Search

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., We acknowledge financial support from the Spanish MINECO (MAT2015-70725-R, ENE2017-85087-C3), MICINN (RTI2018-099965-B-I00), and from the Catalan Agencia de Gestió d’Ajuts Universitaris i de Recerca (AGAUR) (2017-SGR-1431, 2017-SGR-327). Financial support from the HISENTS (685817) Project financed by the European Community under H20202 Capacities Programme is gratefully acknowledged. N.G.B. acknowledges financial support by MINECO through the Ramon y Cajal program (RYC-2012-10991). ICN2 is supported by the Severo Ochoa program from Spanish MINECO (grant no. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya. Part of the present work has been performed in the framework of the Universitat Autonoma de Barcelona Degree and Ph.D. program.

Here, we report the synthesis of (multi)-layered zeolitic imidazolate framework (ZIF-8/-67) composite particles via a sequential deconstruction–reconstruction process. We show that this process can be applied to construct ZIF-8-on-ZIF-67 composite particles whose cores are the initially etched particles. In addition, we demonstrate that introduction of functional inorganic nanoparticles (INPs) onto the crystal surface of etched particles does not disrupt ZIF particle reconstruction, opening new avenues for designing (multi)-layered ZIF-on-INP-on-ZIF composite particles comprising more than one class of inorganic nanoparticles. In these latter composites, the location of the inorganic nanoparticles inside each single metal–organic framework particle as well as of their separation at the nanoscale (20 nm) is controlled. Preliminary results show that (multi)-layered ZIF-on-INP-on-ZIF composite particles comprising a good sequence of inorganic nanoparticles can potentially catalyze cascade reactions., This work was supported by the EU FP7 ERC-Co 615954, the Spanish MINECO (projects PN MAT2015-65354-C2-1-R, MAT2015-70725-R, and CTQ2016-77989-P), and the Catalan AGAUR (projects 2014 SGR 80, 2014 SGR 612 and 2014 SGR 862). It was also funded by the CERCA Program/Generalitat de Catalunya. N.G.B. acknowledges financial support by MINECO through the Ramon y Cajal program (RYC-2012-10991). ICN2 acknowledges the support of the Spanish MINECO through the Severo Ochoa Centers of Excellence Program under Grant SEV-2013-0295.

We re-evaluate the evidence presented for the detection of mRNA in cells and tissues with Spherical Nucleic Acids.

Au-coated magnetic-core nanocomposites with diameters of ∼100 nm were synthesized by the biphasic reduction of Au3+ onto the surface of organosilane-stabilized Co nanoparticles of ∼12 nm in diameter via an iterative gold reduction. The shell consists initially of Au seeds of ∼3 nm in diameter, which can be later grown to form partially fused ∼6 nm Au NPs. A detailed investigation by transmission electron microscopy, scanning electron microscopy, UV–vis, dynamic light scattering, ζ-potential, X-ray diffraction, inductively coupled plasma mass spectrometry, and superconducting quantum interference device magnetometry was performed in order to elucidate the morphology and properties of these nanocomposites. These novel nanoarchitectures, which could be transferred into aqueous phase by means of an amphiphilic polymer, showed low cytotoxicity on human HepG2 cells and presented relaxivity in MRI contrast enhancement experiments.

The present work faces the rising demand of cationic particles of different sizes for biological applications, especially in gene therapies and nanotoxicology studies. A simple phase-transfer methodology has been developed for the functionalization of gold nanoparticles (Au NPs) with a variety of ligands, both cationic and anionic in aqueous solution, employing different nanocrystal sizes with narrow size distributions. Successful functionalization has been demonstrated by UV-vis spectroscopy, DLS, ζ-potential, and FTIR spectroscopy characterization of the particles before and after the phase transfer. The intracellular uptake of the differently charged Au NPs functionalized with peptidic biomolecules was investigated with human fibroblasts (1BR3G) by ICP-MS analysis of the digested cells and confocal fluorescence microscopy, which showed increased internalization of the cationic bioconjugates. Nuclear targeting could be observed by TEM, suggesting that the cationic peptidic biomolecule is acting as a nuclear localization signal.

The role of sodium citrate (SC) in the formation and growing mechanism of gold nanoparticles was systematically examined. Obtained results show that oxidation of SC can be induced either by the presence of HAuCl4 or by its thermal decomposition under air. By exchanging the order of reagent addition, it is possible to increase the oxidation rate of SC and hence control the size and morphology, thus allowing preparation of nanoparticles with a narrower size distribution than the standard Turkevich approach.

Nearly monodisperse iron oxide colloidal nanocrystals prepared by nonhydrolytic high-temperature solution method were obtained with two different sizes and degrees of oxidation. The characterization of the structural features of the nanocrystals was performed by a multitechnique approach including transmission electron microscopy, X-ray diffraction and X-ray absorption spectroscopy, energy filtered electron microscopy imaging, and SQUID magnetometry. The different techniques provided complementary information on the local oxidation state of iron in the iron oxide nanoparticles, the stability of the phases, the exact crystal structure, and the compositional homogeneity. X-ray diffraction, transmission electron microscopy, and extended X-ray absorption spectroscopy show that the addition of oxidizer to the iron precursor gives rise to monodisperse polycrystalline nanoparticles made out of FeO plus a spinel phase. X-ray absorption near-edge structure, which is very sensitive to the oxidation state and local ...

