Search

Lead halide perovskite nanocrystals (LHP NCs) have emerged as next-generation semiconductor materials with outstanding optical and optoelectronic properties. Because of the high surface-to-volume ratio, the optical and optoelectronic performance and the colloidal stability of LHP NCs largely depend on their surface chemistry, especially the ligands and surface termination. On one hand, the capping ligands improve the colloidal stability and luminescence; on the other hand the highly dynamic binding nature of ligands is detrimental to the colloidal stability and photoluminescence of LHP NCs. In addition, the surface functionalization with desired molecules induces new functionalities such as chirality, light harvesting, and triplet sensitization through energy/electron transfer or use as X-ray detectors. In this review, we present the current understanding of an atomic view of the surface chemistry of colloidal LHP NCs, including crystal termination, vacancies, and different types of capping ligands. Furthermore, we discuss the ligand-induced functionalities, including photocatalysis and chirality. Deutsche Forschungsgemeinschaft | Ref. EXC 2089/1 390776260 Xunta de Galicia | Ref. ED431F2021/05 Agencia Estatal de Investigación | Ref. RYC2018-026103-I Agencia Estatal de Investigación | Ref. PID2020-117371RA-I00 Universidade de Vigo/CISUG

A robust and reproducible methodology to prepare stable inorganic nanoparticles with chiral morphology may hold the key to the practical utilization of these materials. An optimized chiral growth method to prepare fourfold twisted gold nanorods is described herein, where the amino acid cysteine is used as a dissymmetry inducer. Four tilted ridges are found to develop on the surface of single-crystal nanorods upon repeated reduction of HAuCl4, in the presence of cysteine as the chiral inducer and ascorbic acid as a reducing agent. From detailed electron microscopy analysis of the crystallographic structures, it is proposed that the dissymmetry results from the development of chiral facets in the form of protrusions (tilted ridges) on the initial nanorods, eventually leading to a twisted shape. The role of cysteine is attributed to assisting enantioselective facet evolution, which is supported by density functional theory simulations of the surface energies, modified upon adsorption of the chiral molecule. The development of R-type and S-type chiral structures (small facets, terraces, or kinks) would thus be non-equal, removing the mirror symmetry of the Au NR and in turn resulting in a markedly chiral morphology with high plasmonic optical activity.

The development of plasmonic nanomaterials with chiral geometry has drawn extensive attention owing to their practical implications in chiral catalysis, chiral metamaterials, or enantioselective biosensing and medicine. However, due to the lack of effective synthesis methods of hydrophobic nanoparticles (NPs) showing intrinsic, plasmonic chirality, their applications are currently limited to aqueous systems. In this work, we resolve the problem of achieving hydrophobic Au NPs with intrinsic chirality by efficient phase transfer of water-soluble NPs using low molecular weight, liquid crystal-like ligands. We confirmed that, after the phase transfer, Au NPs preserve strong, far-field circular dichroism (CD) signals, attesting their chiral geometry. The universality of the method is exemplified by using different types of NPs and ligands. We further highlight the potential of the proposed approach to realize chiral plasmonic, inorganic/organic nanocomposites with block copolymers, liquid crystals, and compounds forming physical gels. All soft matter composites sustain plasmonic CD signals with electron microscopies confirming well-dispersed nanoinclusions. The developed methodology allows us to expand the portfolio of plasmonic NPs with intrinsic structural chirality, thereby broadening the scope of their applications toward soft-matter based systems., W.L., N.K., F.B., J.K., and M.B. acknowledge support from the National Science Center Poland under the OPUS grant number UMO-2019/35/B/ST5/04488. I.P.-S., J.P.-J., and S.G.-G. acknowledge support from MCIN/AEI/10.13039/501100011033 (grants PID2019-108954RB-I00 and PID2020-117371RA-I00) and Xunta de Galicia/FEDER (grant GRC ED431C2020/09). M.G. acknowledges support from MCIN/AEI/10.13039/501100011033 (grant PID2019-111772RB-I00).

International audience; Organizing nanoparticles (NPs) into periodic structures is a central goal in materials science. Despite progress in the last decades, it is still challenging to produce macroscopic assemblies reliably. In this work, we report the analysis of the pervaporation-induced organization of gold octahedra into supercrystals within microfluidic channels using a combination of X-ray scattering techniques and FIB-SEM tomography. The results reveal the formation of a singledomain supercrystal with a monoclinic C2/m symmetry and long-range order extending over the dimensions of the microfluidic channel, covering at least 1.7x0.3 mm 2. Time-resolved small angle X-ray scattering analysis showed that the formation of the superlattice involves an accumulation of the NPs within the channel before the nucleation and growth of the supercrystal. The orientation of the crystal remains unchanged during its formation, suggesting a growth mechanism directed by the channel interface. Together, these results show the potential application of the pervaporation strategy to providing spatially determined control over NP crystallization, which can be used for the rational fabrication of nanomaterial architectures.

Tuberculosis remains today a major public health issue with a total of 9 million new cases and 2 million deaths annually. The lack of an effective vaccine and the increasing emergence of new strains of Mycobacterium tuberculosis (Mtb) highly resistant to antibiotics, anticipate a complicated scenario in the near future. The use of nanoparticles features as an alternative to antibiotics in tackling this problem due to their potential effectiveness in resistant bacterial strains. In this context, silver nanoparticles have demonstrated high bactericidal efficacy, although their use is limited by their relatively high toxicity, which calls for the design of nanocarriers that allow silver based nanoparticles to be safely delivered to the target cells or tissues. In this work mesoporous silica nanoparticles are used as carriers of silver based nanoparticles as antimycobacterial agent against Mtb. Two different synthetic approaches have been used to afford, on the one hand, a 2D hexagonal mesoporous silica nanosystem which contains silver bromide nanoparticles distributed all through the silica network and, on the other hand, a core@shell nanosystem with metallic silver nanoparticles as core and mesoporous silica shell in a radial mesoporous rearrangement. Both materials have demonstrated good antimycobacterial capacity in in vitro test using Mtb, being lower the minimum inhibitory concentration for the nanosystem which contains silver bromide. Therefore, the interaction of this material with the mycobacterial cell has been studied by cryo-electron microscopy, establishing a direct connection between the antimycobactericidal effect observed and the damage induced in the cell envelope., 28 pages, 6 figures

The poor delivery of nanoparticles to target cancer cells hinders their success in the clinical setting. In this work, an alternative target readily available for circulating nanoparticles has been selected to eliminate the need for nanoparticle penetration in the tissue: the tumor blood vessels. A tumor endothelium-targeted nanoparticle (employing an RGD-containing peptide) capable of co-delivering two anti-vascular drugs (one anti-angiogenic drug and one vascular disruption agent) is here presented. Furthermore, the nanodevice presents two additional anti-vascular capabilities upon activation by Near-Infrared light: provoking local hyperthermia (by gold nanorods in the system) and generating toxic reactive oxygen species (by the presence of a photosensitizer). RGD-targeting is shown to increase uptake by HUVEC cells, and while the nanoparticles are shown not to be toxic for these cells, upon Near-Infrared irradiation their almost complete killing is achieved. The combination of all four therapeutic modalities is then evaluated in an ex ovo fibrosarcoma xenograft model, which shows a significant reduction in the number of blood vessels irrigating the xenografts when the nanoparticles are present, as well as the destruction of the existing blood vessels upon irradiation. These results suggest that the combination of different anti-vascular therapeutic strategies in a single nanocarrier appears promising and should be further explored in the future., 33 pages, 8 figures

Surface-enhanced Raman spectroscopy (SERS) microfluidic chips for label-free and ultrasensitive detection are fabricated by integrating a plasmonic supercrystal within microfluidic channels. This plasmonic platform allows the uniform infiltration of the analytes within the supercrystal, reaching the so-called hot spots. Moreover, state-of-the-art simulations performed using large-scale supercrystal models demonstrate that the excellent SERS response is due to the hierarchical nanoparticle organization, the interparticle separation (IPS), and the presence of supercrystal defects. Proof-of-concept experiments confirm the outstanding performance of the microfluidic chips for the ultradetection of (bio)molecules with no metal affinity. In fact, a limit of detection (LOD) as low as 10-19 M was reached for crystal violet. The SERS microfluidic chips show excellent sensitivity in the direct analysis of pyocyanin secreted by Pseudomonas aeruginosa grown in a liquid culture medium. Finally, the further integration of a silica-based column in the plasmonic microchip provides charge-selective SERS capabilities as demonstrated for a mixture of positively and negatively charged molecules.

For decades, plasmonic nanoparticles have been extensively studied due to their extraordinary properties, related to localized surface plasmon resonances. A milestone in the field has been the development of the so-called seed-mediated growth method, a synthetic route that provided access to an extraordinary diversity of metal nanoparticles with tailored size, geometry and composition. Such a morphological control came along with an exquisite definition of the optical response of plasmonic nanoparticles, thereby increasing their prospects for implementation in various fields. The susceptibility of surface plasmons to respond to small changes in the surrounding medium or to perturb (enhance/quench) optical processes in nearby molecules, has been exploited for a wide range of applications, from biomedicine to energy harvesting. However, the possibilities offered by plasmonic nanoparticles can be expanded even further by their careful assembly into either disordered or ordered structures, in 2D and 3D. The assembly of plasmonic nanoparticles gives rise to coupling/hybridization effects, which are strongly dependent on interparticle spacing and orientation, generating extremely high electric fields (hot spots), confined at interparticle gaps. Thus, the use of plasmonic nanoparticle assemblies as optical sensors have led to improving the limits of detection for a wide variety of (bio)molecules and ions. Importantly, in the case of highly ordered plasmonic arrays, other novel and unique optical effects can be generated. Indeed, new functional materials have been developed via the assembly of nanoparticles into highly ordered architectures, ranging from thin films (2D) to colloidal crystals or supercrystals (3D). The progress in the design and fabrication of 3D supercrystals could pave the way toward next generation plasmonic sensors, photocatalysts, optomagnetic components, metamaterials, etc. In this Account, we summarize selected recent advancements in the field of highly ordered 3D plasmonic superlattices. We first analyze their fascinating optical properties for various systems with increasing degrees of complexity, from an individual metal nanoparticle through particle clusters with low coordination numbers to disordered self-assembled structures and finally to supercrystals. We then describe recent progress in the fabrication of 3D plasmonic supercrystals, focusing on specific strategies but without delving into the forces governing the self-assembly process. In the last section, we provide an overview of the potential applications of plasmonic supercrystals, with a particular emphasis on those related to surface-enhanced Raman scattering (SERS) sensing, followed by a brief highlight of the main conclusions and remaining challenges.

In this review, we summarize the recent research focused on the combination of inorganic nanoparticles and α-, β- and γ- cyclodextrins. Our intention is to highlight the most relevant publications on the synthesis of nanoparticle-cyclodextrin (NP-CD) nanohybrids, with CDs acting as reducing agents or through the post-synthetic modification of inorganic nanoparticles with CDs. We also discuss the new or enhanced properties that arise from the host-guest capabilities of the CDs and inorganic nanoparticles. Finally, we illustrate the potential applications of these materials in numerous research fields.

Melanoma is one of the most severe public health issues worldwide, not only because of the high number of cases but also for its poor prognosis in late stages. Therefore, early diagnosis and efficient treatment are key toward a future solution. However, melanoma is highly resistant to cytotoxicity in its metastatic form. In this context, a therapeutic strategy based on a targeted chemo‐photothermal nanotransporter for cytotoxic compounds is proposed. This approach comprises the use of core–multishell gold nanorods, coated with mesoporous silica and further covered with a thermosensitive polymer, which is vectorized for selective internalization in melanoma cells. The proposed nanoformulation is capable of releasing the transported cytotoxic compounds on demand, in response to near‐IR irradiation, with high selectivity and efficacy against malignant cells, even at low concentrations, thereby providing a new tool against melanoma disease.

