Examinando por Autor "Obelleiro-Liz, Manuel"

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Additive-Free Synthesis of (Chiral) Gold Bipyramids from Pentatwinned Nanorods
(American Chemical Society, 2024-10-17) Bevilacqua, Francisco; Girod, Robin; Martin, Victor F.; Obelleiro-Liz, Manuel; Vinnacombe-Willson, Gail A.; Van Gordon, Kyle; Hofkens, Johan; Taboada, Jose M.; Bals, Sara; Liz-Marzán, Luis M.
The production of colloidal metal nanostructures with complex geometries usually involves shape-directing additives, such as metal ions or thiols, which stabilize high-index facets. These additives may however affect the nanoparticles’ surface chemistry, hindering applications, e.g., in biology or catalysis. We report herein the preparation of gold bipyramids with no need for additives and shape yields up to 99%, using pentatwinned Au nanorods as seeds and cetyltrimethylammonium chloride as surfactant. For high-growth solution:seed ratios, the bipyramids exhibit an unusual “belted” structure. Three-dimensional electron microscopy revealed the presence of high-index {117}, {115}, and {113} side facets, with {113} and {112} facets at the belt. Belted bipyramids exhibit strong near-field enhancement and high extinction in the near-infrared, in agreement with electromagnetic simulations. These Ag-free bipyramids were used to seed chiral overgrowth using 1,1′-binaphthyl-2,2′-diamine as a chiral inducer, with g-factor up to 0.02, likely the highest reported for bipyramid seeds so far.
Influence of Geometrical Parameters on the Optical Activity of Chiral Gold Nanorods
(Wiley, 2023-03-08) Obelleiro-Liz, Manuel; Martin, Victor F.; Solis, Diego M.; Taboada, Jose M.; Obelleiro, Fernando; Liz-Marzán, Luis M.
Chiral metal nanoparticles (NPs) offer a powerful means of inducing and harnessing optical activity. However, due to the incomplete knowledge of the underlying growth mechanisms, there is still limited control over the achievable morphological detail and, consequently, over the resulting optical activity. Therefore, theoretical modeling is needed to guide experimental development toward optimizing the plasmonic chiroptical response. Toward filling this gap, herein an extensive parametric analysis is presented, via computer-aided-design (CAD) models and full-wave electrodynamic simulations, which aims at systematically analyzing the influence of structural changes on the plasmonic circular dichroism (CD) spectra of rod-shaped gold NPs comprising helical indentations on achiral nanorod cores. From this analysis, interesting patterns in the plasmon-mediated resonant behavior are identified and cause–effect relationships are drawn that may serve as a go-to recipe for the understanding and fabrication of these NPs and their applications, such as spectroscopic (bio)detection including CD spectral shifts and surface-enhanced Raman optical activity.