadafumi Adschiri b,d a Joining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan b Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan c Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, 6-6-11 Aoba, Aramaki, Aoba-ku, Sendai 980-8579, Japan d Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Miyagi 980-8577, Japan article info Article history: Received 8 March 2011 Received in revised form 27 April 2011 Accepted 13 May 2011 Available online 26 May 2011 Keywords: Palladium DNA CNT Hybrid nanostructures Hydrogen sensors abstract This review reports fabrication methods for ordered metallic nanostructures such as nanowires and nanoparticles based on deoxyribonucleic acid (DNA) templates. The phosphate groups in DNA are nega- tively charged; consequently, the DNA conformation may mineralize metals, e.g., palladium (Pd) at a rel- atively high metal concentration. We successfully form unique spherically shaped moss-like hybrid Pd nanoparticles using the small compacted globular state of DNA by controlling the reductive reaction. Pd can absorb hydrogen to become PdH x , and hydrogen storage increases the electrical resistance and volume of Pd materials. Hence, the use of this material is attracting growing interest as a reliable, cheap, ultracompact, and safe hydrogen sensor. Pd–DNA hybrid nanoparticles can be used as highly sensitive hydrogen sensors, which exhibit a switch response that depends on the volume expansion in a cyclic atmosphere exchange. This paper also shows the fabrications of Pd–carbon nanotube (CNT) hybrid nanostructures. Ó 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. Contents 1. Introduction ......................................................................................................... 559 2. Pd–DNA hybrid nanostructures .......................................................................................... 560 3. Hydrogen-sensing properties............................................................................................ 561 4. Pd–CNT hybrid nanostructures .......................................................................................... 563 5. Conclusions .......................................................................................................... 564 Acknowledgments .................................................................................................... 564 References .......................................................................................................... 564 1. Introduction The 20th century was the so-called age of new material synthe- sis [1]. Syntheses of new substances were essential to attain new material properties. However, recent material R&D has focused on controlling material functions via the material structure. One example is nanotechnology. To control the material structure, the process is more important than the synthesis. For example, the size and shape of nanoparticles significantly de- pend on the operating conditions during the crystallization process. Some semiconductor materials show a strong photo-luminescence, and the particle size can control the wavelength (quantum size effect). Consequently, changing the nanoparticle size of quantum dots (QDs) results in a wide range of color using the same excitation wavelength for CdSe, CdTe, CdS, etc. [2]. The next stage of the nano- technology will be to assemble nanomaterials because this is a foreseeable future target in various industries. In device production by assembling structured materials, fabrication is a key technology. Thus, science and technology for materials is shifting from synthesis towards processing and fabrication. Nanobiotechnology has great potential in the fabrication of nanostructured materials where specific interactions between molecules of deoxyribonucleic acid (DNA) or peptide are used to create assemblies of multi-component nanomaterials or nano- blocks, such as QDs, nanocrystals, biomaterials, and bio-reactive nanomaterials. Controlling the assembly of various bio-molecules and nanoblocks will be crucial in the fabrication of multi-component 0921-8831/$ - see front matter Ó 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved. doi:10.1016/j.apt.2011.05.006 ⇑ Corresponding author. E-mail address: ohara@jwri.osaka-u.ac.jp (S. Ohara). Advanced Powder Technology 22 (2011) 559–565 Contents lists available at ScienceDirect Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt