The potential ecotoxicity of nanosized zinc oxide (ZnO), synthesized by the polyol process, was investigated using common Anabaena flos-aquae cyanobacteria and Euglena gracilis euglenoid microalgae. The photosynthetic activities of these microorganisms, after addition of ZnO nanoparticles, varied with the presence of protective agents such as tri-n-octylphosphine oxide (TOPO) and polyoxyethylene stearyl ether (Brij-76) used to control particle size and shape during the synthesis. In the case of Anabaena flos-aquae , the photosynthetic activity, after addition of ZnO, ZnO-TOPO, and ZnO-Brij-76, decreased progressively due to stress induced by the presence of the nanoparticles in the culture medium. After contact with ZnO-TOPO nanoparticles, this decrease was followed by cell death. On the other hand, after 10 days, a progressive increase of the photosynthetic activity was observed after contact with ZnO and ZnO-Brij-76 nanoparticles. In the case of Euglena gracilis , cell death was observed after contact with all nanoparticles. Transmission electron microscopy (TEM) analyses of ultrathin sections of microorganisms showed that polysaccharides produced by Anabaena flos-aquae avoid particle internalization after contact with ZnO and ZnO-Brij-76 nanoparticles. On the other hand, nanoparticle internalization was observed after contact with all nanoparticles in the presence of Euglena gracilis and also with ZnO-TOPO nanoparticles after contact with Anabaena flos-aquae .
Common Anabaena, Calothrix, and Leptolyngbya cyanobacteria are shown to form Au, Ag, Pd, and Pt nanoparticles of well-controlled size. These nanoparticles are synthesized intra-cellularly, and naturally released in the culture medium, where they are stabilized by algal polysaccharides, allowing their easy recovery. The size of the recovered particles as well as the reaction yield is shown to depend on the cyanobacteria genus. Investigations of nanoparticle formation indicate that the intracellular nitrogenase enzyme is responsible for the metal reduction but that the cellular environment is involved in the colloid growth process.
Shell nacre (mother of pearl) of Pinctada margaritifera was analyzed by scanning electron microscopy. The originality of this work concerns the sampling performed to observe incipient nacre on the mantle side. The whole animal is embedded in methyl methacrylate followed by separation of the shell from the hardened mantle. It is revealed this way how each future nacre layer pre-exists as a film or compartment. Experimental observations also show for the first time, the progressive lateral crystallization inside this film, finishing under the form of a non-periodic pattern of polygonal tablets of bio-aragonite. It is evidenced that nuclei appear in the film in the vicinity of the zone where aragonite tablets of the underlying layer get in contact to each other. A possible explanation is given to show how nucleation is probably launched in time and space by a signal coming from the underlying layer. Finally, it is evidenced that tablets form a Voronoi tiling of the space: this suggests that their growth is controlled by an "aggregation-like" process of "crystallites" and not directly by the aragonite lattice growth.
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