All news – Inorganic Nanoparticles Group

Hollow PdAg-CeO2 heterodimer nanocrystals as highly structured heterogeneous catalysts

Editor — Mon, 13 Jan 2020 13:49:54 +0000

In the present work, hollow PdAg-CeO₂ heterodimer nanocrystals (NCs) were prepared and tested as catalysts for the selective hydrogenation of alkynes. These nanostructures combine for the first time the beneficial effect of alloying Pd with Ag in a single NC hollow domain with the formation of active sites at the interface with the CeO₂ counterpart in an additive manner. The PdAg-CeO₂ NCs display excellent alkene selectivity for aliphatic alkynes. For the specific case of hydrogenation of internal alkynes such as 4-octyne, very low over-hydrogenation and isomerization products were observed over a full conversion regime, even after prolonged reaction times. These catalytic properties were remarkably superior in comparison to standard catalysts. The promotion of Ag on the moderation of the reactivity of the Pd phase, in combination with the creation of interfacial sites with the CeO₂ moiety in the same nanostructure, is pointed as the responsible of such a remarkable catalytic performance.

Scientific Reports volume 9, Article number: 18776 (2019)

Seeded-Growth Aqueous Synthesis of Colloidal-Stable Citrate-Stabilized Au/CeO2 Hybrid Nanocrystals: Heterodimers, Core@Shell, and Clover- and Star-Like Structures

Editor — Mon, 13 Jan 2020 13:46:57 +0000

Well-defined colloidal-stable citrate-stabilized Au/CeO₂ hybrid nanocrystals (NCs) with coherent quasi-epitaxial interfaces and unprecedented control of their architectural and morphological characteristics have been synthesized via a novel and straightforward seeded-growth aqueous approach. The synthetic strategy, based on the identification of the experimental conditions under which the heterogeneous nucleation and growth processes of CeO₂ onto presynthesized Au are controlled, allows for the fine adjustment of each individual domain in the structure, particularly the size of the Au core (from 5 to 100 nm), the thickness of the CeO₂ shell (from 5 to 20 nm), and the growth mode of CeO₂ onto Au NCs (from core@shell to heterodimer, clover- and star-like structures). This morphological control is achieved by the rational use of sodium citrate, which plays multiple key roles, as a reducer and stabilizing agent in the preparation of Au NCs, and as a complexing agent of Ce³⁺ for its controlled oxidation and hydrolysis during the subsequent CeO₂ deposition. The resultant Au/CeO₂ NCs remain stable and well-dispersed in water, allowing us to study the impact of fine variations of the NC structure on the underlying optical response. This level of morphological control, as well as the ease by which such well-defined nanostructures are produced, opens new opportunities for systematically investigating the interactions between individual components in designing more advanced complex NCs. Remarkably, because no organic solvents are used and no toxic waste is formed during the reaction, the proposed synthesis method can be defined as sustainable, viable, and cost-effective.

Chem. Mater. 2019, 31, 19, 7922-7932

Robust one-pot synthesis of citrate-stabilized Au@CeO2 hybrid nanocrystals with different thickness and dimensionality

Editor — Wed, 15 May 2019 09:25:46 +0000

Well-defined colloidal Au@CeO₂ hybrid nanocrystals (NCs) comprising different core/shell morphologies have been synthesized via a novel and simple one-pot aqueous approach. The method allows producing hybrid morphologies composed by an active and accessible Au core coated by a porous CeO₂ shell with varying shell thickness and dimensionality by simply adjusting the Au³⁺/Ce³⁺ precursor ratio. These hybrid NCs are highly monodisperse and well-dispersed in water, showing intense surface plasmon resonance bands that offer unique opportunities for advanced material applications, such as plasmonics and catalysis.

Robust one-pot synthesis of citrate-stabilized Au@CeO2 hybrid nanocrystals with different thickness and dimensionality

Volume 15, June 2019, Pages 445-452

Tunable electrochemistry of gold-silver alloy nanoshells

Editor — Wed, 15 May 2019 09:23:30 +0000

The widespread and increasing interest in enhancing biosensing technologies by increasing their sensitivities and lowering their costs has led to the exploration and application of complex nanomaterials as signal transducers and enhancers. In this work, the electrochemical properties of monodispersed AuAg alloy nanoshells (NSs) with finely tunable morphology, composition, and size are studied to assess their potential as electroactive labels. The controlled corrosion of their silver content, caused by the oxidizing character of dissolved oxygen and chlorides of the electrolyte, allows the generation of a reproducible electrochemical signal that is easily measurable through voltammetric techniques. Remarkably, the underpotential deposition of dissolved Ag⁺ catalyzed on AuAg NS surfaces is observed and its dependence on the nanoparticle morphology, size, and elemental composition is studied, revealing a strong correlation between the relative amounts of the two metals. The highest catalytic activity is found at Au/Ag ratios higher than ≈ 10, showing how the synergy between both metals is necessary to trigger the enhancement of Ag⁺ reduction. The ability of AuAg NSs to generate an electrocatalytic current without the need for any strong acid makes them an extremely promising material for biosensing applications.

