Genetically Induced In Situ‐Poling for Piezo‐Active Biohybrid Nanowires

Abstract

ii) nonferroelectric materials. In both classes, a high macroscopic piezoelectric response, which is the average over all crystallites, is connected with the polar axes of the crystallites parallel aligned and with the same force direction. [6] In ferroelectric materials the direction of the polar axes can be permanently aligned postsynthesis by a strong electric field, which is referred as poling. [6a] However, the nonferroelectric piezo-active materials, like zinc oxide (ZnO), gallium nitride (GaN), beryllium oxide (BeO), or cadmium sulfide (CdS), do not allow the reorientation of the polar axes. In such materials, the maximum piezoelectric response of a crystallite is linked to one of its crystallographic axis (Figure 1a), which cannot be aligned postsynthesis. [5,7] In piezo-active materials the polarization is connected to the ordered alignment of electrical dipoles. [8] In order to synthesize piezo-active nonferroelectric materials either the direction of crystal growth has to be controlled [9] or the crystallite dipoles have to be aligned in a freely moveable state, e.g., in solution.To influence the deposition of inorganic materials, template structures inducing a force field were reported. Various template classes, e.g., polyelectrolytes, [10] peptides, [11] or biological entities, like viruses [12] and phages, [13] have been applied to control the morphology [14] of the inorganic phase or the mechanical performance of the hybrid material. [15] For such bioinspired synthesis approaches, M13 phage templates are of specific interest. M13 phages are nonpathogenic for humans and provide a nanowire-like structure (6 × 900 nm 2 ), which is precisely replicated in bacteria. The phage particles are robust and resistant to heat (>80 °C), mechanical stresses, and various solvents. [16] The protein coat, encapsulating the DNA genome, consists of five different proteins (p3, p5, p7, p8, and p9), which can be modified. The major coat protein p8 has dipole character with a positively charged C-terminus, interacting with the phage DNA and a negatively charged N-terminus facing the environment. [17] Due to the noncentrosymmetric arrangement of the p8 proteins, which are helically arranged around the central DNA strand, the M13 phage template represents a net dipole. [18] Moreover, the dipole strength can be further enhanced by the genetic modification of the major coat protein, which was shown in Polycrystalline piezo-active materials only exhibit a high macroscopic piezoresponse if they consist of particles with oriented crystal directions and aligned intrinsic dipole moments. For ferroelectric materials, the postsynthesis alignment of the dipoles is generally achieved by electric poling procedures. However, there are numerous technically interesting non-ferroelectric piezo-active materials like zinc oxide (ZnO). These materials demand the alignment of their intrinsic dipoles during the fabrication process. Therefore, in situ-poling techniques have to be developed. This study utilizes genetically modified M13 phage ...

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