Nanoparticle formation in giant vesicles: synthesis in biomimetic compartments.

The formation of inorganic nanomaterials such as CdS, ZnS, and gold and silver nanoparticles was recently observed in microorganisms. The underlying processes are still not well understood at the molecular scale. It has been proposed that enzymes or peptides may take part in the nucleation and reaction control. It seems highly desirable to perform similar reactions in artificial systems as a first step towards biomimetic fabrication. Here, we introduce two novel protocols for nanoparticle synthesis in such artificial systems provided by giant vesicles. These membrane compartments have two main advantages. First, individual compartments can be manipulated by electric fields, micropipettes, or optical tweezers. Second, the particle formation process can be directly monitored using different microscopy techniques. Our protocols are based on the controlled fusion of such vesicles and on their adhesion via nanotubes. When these two protocols are applied to the synthesis of CdS nanoparticles, the particle size can be tuned to be 4 or 50 nm, which is in the range of quantum dot sizes. Our results show that controlled changes in the structure and topology of membrane compartments can be used to synthesize nanoparticles even in the absence of inorganic binding peptides. Cells and microorganisms have been reported to have the amazing ability to synthesize inorganic nanoparticles. The tentative interpretation of this observation is related to the involvement of specific molecules such as inorganicbinding peptides, which are also developed commercially to control nanoparticle synthesis in artificial cell-free reaction systems. In contrast to biochemistry-based cell-assisted synthesis, our present study aims at identifying mechanisms of nanomaterial synthesis in confined compartments provided by model biomembranes.