Tunable electrochemistry of gold-silver alloy nanoshells

Nano Research

December 2018, Volume 11, Issue 12, pp 6336–6345

Size-Dependent Protein–Nanoparticle Interactions in Citrate-Stabilized Gold Nanoparticles: The Emergence of the Protein Corona. Published in Bioconjugate Chemistry

Editor — Fri, 28 Sep 2018 13:05:06 +0000

Surface modifications of highly monodisperse citrate-stabilized gold nanoparticles (AuNPs) with sizes ranging from 3.5 to 150 nm after their exposure to cell culture media supplemented with fetal bovine serum were studied and characterized by the combined use of UV−vis spectroscopy, dynamic light scattering, and zeta potential measurements. In all the tested AuNPs, a dynamic process of protein adsorption was observed, evolving toward the formation of an irreversible hard protein coating known as Protein Corona. Interestingly, the thickness and density of this protein coating were strongly dependent on the particle size, making it possible to identify different transition regimes as the size of the particles increased: (i) NP-protein complexes (or incomplete corona), (ii) the formation of a near-single dense protein corona layer, and (iii) the formation of a multilayer corona. In addition, the different temporal patterns in the evolution of the protein coating came about more quickly for small particles than for the larger ones, further revealing the significant role that size plays in the kinetics of this process. Since the biological identity of the NPs is ultimately determined by the protein corona and different NP−biological interactions take place at different time scales, these results are relevant to biological and toxicological studies.

Size-Dependent Protein–Nanoparticle Interactions in Citrate-Stabilized Gold Nanoparticles: The Emergence of the Protein Corona.

Jordi Piella, Neus G. Bastus, and Víctor Puntes Bioconjugate Chem., 2017, 28 (1), pp 88–97

Time- and Size-Resolved Plasmonic Evolution with nm Resolution of Galvanic Replacement Reaction in AuAg Nanoshells Synthesis. Published in Chemistry of Materials

Editor — Fri, 28 Sep 2018 12:18:39 +0000

The rational design of advanced nanomaterials with enhanced optical properties can be reached only with the profound thermodynamic and kinetic understanding of their synthetic processes. In this work, the synthesis of monodisperse AuAg nanoshells with thin shells and large voids is achieved through the development of a highly reproducible and robust methodology based on the galvanic replacement reaction. This is obtained thanks to the systematic identification of the role played by the different synthetic parameters involved in the process (such as surfactants, co-oxidizers, complexing agents, time, and temperature), providing an unprecedented control over the material’s morphological and optical properties. Thus, the time- and size-resolved evolution of AuAg nanoshells surface plasmon resonance band is described for 15, 30, 60, 80, 100, and 150 nm-sized particles spanning almost through the entire visible spectrum. Its analysis reveals a four-phase mechanism coherent with the material’s morphological transformation. Simulations based on Mie’s theory confirm the observed optical behavior in AuAg nanoshells formation and provide insights into the influence of the Au/Ag ratio on their plasmonic properties. The high degree of morphological control provided by this methodology represents a transferable and scalable strategy for the development of advanced-generation plasmonic nanomaterials.

Time- and Size-Resolved Plasmonic Evolution with nm Resolution of Galvanic Replacement Reaction in AuAg Nanoshells Synthesis.

Lorenzo Russo , Florind Merkoçi, Javier Patarroyo , Jordi Piella, Arben Merkoçi , Neus G. Bastús , and Victor Puntes Chem. Mater., 2018, 30 (15), pp 5098–5107

Formation of the Protein Corona: The Interface between Nanoparticles and the Immune System. Published in Seminars in Immunology

Editor — Fri, 28 Sep 2018 11:14:42 +0000

The interaction of inorganic nanoparticles and many biological fluids often withstands the formation of a Protein Corona enveloping the nanoparticle. This Protein Corona provides the biological identity to the nanoparticle that the immune system will detect. The formation of this Protein Corona depends not only on the composition of the nanoparticle, its size, shape, surface state and exposure time, but also on the type of media, nanoparticle to protein ratio and the presence of ions and other molecular species that interfere in the interaction between proteins and nanoparticles. This has important implications on immune safety, biocompatibility and the use of nanoparticles in medicine.

