We report the shape and size control of polyhedral gold nanocrystals by a modified polyol process. The rapid reduction of gold precursors in refluxing 1,5-pentanediol has successfully provided a series of gold nanocrystals in the shape of octahedra, truncated octahedra, cuboctahedra, cubes, and higher polygons by incremental changes of silver nitrate concentration. All nanocrystals were obtained quantitatively and were uniform in shape and size in the range of approximately 100 nm. Smaller octahedra and cubes were also prepared by using large amounts of PVP. Silver species generated from AgNO3 seemed to determine the final nanocrystal morphology by the selective growth of {111} and/or the restriction of {100}. The shape evolution of the particles was addressed by quenching the reactions at different time intervals. The approximately 60 nm seeds were generated rapidly and grown slowly with simultaneous edge sharpening. Aging the reaction mixture focused the size and shape of the nanocrystals by Ostwald ripening. We believe that our selective growth conditions can be applied to other shapes and compositions of face-centered cubic metals.

Polyhedral gold nanocrystals with decahedral, icosahedral, and truncated tetrahedral shapes are synthesized by a simple one-pot polyol process in the prescence of poly(vinyl pyrrolidone) (PVP). High PVP concentration up to 360 equiv of the gold precursor, HAuCl 4 , effectively stabilizes decahedral seeds to yield uniform decahedra with various edge sizes. Decreased PVP concentration subsequently leads to selective formation of icosahedra and truncated tetrahedra. This results from a combination between the relative energy difference of the polyhedral structures and the oxidative etching rate of the seeds by Cl -/O 2 during the reaction. The distinct morphologies of gold nanocrystals exhibit characteristic extinction patterns in the UV-vis-NIR ranges, and these properties are successfully analyzed by the discrete dipole approximation (DDA) calculation. Most extinctions stem from the polar and azimuthal dipolar excitations, and azimuthal quardrupole resonance appears between two dipolar bands in the 88-nm decahedra. Given these shape-and size-dependent optical properties, gold nanocrystals hold considerable promise for biomedical and photonic applications.

SUMMARY Tools capable of imaging and perturbing mechanical signaling pathways with fine spatiotemporal resolution have been elusive despite their importance in diverse cellular processes. The challenge in developing a mechanogenetic toolkit (i.e. selective and quantitative activation of genetically encoded mechanoreceptors) stems from the fact that many mechanically-activated processes are localized in space and time, yet additionally require mechanical loading to become activated. To address this challenge, we synthesized magnetoplasmonic nanoparticles that can image, localize, and mechanically load targeted proteins with high spatiotemporal resolution. We demonstrate their utility by investigating the cell surface activation of two mechanoreceptors: Notch and E-cadherin. By measuring cellular responses to a spectrum of spatial, chemical, temporal, and mechanical inputs at the single molecule and single cell level, we reveal how spatial segregation and mechanical force cooperate to direct receptor activation dynamics. This generalizable technique can be used to control and understand diverse mechanosensitive processes in cell signaling.

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Precise control over interfacial chemistry between nanoparticles and other materials remains a significant challenge limiting the broad application of nanotechnology in biology. To address this challenge, we use “Steric Exclusion” to completely convert commercial quantum dots (QDs) into monovalent imaging probes by wrapping the QD with a functionalized oligonucleotide. We demonstrate the utility of these QDs as modular and non-perturbing imaging probes by tracking individual Notch receptors on live cells.

An asymmetric single hollow structure was generated from Ag-Au-Ag heterometal nanorods by a partial galvanic replacement reaction for the first time. The C(2)-symmetry breaking took place because of the random generation of a single pit on only one end of the silver domain at an early stage of the reaction. Careful control of the reaction kinetics could also yield a double-hollow structure on both ends of the silver domain. The resulting single- and double-hollow nanorods exhibited characteristic extinctions in the near-IR range.

Morphology control of gold nanocrystals has been widely investigated following the first report that the optical properties of nonspherical gold nanoparticles are extremely dependent on their size and shape. [1] In principle, high-symmetry structures can feasibly be generated in a face-centered cubic lattice system when the R value, defined as the ratio of relative growth rates along {100} and {111}, is regulated precisely.[2] In the case of silver, poly(vinyl pyrrolidone), PVP, a surface-regulating agent, is proposed to be selectively bound on the {100} faces, and promotes directed growth of planes other than {100} to form silver cubes and nanowires. [3] However, the synthetic methodology for a certain shape is not readily applicable to other structures, because the different faces of the metal nanocrystals are distinguishable only within a narrow range of reaction conditions.[4] Recently, it was found that underpotential deposition (UPD) could account for gold nanorod formation when silver ions are added to the reaction mixture.[5] We also introduced Ag + ions to gold polyhedron synthesis and obtained regular shapes from octahedral to cubic in high yields.[6] It is anticipated that such a Au/Ag + UPD system can be employed as a general tool for directed growth of {111} faces, whereas addition of Au 3+ enhances {100} growth to stabilize the entire polyhedral structure. Herein, we applied this directed-growth approach to gold polyhedral seeds and observed complete shape conversion between cubes and octahedra. Recently, similar overgrowth strategies were reported for the synthesis of gold [7] and palladium [8] nanocrystals. We also synthesized cubes, cuboctahedra, and octahedra in high yields from small and large spherical seeds and analyzed their optical properties by discrete dipole approximation (DDA) calculations.Octahedral and cubic gold seeds were synthesized by a modified polyol process in boiling 1,5-pentanediol (PD), as reported previously.[6] The seed solutions in ethanol were transferred to PD and were set to 0.025 m with respect to the concentration of the gold precursor. For conversion of octahedra to cubes, AgNO 3 was added to boiling PD prior to adding the gold precursor. The solution of octahedral seed was introduced, and PVP and HAuCl 4 solutions were then added periodically over 7.5 min, followed by refluxing the mixture for 1 h. The scanning electron microscopy (SEM) image in Figure 1 b shows uniform octahedral seeds with an average edge length of 100 nm. As the reaction proceeded, the shape of the seeds changed from octahedral to truncated octahedral, cuboctahedral, and finally perfect cubic (see the Supporting Information). The resulting cubes have relatively sharp edges with an average length of 144 AE 14 nm (Figure 1 c), which corresponds to the length of an ideal cube ( p 2 100 nm) produced by exclusive {111} surface growth from the original octahedral structure. X-ray diffraction (XRD) data also reveal evolution of the {100} surface from [*] Prof.

Plasmonic nanostructures such as gold nanoparticles are very useful for monitoring chemical reactions because their optical properties are highly dependent upon the environment surrounding the particle surface. Here, we designed the catalytic structure composed of platinized cadmium sulfide with gold domains as a sensitive probe, and we monitored the photocatalytic decomposition of lactic acid to generate hydrogen gas in situ by single-particle dark-field spectroscopy. The plasmon band shift of the gold probe throughout the reaction exhibits significant particle-to-particle variation, and by simulating the reaction kinetics, the rate constant and structural information (including the diffusion coefficient through the shell and the relative arrangement of the active sites) can be estimated for individual catalyst particles. This approach is versatile for the monitoring of various heterogeneous reactions with distinct components at a single-particle level.