Biological Templated Synthesis of Water-Soluble Conductive Polymeric Nanowires Zhongwei Niu, † Jie Liu, ‡ L. Andrew Lee, † Michael A. Bruckman, † Donggao Zhao, § Goutam Koley,* ,‡ and Qian Wang* ,† Department of Chemistry and Biochemistry and Nanocenter, UniVersity of South Carolina, 631 Sumter Street, Columbia, South Carolina 29208, Department of Electrical Engineering, UniVersity of South Carolina, 301 South Main Street, Columbia, South Carolina 29208, and The Electron Microscopy Centre, UniVersity of South Carolina, 715 Main Street, Columbia, South Carolina 29208 Received August 23, 2007; Revised Manuscript Received October 21, 2007 ABSTRACT One-dimensional (1D) conductive nanowire is one of the most important components for the development of nanosized electronic devices, sensors, and energy storage units. Great progresses have been made to prepare the 1D-conducting polymeric nanofibers by the low concentration process or the synthesis with hard or soft templates. However, it still remains as a great challenge to prepare polymeric nanofibers with narrow dispersity, high aspect ratio, and good processibility. With the rod-like tobacco mosaic virus as the template, 1D-conducting polyaniline and polypyrrole nanowires can be readily prepared via a hierarchical assembly process. This synthesis discloses a unique way to produce composite fibrillar materials with controlled morphology and great processibility, which can promote many potential applications including electronics, optics, sensing, and biomedical engineering. Self-assembled proteins, such as plant viruses and other bionanoparticles, exhibit fascinating structural features and sophisticated chemistries, which are advantageous charac- teristics for the development of novel nanoscale materials. 1-8 For instance, the native tobacco mosaic virus (TMV) particle possesses a unique tubelike structure and distinctive physio- chemical properties that have made this system a robust and attractive platform for the deposition of inorganic materials on either the interior or the exterior surface to form one- dimensional (1D) nanostructures. 9-13 The virus is assembled from 2130 identical coat proteins arranged helically around a single strand of RNA. The entire particle measures 300 nm in length and 18 nm in diameter, and can be isolated from infected tobacco plants in gram quantities with relative ease. The virion remains intact at temperatures up to 60 °C and at pH values between 2 and 10. 14 Moreover, recent studies have shown that the surface properties of TMV can be chemically or genetically manipulated without interfering the integrity and morphology of virus. 1,15,16 Evidently, TMV- based materials have already shown great potential in nanoelectronics. 8,17 On the other hand, polyaniline (PANi) and other conduc- tive polymers has been extensively studied for optical and electronic applications. 18-20 Many practical syntheses of 1D nanostructured PANi have been developed. 21-26 However, preparation of conductive PANi nanowires with controllable morphologies and sizes, especially with good processibility, is still a challenge. In this letter, we demonstrate the fabrication of water-dispersible, conductive PANi nanowires using TMV as a template. Furthermore, much longer conductive PANi/TMV nanowires (>300 nm, greater than the length of a native TMV particle) can also be formed by a hierarchical assembly process. 27-29 As shown in Scheme 1, conductive polyaniline/TMV composite nanowires can be readily prepared by incubation of TMV, aniline, poly(sulfonated styrene) (PSS), and am- monium persulfate (APS) at room temperature. Highly negative-charged PSS is used here both as the dopant acid to enhance the conductivity of PANi and to improve the stability of composite fibers in aqueous solution. As shown in Figure 1, a green transparent solution of PANi/TMV composites were observed after a 24 h reaction at pH 4, indicating the formation of the emeraldine form of PANi. The color of the reaction mixture changed to yellow at pH 5.0. We attribute the color change to the formation of branched poly or oligo-anilines at higher reaction pH. * Corresponding authors. E-mail: (Q.W.) wang@mail.chem.sc.edu; (G.K.) koley@engr.sc.edu. † Department of Chemistry and Biochemistry and Nanocenter. ‡ Department of Electrical Engineering. § The Electron Microscopy Centre. NANO LETTERS 2007 Vol. 7, No. 12 3729-3733 10.1021/nl072134h CCC: $37.00 © 2007 American Chemical Society Published on Web 11/17/2007