Seed-mediated growth of gold nanoparticles using self-assembled monolayer of polystyrene microspheres as nanotemplate arrays

Arrays of noble metal nanoparticles show potential applications in （bio-）sensing, optical storage, surface-enhanced spectroscopy, and waveguides. For all such potential devices, controlling the size, morphology, and interparticle spacing of the nanoparticles is very important. Here, we combine seed-mediated growth with nanosphere lithography to study the controllable growth of gold nanoparticles （Au NPs）, in which the self-assembly monolayer of polystyrene （PS） on a silicon surface is used to guide the modification of allaunesilanes and the subsequent adsorption of gold seeds; seed-mediated growth is applied to controlling the morphology and size of Au NPs. The size of adsorption region （determining the number of adsorbed gold seeds） is controlled by etching PS microspheres with oxygen plasma or annealing PS microspheres at the glass transition temperature. The size and morphology of the Au NPs are controlled by changing growth conditions. In such a way, we have achieved the dual control of the obtained Au NPs. Preliminary results show that this strategy holds a great promise. This approach can also be extended to a wide range of materials and substrates.

Preparation of large In(OH)3 and In2O3 particles through a seed-mediated growth method in a microreactor

Indium hydroxide(ln(OH)3)and indium oxide(ln2O3)particles are typically synthesized through chemical precipitation methods.In this study,we used a seed-mediated growth method and microreactor-based synthesis process.We synthesized cubic In(OH)3 particles with a crystal size of 172 nm from an 5%(w/v)indium chloride solution.The In2O3 particles synthesized through the thermal decomposition of In(OH)3 particles featured crystals up to 90 nm in size with an average size of 73 nm,which were much larger than the 20-30 nm In2O3 particles synthesized by a traditional precipitation method.The concentrations of the seed and growth solutions were varied from 1%to 7%(w/v).The crystal size of the particles increased with the concentration of the seed and growth solutions;this tendency was the opposite to that observed for the precipitation method.Through the use of a 5%(w/v)seed solution,the flow rate of the growth solution was varied from 1 to 10mL/min,and the resulting crystal size decreased as the flow rate was increased.To understand the reasons for this trend,the growth rate of the crystals was determined at different flow rates(i.e.,1,5,and 10 mL/min).A growth model consistent with the experimental results was established,which demonstrated that slow addition of the growth solution was beneficial for preparing large indium hydroxide particles.

A Comparative Investigation of Dye-Sensitized Titanium Dioxide(TiO_2) Nanorods Grown on Indium Tin Oxide(ITO) Substrates by Direct and Seed-Mediated Hydrothermal Methods

We report a comparative investigation of the characteristics of modified TiO2 nanorods grown on conducting indium tin oxide glass （/TO） substrates by two different hydrothermal methods： the direct method by which rutile TiOa nanorods were grown directly on plain ITO substrates and the seed-mediated one using which a thin film of anatase TiO2 seed layer was laid down by spin coating and annealing prior to the growth of TiO2 nanorods on it. Microstructural analysis of the samples using X-ray diffraction confirmed their rutile nature. The average crystallite size estimated using Scherrer＇s formula was found to fall in the range of 11-17 nm in both cases. Field emission scanning electron microscopy revealed the nanorod morphologies of a dandelion arrangement in the case of directly grown ones and a proper vertical orientation in the case of the seed-mediated method. UV-Vis spectroscopy analysis of both the samples exhibited redshifts with intense absorption of visible radiation, and the seed-mediated one was found to possess an increased bandgap. The transport nature of the samples was characterized by significant increase in both dark and photocurrents. The results show that the dark and photocurrent values of the directly grown TiO2 nanorods were greater than those of the seed-mediated ones by - seven and five folds, respectively, and therefore, it could serve as efficient photoelectrodes in dye-sensitized solar cells.

Preparation of Gold Nanorods of High Quality and High Aspect Ratio

We report the synthesis of gold nanorods （NRs） by seed-mediated growth method. A small amount of different shapes such as triangles, hexagons and a large amount of rods are obtained by varying the proportion of seed to metal salt, adding NaOH to growth solution as well as using the seed solution of CTAB-capped agent. The gold nanorod （NR） formation yield is improved. Meanwhile, the growth mechanism of high yield gold NRs is discussed. The high quality single size NRs can be separated from polydisperse samples using surfactant-assisted nanorod self-assembly. The gold NRs synthesized were characterized by transmission electron microscopy （TEM） and UV-vis spectroscopy.