Formation of the Protein Corona: The Interface between Nanoparticles and the Immune System

Nanosafety: Towards Safer Nanoparticles by Design. published in Current Medicinal Chemistry

Editor — Fri, 28 Sep 2018 11:05:36 +0000

The continuous development of Nanotechnology is progressively introducing nanoparticles into society. However, little is known about the safety of nanoparticles and functions of engineered nanomaterials, in particular how the physicochemical properties of the materials relate to mechanisms of injury at the nano-bio interface. While comprehensive knowledge on the potential toxicity of NPs is still lacking, as time goes by and research in the field continues, different aspects, such as interactions with the immune system, perturbation of cellular membranes, transportation of toxic moieties and others are emerging as potentially hazardous aspects of NPs. As a result, this rapidly advancing new field requires the development of novel test strategies based on the contribution of toxicological pathways to the pathophysiology of disease that allow complex toxicants to be screened in robust, mechanism-based assays in which the bulk of the investigation can be carried out at the cellular and biomolecular level whilst maintaining limited animal use. A review of these strategies will help to provide guidelines for synthetic nanochemists on how to design NPs to be safe during their full life cycle while maintaining their parental desired properties.

Nanosafety: Towards Safer Nanoparticles by Design. published in Current Medicinal Chemistry

Hollow metal nanostructures for enhanced plasmonics: synthesis, local plasmonic properties and applications. Published in Nanophotonics

Editor — Fri, 28 Sep 2018 10:09:28 +0000

Metallic nanostructures have received great attention due to their ability to generate surface plasmon resonances, which are collective oscillations of conduction electrons of a material excited by an electromagnetic wave. Plasmonic metal nanostructures are able to localize and manipulate the light at the nanoscale and, therefore, are attractive building blocks for various emerging applications. In particular, hollow nanostructures are promising plasmonic materials as cavities are known to have better plasmonic properties than their solid counterparts thanks to the plasmon hybridization mechanism. The hybridization of the plasmons results in the enhancement of the plasmon fields along with more homogeneous distribution as well as the reduction of localized surface plasmon resonance (LSPR) quenching due to absorption. In this review, we summarize the efforts on the synthesis of hollow metal nanostructures with an emphasis on the galvanic replacement reaction. In the second part of this review, we discuss the advancements on the characterization of plasmonic properties of hollow nanostructures, covering the single nanoparticle experiments, nanoscale characterization via electron energy-loss spectroscopy and modeling and simulation studies. Examples of the applications, i.e. sensing, surface enhanced Raman spectroscopy, photothermal ablation therapy of cancer, drug delivery or catalysis among others, where hollow nanostructures perform better than their solid counterparts, are also evaluated.

Hollow metal nanostructures for enhanced plasmonics: synthesis, local plasmonic properties and applications.

Probing the surface reactivity of nanocrystals by the catalytic degradation of organic dyes: the effect of size, surface chemistry and composition. Published in Journal of Materials Chemistry A

Editor — Fri, 28 Sep 2018 10:00:57 +0000

We herein present a comprehensive study on how the catalytic performance and reusability of Au nanocrystals (NCs) are affected by systematic variations of crystal size, surface coating and composition. The reductions of different organic dyes (4-nitrophenol, rhodamine B and methylene blue) by borohydride ions were used as model catalytic reactions. The catalytic performance of the Au NCs ranged between 3.6 to 110 nm was found to be dependent on crystal size, indicating that Au surface atoms have a distinct size-dependent reactivity in this reaction. Similarly, the catalytic performance was found to be strongly dependent on the nature of the coating molecule, obtaining lower catalytic activities for molecules strongly bound to the Au surface. Finally, the catalytic performance was found to be dependent on the chemical composition of the NC (Au, Ag, Pt) and the model dye used as a testing system, with the highest degradation rate found for methylene blue, followed by 4-nitrophenol and rhodamine B. We believe that this study provides a better understanding of the catalytic performance of Au NCs upon controlled modifications of the structural and morphological parameters, and a working environment that can be used to facilitate the selection of the optimum NC size, coating molecule and evaluation system for a particular study of interest.

Probing the surface reactivity of nanocrystals by the catalytic degradation of organic dyes: the effect of size, surface chemistry and composition