German scientists have used peptides and pH to control the organisation of functionalised nanoparticles. 

Coiled coil peptides consist of several -helical peptides wound together like a rope to form a left-handed coil. Beate Koksch, at the Free University of Berlin, and colleagues have found that a coiled coil peptide can be used to direct the assembly of gold nanoparticles. Koksch also showed that peptide's directing ability can be switched on and off by varying the pH. Professor Koksch explains more about her work in the short interview below.

1. Please explain, for a non-specialist, the significance of your article. 

The interparticle distance and the regularity of the assembly are two key features that determine the magnetic, optical and electronic properties of nanoparticles. For that reason, the organization of nanoparticles into defined networks with the help of biomolecules that exhibit highly selective and specific binding properties as well as unique functionalities is of great current interest to materials science and a variety of medicinal applications. The -helical coiled coil folding motif combines the manifold functionalities of peptides with the structural stability and self-replication properties of nucleic acids. We were able to demonstrate the superiority of the -helical coiled coil folding motif not only as a defined structural template but also as a self-organizing system for the organization of gold nanoparticles. Therefore, our results offer a new route to control by pH the assembly and optical properties of nanoparticle-peptide hybrid systems in a switchable manner. 

2. What has motivated you to conduct this work? 

Metal and semiconductor nanoparticles represent highly functional building blocks for the construction of materials that have technological applications. Importantly, many properties of these materials are not only related to their composition, size, or shape but also to the spatial arrangement of nanoparticles within the material. For that reason, we were particularly interested in using the symmetry of the -helical coiled coil folding motif for this kind of arrangement. Furthermore, we wanted to use electrostatic interactions between peptides and nanoparticles for the organization of nanoparticles since electrostatic forces are a promising approach to direct this assembly by pH changes in a switchable manner. 

3. Where do you see this work developing in the future? 

We continue to study the variation of the size ratio between both components as well as the oligomeric state of the coiled coil peptide in order to control the symmetries of nanoparticle arrangement. 

4. Are there any particular challenges facing future research in this area? 

In the coming decades, nanomaterials are considered likely to revolutionize many areas, including information technology and biomedical industries. With regard to the construction of bionanomaterials that have technological applications, great progress has been achieved in the last few years. Nonetheless, the directed assembly of nanoparticles into well-defined superstructures with tunable properties remains a big challenge, and requires the development of a relatively simple design and facile accessibility of building blocks.