Amphiphilic nonionic ligands, synthesized with a fixed hydrophobic moiety formed by a thiolated alkyl chain and an aromatic ring, and with a hydrophilic tail composed of a variable number of oxyethylene units, were used to functionalize spherical gold nanoparticles (AuNPs) in water. Steady-state and time-resolved fluorescence measurements of the AuNPs in the presence of α-cyclodextrin (α-CD) revealed the formation of supramolecular complexes between the ligand and macrocycle at the surface of the nanocrystals. The addition of α-CD induced the formation of inclusion complexes with a high apparent binding constant that decreased with the increasing oxyethylene chain length. The formation of polyrotaxanes at the surface of AuNPs, in which many α-CDs are trapped as hosts on the long and linear ligands, was demonstrated by the formation of large and homogeneous arrays of self-assembled AuNPs with hexagonal close packing, where the interparticle distance increased with the length of the oxyethylene chain. The estimated number of α-CDs per polyrotaxane suggests a high rigidization of the ligand upon complexation, allowing for nearly perfect control of the interparticle distance in the arrays. This degree of supramolecular control was extended to arrays formed by AuNPs stabilized with polyethylene glycol and even to binary arrays. Electromagnetic simulations showed that the enhancement and distribution of the electric field can be finely controlled in these plasmonic arrays., This work was funded by the Spanish MINECO (MAT2014-59678-R and CTQ2015-65972-R), and the Madrid Regional Government (S2013/MIT-2807). A.G.-M. and S.G.-G. acknowledge receipt of a “Ramón y Cajal” and “Juan de la Cierva” fellowships, respectively, from the Spanish MINECO. P.D.N. acknowledges DIMMAT project funded by the Madrid Regional Government (S2013/MIT-2775). The authors acknowledge the facilities provided by the Nuclear Magnetic Resonance Center and the National Center of Microscopy (Universidad Complutense de Madrid).

Raspberry-like magnetic nanoclusters are synthesized and subsequently self-assembled to form a bulk metamaterial exhibiting strong isotropic optical magnetism in visible light. The magnetic response of the nanoclusters (metamolecules) and of the final assembled material are measured by independent optical experiments. The validity of the effective permeability parameter is probed by spectroscopic ellipsometry at variable incidence. Numerical simulations confirm the measurements.

Shape-controlled synthesis of uniform noble metal nanoparticles (NPs) is crucial for the development of future plasmonic devices. The use of nanocrystals with well-defined morphologies and crystallinity as seed particles is expected to provide excellent shape control and monodispersity. We report the aqueous-based seed-mediated growth of monodisperse gold octahedra with wide range of sizes (50–150 nm in side length) by reducing different amounts of HAuCl4 on preformed single crystalline gold nanorods using butenoic acid as reducing agent. Butenoic acid plays a key role as a mild reducing agent as well as favoring the thermodynamic control of the reaction. The uniformity of the as-prepared Au octahedra combined with the use of a microfluidic technique based on microevaporation will allow the self-assembly of octahedra into uniform 3D supercrystals. Additionally, these plasmonic substrates exhibit high and uniform SERS signals over extended areas with intensities increasing with the Au nanoparticle size.

The implementation of nanoparticles as nanomedicines require from sophisticated surface modifications in order to reduce immune response and enhance recognition abilities. In addition to that, Mesoporous Silica nanoparticles present extraordinary host-guest abilities and facile surface functionalization. These two factors make them ideal candidates for the development of novel drug delivery systems, at the expense of increasing the structural complexity. With this idea in mind, a system of triggerable and tunable silica nanoparticles was developed for its application as drug delivery nanocarriers. For that purpose, Diels-Alder cycloaddition adducts were chosen as thermalresponsive units; that permitted to bind Au nanocaps able to block the pores and allow the incorporation of targeting fragments. The capping efficiency was tested under different thermal conditions, obtaining outstanding efficiencies within the physiological range and mild temperatures, as well as enhanced releases under pulsing heating cycles which showed the best release profiles.

Seed-mediated growth is the most efficient methodology to control the size and shape of colloidal metal nanoparticles. In this process, the final nanocrystal shape is defined by the crystalline structure of the initial seed as well as by the presence of ligands and other additives that help to stabilize certain crystallographic facets. We analyze here the growth mechanism in aqueous solution of silver shells on presynthesized gold nanoparticles displaying various well-defined crystalline structures and morphologies. A thorough three-dimensional electron microscopy characterization of the morphology and internal structure of the resulting core-shell nanocrystals indicates that {100} facets are preferred for the outer silver shell, regardless of the morphology and crystallinity of the gold cores. These results are in agreement with theoretical analysis based on the relative surface energies of the exposed facets in the presence of halide ions.