Gold nanoparticles of 6, 8, and 16 nm, synthesized with HAuCl(4) and sodium citrate, were derived with biomolecules based on the peptide CIPGNVG and possessing different terminal charges. We have studied the stability of these conjugates as a function of ionic strength, pH, and the presence of other species in solution. It was observed that multiple electrostatic interactions between the conjugates mediated by cross-linking species led to an effective strong bond and consequently to irreversible aggregation and precipitation. In the presence of citrate or diamine ions, nanoparticles precipitated when two-headed ions had charges opposite (and therefore attractive) to the conjugate, thus acting as bridging molecules. This effect depends on the pH, the concentration of particles, and their size, and it is relevant to designing bioconjugates for biomedical applications.

A low-temperature route to pure CoO nanoparticles based on the oxidative decarbonylation of dicobalt octacarbonyl promoted by amine oxides is presented. The small size of the resulting particles (∼1.7 nm) leads to spontaneous nanoparticle aggregation. Magnetic measurements show a bimodal behavior with two distinct blocking temperatures, which can be ascribed to the individual CoO nanoparticles and to narrowly size-dispersed aggregates.

Subnanometric cobalt metallic particles, with an average size of 0.8 nm and an estimated number of 50 atoms, have been stabilized in the confined spaces within the nanopores of crystalline molecular sieves. Remarkably, these clusters show a rapid vanishing of the magnetization as the temperature is increased from 10 to 20 K because of the ferromagnetic-paramagnetic transition together with thermal fluctuations of the remaining moment. This dramatic reduction of the transition temperature is due to strong finite size effects. Such behavior, predicted for very small metallic particles, was never observed before due to the inherent difficulty in achieving subnanometric stable metallic particles.

Mesoporous silica was synthesized in the presence of metal (Au, Pt, and Ag) nanoparticles in the 2−20 nm range. Sample characterization was performed by X-ray diffraction and electron microscopy. The metal nanoparticles in the 2−10 nm range were successfully incorporated into the ordered mesoporous SBA-15 structures; 20 nm particles, whose diameter is larger than the SBA-15 pore size, could not be inserted. In the case of 5 and 10 nm diameter nanoparticles, regardless of which metal, the mesopore channels expanded in order to accommodate the metal particles. By using mixtures of metal nanoparticles of two different sizes, it was found that the inclusion and the resultant pore size were controlled by the larger size metal particles.

Industrial catalysts often consist of transition metals supported on microporous or mesoporous high surface area oxides and are prepared by techniques such as impregnation and ion adsorption. In standard fabrication processes the metal particle size is not well-controlled. In this paper we report a new synthetic route for the production of catalyst materials with more precise control of the metal particle size. Gold nanoparticles encapsulated in mesoporous silica (MCM-41 and MCM-48) served as a model system, although the techniques described are applicable to a wide variety of metals and oxide supports. The samples were characterized by a combination of low-angle powder X-ray diffraction, transmission electron microscopy, N2 porosimetry, infrared spectroscopy, and X-ray absorption near-edge spectroscopy. The results show that the MCM-41 and MCM-48 structures retain their long-range order when metal particles are added; in addition, the size of the channels increases monotonically with metal loading. X-ray...

hcp Co disk-shaped nanocrystals were obtained by rapid decomposition of cobalt carbonyl in the presence of linear amines. Other surfactants, in addition to the amines, like phosphine oxides and oleic acid were used to improve size dispersion, shape control, and nanocrystal stability. Co disks are ferromagnetic in character and they spontaneously self-assemble into long ribbons. X-ray and electron diffraction, electron microscopy, and SQUID magnetometry have been employed to characterize this material.

Metallic nanoparticles (platinum and gold) encapsulated in mesoporous silica (SBA-15) were prepared in the same solution by a novel two-step method. Characterization by X-ray scattering and electron microscopy consistently shows that the metal nanoparticles were homogeneously incorporated in the mesopores (retaining their size and morphology), even when the nanocrystal diameter exceeds the normal mesopore diameter. The nanoparticles nucleated the expansion of the mesopore channels in the 92−116 A range so they could accommodate the metal particles. This expansion occurs in the concentration range of 1−103 nanoparticles per 103 mesopore channels. This effect can be used to tune the pore size.

In the present work, we analyze the geometry and composition of the nanostructures obtained from the oxidation of iron nanoparticles. The initial oxidation of iron takes place by outward diffusion of cations through the growing oxide shell. This net material flow is balanced by an opposite flow of vacancies, which coalesce at the metal/oxide interface. Thus, the partial oxidation of colloidal iron nanoparticles leads to the formation of core−void−shell nanostructures. Furthermore, the complete oxidation of iron nanoparticles in the 3−8 nm size range leads to the formation of hollow iron oxide nanoparticles. We analyze the size and temperature range in which vacancy coalescence during oxidation of amine-stabilized iron nanoparticles takes place. Maghemite is the crystallographic structure obtained from the complete oxidation of iron nanoparticles under our synthetic conditions.

10 páginas, 10 figuras, 1 tabla, 1 esquema., The introduction of metallic traces into the synthesis of platinum nanocrystals (Pt NCs) has been investigated as a surfactant-independent means of controlling shape. Various nanocrystal morphologies have been produced without modification of the reaction conditions, composition, and concentration other than the presence of cobalt traces (, The work is supported by the Spanish MICIN. S.L. acknowledges the support from a Beatriu de Pinós fellowship from the Catalan Government.