Gonzalez-Rubio, Guillermo

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Quantification of the Helical Morphology of Chiral Gold Nanorods

2022, Heyvaert, Wouter, Pedrazo-Tardajos, Adrián, Kadu, Ajinkya, Claes, Nathalie, Gonzalez-Rubio, Guillermo, Liz-Marzán, Luis M., Albrecht, Wiebke, Bals, Sara

Chirality in inorganic nanoparticles and nanostructures has gained increasing scientific interest, because of the possibility to tune their ability to interact differently with left- and right-handed circularly polarized light. In some cases, the optical activity is hypothesized to originate from a chiral morphology of the nanomaterial. However, quantifying the degree of chirality in objects with sizes of tens of nanometers is far from straightforward. Electron tomography offers the possibility to faithfully retrieve the three-dimensional morphology of nanomaterials, but only a qualitative interpretation of the morphology of chiral nanoparticles has been possible so far. We introduce herein a methodology that enables us to quantify the helicity of complex chiral nanomaterials, based on the geometrical properties of a helix. We demonstrate that an analysis at the single particle level can provide significant insights into the origin of chiroptical properties.

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Micelle-directed chiral seeded growth on anisotropic gold nanocrystals

2020, Gonzalez-Rubio, Guillermo, Mosquera, Jesús, Kumar, Vished, Pedrazo-Tardajos, Adrián, Llombart, Pablo, Solís, Diego M., Lobato, Ivan, Noya, Eva G., Liz-Marzán, Luis M., Bals, Sara

Surfactant-assisted seeded growth of metal nanoparticles (NPs) can be engineered to produce anisotropic gold nanocrystals with high chiroptical activity through the templating effect of chiral micelles formed in the presence of dissymmetric cosurfactants. Mixed micelles adsorb on gold nanorods, forming quasihelical patterns that direct seeded growth into NPs with pronounced morphological and optical handedness. Sharp chiral wrinkles lead to chiral plasmon modes with high dissymmetry factors (~0.20). Through variation of the dimensions of chiral wrinkles, the chiroptical properties can be tuned within the visible and near-infrared electromagnetic spectrum. The micelle-directed mechanism allows extension to other systems, such as the seeded growth of chiral platinum shells on gold nanorods. This approach provides a reproducible, simple, and scalable method toward the fabrication of NPs with high chiral optical activity.

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Controlled Alloying of Au@Ag Core–Shell Nanorods Induced by Femtosecond Laser Irradiation

2021, Gonzalez-Rubio, Guillermo, Díaz-Núñez, Pablo, Albrecht, Wiebke, Manzaneda‐González, Vanesa, Bañares, Luis, Rivera, Antonio, Liz-Marzán, Luis M., Peña-Rodríguez, Ovidio, Bals, Sara, Guerrero-Martínez, Andrés

Bimetallic nanoparticles display unique physical and chemical properties, including improved chemical stability, enhanced optical properties, or higher catalytic activity. Here, a synthetic methodology is described to obtain bimetallic heterostructures and alloyed plasmonic nanocrystals through the irradiation of colloidal Au@Ag core–shell nanorods (Au@Ag NRs) with femtosecond laser pulses. Depending on the energy deposited on the Au@Ag NRs, different morphologies and degrees of alloying are obtained, such as hot-dog-like and rice-like (partially alloyed) NRs, as well as fully alloyed nanospheres. By using advanced electron microscopy techniques and energy-dispersive X-ray spectroscopy (EDX) tomography, both the morphology and the elemental distribution of the irradiated nanoparticles can be disclosed, and correlated to detailed investigations of their optical properties using electromagnetic simulations. The wide variety of bimetallic species provided by the proposed approach is a clear indication of the potential of combining synthetic colloidal methods with fs-pulsed laser irradiation for the fabrication of unique multielemental nanoparticles. The resulting control over size and composition raises promising prospects for catalytic, plasmonic, and magnetic applications of multimetallic nanocrystals.

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Disconnecting Symmetry Breaking from Seeded Growth for the Reproducible Synthesis of High Quality Gold Nanorods

2019-04-23, Gonzalez-Rubio, Guillermo, Kumar, Vished, Llombart, Pablo, Díaz-Núñez, Pablo, Bladt, Eva, Altantzis, Thomas, Bals, Sara, Peña-Rodríguez, Ovidio, Guerrero-Martínez, Andrés, Liz-Marzán, Luis M.

One of the major difficulties hindering the widespread application of colloidal anisotropic plasmonic nanoparticles is the limited robustness and reproducibility of multistep synthetic methods. We demonstrate herein that the reproducibility and reliability of colloidal gold nanorod (AuNR) synthesis can be greatly improved by disconnecting the symmetry-breaking event from the seeded growth process. We have used a modified silver-assisted seeded growth method in the presence of the surfactant hexadecyltrimethylammonium bromide and n-decanol as a co-surfactant to prepare small AuNRs in high yield, which were then used as seeds for the growth of high quality AuNR colloids. Whereas the use of n-decanol provides a more-rigid micellar system, the growth on anisotropic seeds avoids sources of irreproducibility during the symmetry breaking step, yielding uniform AuNR colloids with narrow plasmon bands, ranging from 600 to 1270 nm, and allowing the fine-tuning of the final dimensions. This method provides a robust route for the preparation of high quality AuNR colloids with tunable morphology, size, and optical response in a reproducible and scalable manner.

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Surfactant‐Assisted Symmetry Breaking in Colloidal Gold Nanocrystal Growth

2020-05, Gonzalez-Rubio, Guillermo, Scarabelli, Leonardo, Guerrero-Martínez, Andrés, Liz-Marzán, Luis M.

Colloidal anisotropic gold nanocrystals play a central role in the field of plasmonics owing to their tunable optical activity across a wide spectral range. However, achieving sufficient optical quality for practical implementation requires advanced synthetic protocols yielding gold nanocrystals with the desired morphology and plasmonic properties. This Minireview focuses on a fundamental step during the growth of anisotropic nanocrystals, namely symmetry breaking. In connection with thermodynamic and kinetic control of nanocrystal growth, we discuss the complex interplay between the role of seed morphology and that of surfactants, shape‐directing additives and reducing agents. We revisit some iconic syntheses of anisotropic gold nanoparticles, including nanorods, nanotriangles, and nanobipyramids. Finally, we analyze the use of co‐surfactants as an emerging strategy to disconnect the symmetry breaking event from the anisotropic growth process, overcoming current limitations in the synthesis of anisotropic gold nanocrystals.

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Peptides used to make light-twisting nanoparticles

2018, Gonzalez-Rubio, Guillermo, Liz-Marzán, Luis M.