Published: March 29, 2011 r2011 American Chemical Society 4334 dx.doi.org/10.1021/la200743n | Langmuir 2011, 27, 4334–4338 LETTER pubs.acs.org/Langmuir Hybrid Macroscopic Fibers from the Synergistic Assembly Between Silica and Filamentous Viruses Eric Grelet,* Alexandra Moreno, and R  enal Backov Centre de Recherche Paul-Pascal, CNRS - Universit  e de Bordeaux, 115 Avenue Albert Schweitzer, 33600 Pessac, France ’ INTRODUCTION An abundance of composite biominerals exists in nature whose complexity gives rise to enhanced material properties. Oysters, corals, and diatoms are examples of living organisms who construct complex biominerals essential to their survival. 1À5 The control and function of biominerals evolved by these organisms naturally leads to the desire to engineer such archi- tectures by understanding and harnessing the power of biomi- neralization. A fundamental aspect is the study of biological mineralization that combines supramolecular assemblies with mineralization in order to address the key parameters occurring at the organicÀinorganic interfaces. This concerns for instance nucleation mechanisms, growth regimes, and polymorphism of inorganic matter. In such context, biological templates, such as viruses, ferritin, and self-assembled protein complexes, allow genetic programmability and site-specific chemistry, providing thereby a land of opportunities for the fabrication of novel materials with original functionalities. Genetically engineered and chemically modified viruses have been used extensively to direct material synthesis by controlling composition, mutation positions, and morphologies. 6À11 This work focuses on the elabora- tion of long, thin macroscopic hybrid fibers with large length to width aspect ratio by using one-dimensional (1D) self-organization of the filamentous fd virus. Such unidimensional microstructures exhibiting anisotropic properties have a high interest in different research areas, such as for instance electronics or optics. 12 ’ RESULTS AND DISCUSSION The fd bacteriovirus is a charged monodisperse rodlike particle with a high aspect ratio (contour length of 880 nm and diameter of 6.6 nm). This biological polyelectrolyte is semiflexible (persistence length of 2.8 μm) and has a molecular weight of M W = 1.64 Â 10 7 g/mol. 13 Fd is formed by a single stranded DNA, around which about 2700 identical coat proteins are helicoidally wrapped following a 5-fold rotation axis combined with a 2-fold screw axis. 14,15 A representation of the fd virus surface is given in Scheme 1. Due to the rodlike shape of the bacteriovirus, aqueous fd suspensions have been shown to depict different self-organized states: isotropic liquid, chiral nematic, 16 smectic, 17 columnar, and crystalline phases, 18 by increasing the fd virus concentration. Each coat protein is formed by 50 amino acids, which results in a net charge (carried by ionic amino acids) of about À3e per protein in water at neutral pH, corresponding to a linear charge density of about 10e/nm on the virus. 19 The fd virus isoelectric point is at pH = 4.2, above which the virus surface is negative while being positive below. 19 This has to be compared with the silica isoelectric point being at pH 2.1. 20 Therefore, a small pH window exists, between pH = 2.1 and pH = 4.2, where positive silica clusters attract negatively charged viruses electrostatically. Scheme 1. Electron Microscopy Image of the fd Virus (top) Which Exhibits a Length of 880 nm and a Diameter of 6.6 nm and Schematic All-Atom Representation of Its Surface (bottom) 14,16 a a Proteins with a given color are related by a 5-fold symmetry axis. The distance of 3.3 nm corresponds to the protein periodicity along the capsid. Received: February 25, 2011 Revised: March 23, 2011 ABSTRACT: In this work, we report the elaboration of macroscopic hybrid virusÀsilica fibers. By using a silicate sol as inorganic precursor combined with the filamentous fd virus, well-dispersed hybrid fibers are obtained in solution. These macroscopic fdÀsilica fibers exhibit a narrow distribution of their diameter, while their length is at the millimeter scale. A scenario of the morphosynthesis is proposed to account for the formation of these high aspect ratio hybrid fibers.