Engineering surface strain for site-selective island growth of Au on anisotropic Au nanostructures

Controlled growth of islands on plasmonic metal nanoparticles represents a novel strategy in creating unique morphologies that are difficult to achieve by conventional colloidal synthesis processes,where the nanoparticle morphologies are typically determined by the preferential development of certain crystal facets.This work exploits an effective surface-engineering strategy for site-selective island growth of Au on anisotropic Au nanostructures.Selective ligand modification is first employed to direct the site-selective deposition of a thin transition layer of a secondary metal,e.g.,Pd,which has a considerable lattice mismatch with Au.The selective deposition of Pd on the original seeds produces a high contrast in the surface strain that guides the subsequent site-selective growth of Au islands.This strategy proves effective in not only inducing the island growth of Au on Au nanostructures but also manipulating the location of grown islands.By taking advantage of the iodide-assisted oxidative ripening process and the surface strain profile on Au nanostructures,we further demonstrate the precise control of the islands’number,coverage,and wetting degree,allowing fine-tuning of nanoparticles’optical properties.

Core-shell gold-copper nanoparticles:Evolution of copper shells on gold cores at different gold/copper precursor ratios

Core-shell nanostructures usually exhibit tunable catalytic properties in comparison with their single core or shell counterpart due to electronic interaction and lattice strain between the core and shell regions.Herein,we report the intriguing evolution of copper(Cu)shells on the gold(Au)cores at different Au/Cu precursor ratios during the synthesis of core-shell Au-Cu nanoparticles at an organic medium via seed-mediated growth method.In brief,at relatively low Cu ratios,quasi-spherical Au-Cu nanoparticles with conventional core-shell structures are the majority products,in which the Cu shell thickness increases with the increase of Cu precursor ratios.The dif-ference is that at high Cu ratios,the Cu shells no longer increase their thickness,but evolve into a dendritic structure.Interestingly,the core-shell Au-Cu nanoparticles with dendritic Cu shells could be transformed into interesting Au-Cu cage-bell structures after a ripening process at elevated temperature.Further,through galvanic replacement reaction with Pt precursors,the thin Cu shells could be converted into CuPt alloy shells on the Au cores,which exhibit enhanced activity towards methanol oxidation reaction with satisfactory durability,in comparison with that of commercial Pt/C catalysts.

Mesoflowers:A New Class of Highly Effi cient Surface-Enhanced Raman Active and Infrared-Absorbing Materials

A method for the synthesis of a new class of anisotropic mesostructured gold material,which we call“mesoflowers”,is demonstrated.The mesoflowers,unsymmetrical at the single particle level,resemble several natural objects and are made up of a large number of stems with unusual pentagonal symmetry.The mesostructured material has a high degree of structural purity with star-shaped,nano-structured stems.The mesoflowers were obtained in high yield,without any contaminating structures and their size could be tuned from nano-to meso-dimensions.The dependence of various properties of the mesoflowers on their conditions of formation was studied.The near-infrared infrared(NIR IR)absorption exhibited by the mesoflowers has been used for the development of infrared filters.Using a prototypical device,we demonstrated the utility of the gold mesoflowers in reducing the temperature rise in an enclosure exposed to daylight in peak summer.These structures showed a high degree of surface-enhanced Raman scattering(SERS)activity compared to spherical analogues.SERS-based imaging of a single mesoflower is demonstrated.The high SERS activity and NIR IR absorption property open up a number of exciting applications in diverse areas.

Gene deletor： a new tool to address gene flow and food safety concerns over transgenic crop plants

Environmental and food safety concerns over transgenic plants have hampered commercial applications of transgenic plant technology worldwide. A recently developed transgene deletion technology, named gene deletor technology, may be used to eliminate all transgenes from pollen, seeds, fruits or other organs when functions of transgenes are no longer needed or their presence may cause concerns. In this review, I will briefly describe the principle of the gene deletor technology with major supporting experimental data. I will also explain main characteristics and requirements of the gene deletor technology. Finally, I will discuss the gene deletor technology in the context of how it may be used to alleviate environmental and food safety concerns over transgenic plants in vegetatively and sexually propagated plants, to prevent volunteer transgenic plants, to protect proprietary transgenic technologies, and to allow farmers to reuse their harvested seeds for future planting.