Procedures for the Synthesis and Capping of Metal Nanoparticles.

The increasing impact of metallic nanoparticles on life sciences has stimulated the development of new techniques and multiple improvements to the existing methods of manufacturing nanoparticles with tailored properties. Nanoparticles can be synthesized through a variety of physical and chemical methods. The choice of preparation procedure will depend on the physical and chemical characteristics required in the final product, such as size, dispersion, chemical miscibility, and optical properties, among others. Here we review basic practical procedures used for the preparation of protected and unprotected metallic nanoparticles and describe a number of experimental procedures based on colloidal chemistry methods. These include gold nanoparticle synthesis by reduction with trisodium citrate, ascorbic acid, or sugars in aqueous phase and nanoparticle passivation with alkanethiols, CTAB, or BSA. We also describe microwave-assisted synthesis, nanoparticle synthesis in ethylene glycol, and template-assisted synthesis with dendrimers, and, briefly, how to control nanoparticle shape (star-shaped and branched nanoparticles).

Pt-Ni/ZnO-rod catalysts for hydrogen production by steam reforming of methanol with oxygen.

Ni, Pt and a mixture of Ni and Pt supported on ZnO-rods were evaluated in autothermal steam reforming of methanol (ASRM) for hydrogen production as a function of the reaction temperature. The catalytic materials were characterized by SEM-EDS, XRD, TEM, HRTEM, TPR and BET. Analysis by SEM and TEM showed structural modifications on the surface of the ZnO rods after Ni impregnation. The reactivity of the catalytic materials in the range of 200-500 °C showed that the bimetallic sample had better catalytic activity among all the catalysts studied. This finding could be associated to PtZn and NiZn alloys present in this catalyst, which were identified by XRD and HRTEM analyses. Catalyst characterization by XRD after the catalytic testing showed that the intermetallic PtZn phase was stable during the reaction in the Pt/ZnO-rod sample. The cubic Ni0.75-Zn0.25 structure identified in the Ni/ZnO-rod sample was transformed to Zn0.1-Ni0.9-O and metallic Ni phases, respectively. On the bimetallic PtNi/ZnO-rod sample, the cubic Ni0.75-Zn0.25 structure remained, although the tetragonal NiZn structure is unstable and was destroyed during the ASRM reaction and then a new phase of Ni0.7Pt0.3 emerged. The promotion effect of Pt and/or Ni on the ZnO-rod was clearly shown.

Procedures for the synthesis and capping of metal nanoparticles.

The increasing impact of metallic nanoparticles in life sciences has stimulated the development of new techniques and multiple improvements of the existing methods of manufacturing nanoparticles with tailored properties. Nanoparticles can be synthesized through a variety of physical and chemical methods. The choice of preparation procedure will depend on the physical and chemical characteristics required on the final product, such as size, dispersion, chemical miscibility, optical properties, among others. Here we review basic practical procedures used for the preparation of protected and unprotected metallic nanoparticles and describe a number of experimental procedures based on colloidal chemistry methods. These include gold nanoparticle synthesis by reduction with trisodium citrate, ascorbic acid, or sugars in aqueous phase; nanoparticle passivation with alkanethiols, cetyltrimethylammonium bromide, or bovin serum albumin. We also describe microwave-assisted synthesis, nanoparticle synthesis in ethylene glycol, template-assisted synthesis with dendrimers and briefly describe how to control nanoparticle shape (star-shaped and branched nanoparticles).

Temperature effect on the synthesis of Au-Pt bimetallic nanoparticles.

Pt-Au bimetallic nanoparticles have been synthesized by the polyol method and stabilized with poly(vinylpyrrolidone) (PVP), modifying the temperature of synthesis. Interesting structure changes were observed in the nanoparticles as the temperature was varied. At lower temperatures no bimetallic nanoparticles were detected, but as the temperature increased bimetallic nanoparticles started to appear, commonly obtaining core-shell nanoparticles, always covered by the polymer. This originates the modification of the optical response of the system in the UV-visible region. An absorption peak centered at 520 nm at low temperatures was observed (100-110 degrees C); at higher temperatures (130-170 degrees C) there were non detectable absorption peaks, and finally at the two highest temperatures (180-190 degrees C) the reappearance of an absorption feature centered at 510 nm was noticed. These UV-visible results indirectly imply the composition of the surface of the particle. The structure of the particles has been determined using transmission electron microscopy and high-angle annular dark field (HAADF), the latter being a powerful technique to determine the structural composition of the particles and allowing a direct correlation of the optical response with their structural composition. X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies were also performed on the samples and their results support the idea of a Pt(core)-Au(shell) structure with the elements segregated from each other. The combination of these experimental techniques with calculated UV-vis absorption spectra allowed, in a reliable way, the elucidation of the nanoparticles structure and elemental distribution.

Noble-metal nanoparticles directly conjugated to globular proteins.

We report the synthesis of gold nanoparticles directly conjugated to bovine serum albumin protein by chemical reduction in aqueous solution. Transmission electron microscopy reveals that the gold nanoparticles are well dispersed with an average diameter less than 2 nm, and elemental analysis verifies the composition of the gold-protein conjugates. Infrared spectroscopy confirms that the polypeptide backbone is not cleaved during the conjugation process and that the side chain functional groups remain intact. Raman spectroscopy demonstrates that the disulfide bonds in the conjugated protein are broken and thus are available for interaction with the nanoparticle surface. This synthesis method is a new technique for directly attaching gold nanoparticles to macromolecular proteins.