11] and encouraged by the need of optimization of the self-assembly process that may allow the design of large-scale supercrystals with high optical activity for SERS detection, we report on a straightforward approach to obtain long-range plas-monic supercrystals made of standing core-shell gold-silver nanorods (Au@AgNRs), stabilized with gemini surfactants, by controlling the drop casting conditions. Au@AgNRs (length = 71

International audience; Raspberry-like nano-objects made of large plasmonic satellites (>10 nm) covering a central dielectric particle have many potential applications as photonic materials, superlenses and (bio-) sensors, but their synthesis remains challenging. Herein, we show how to build stable and robust raspberry-like nano-systems with close-packed satellites, by combining monodisperse silica particles (80 or 100 nm diameter) and oppositely charged noble metal nanoparticles (Au or Ag) with well-defined sizes (10-50 nm). The spectral characteristics of their associated plasmonic resonances (wavelength, linewidth, extinction cross-section) and the electromagnetic coupling between satellites were observed using the spatial modulation spectroscopy technique and interpreted through a numerical model. The composite nano-objects exhibit numerous hot spots at satellite junctions, resulting in excellent surface-enhanced Raman scattering (SERS) performance. The SERS efficiency of the raspberry-like clusters is highly dependent on their structure.

Twisting nanoparticles: Plasmonic circular dichroism was experimentally obtained in chiral 3D organizations of gold nanorods obtained by self-assembly of the nanoantennas onto a fiber template with a twisted morphology. Numerical simulations based on coupled dipoles confirm the crucial role of gold nanorods in this intense circular dichroism

International audience; Modification of the plasmonic response of a metal nano-object due to interaction with a substrate is experimentally investigated measuring the quantitative optical extinction spectra of individual nano-objects with various elongated shapes (bipyramids and rods) deposited on a dielectric (silica) or absorbing (carbon) membrane. Apart from the expected dependence of the nanoparticle surface plasmon resonance (SPR) frequency on the nature of the substrate, large substrate and particle shape dependent modifications of its SPR width are demonstrated. These dependencies are ascribed to strong localization of the electromagnetic field associated with the longitudinal SPR of an elongated nano-object around its tips, leading to different interaction with the substrate depending on the particle shape and 3D orientation relative to the substrate. Both parameters have been precisely determined by electron tomography, permitting excellent reproduction of the experimental data. Experiments performed on silver-encapsulated bipyramids, whose shape evolves from a pyramidal one towards a cylindrical one, further confirm this effect.

International audience; We present a full experimental characterization of isotropic artificial optical magnetism at visible frequencies produced by “raspberrylike” plasmonic nanoclusters synthesized by a bottom-up approach. Experimental measurements of extinction and light scattering associated with numerical simulations enable one to extract absolute values of the magnetic scattering cross section across the whole visible spectral range. The strength of the resonant magnetic response of a single magnetic nanocluster is illustrated as the effective magnetic permeability of a homogeneous sphere of identical volume.

A thorough understanding of the three-dimensional (3D) atomic structure and composition of coreshell nanostructures is indispensable to obtain a deeper insight on their physical behavior. Such 3D information can be reconstructed from two-dimensional (2D) projection images using electron tomography. Recently, different electron tomography techniques have enabled the 3D characterization of a variety of nanostructures down to the atomic level. However, these methods have all focused on the investigation of nanomaterials containing only one type of chemical element. Here, we combine statistical parameter estimation theory with compressive sensing based tomography to determine the positions and atom type of each atom in heteronanostructures. The approach is applied here to investigate the interface in coreshell Au@Ag nanorods but it is of great interest in the investigation of a broad range of nanostructures.

It is widely accepted that the physical properties of nanostructures depend on the type of surface facets1, 2. For Au nanorods, the surface facets have a major influence on crucial effects such as reactivity and ligand adsorption and there has been controversy regarding facet indexing3, 4. Aberration-corrected electron microscopy is the ideal technique to study the atomic structure of nanomaterials5, 6. However, these images correspond to two-dimensional (2D) projections of 3D nano-objects, leading to an incomplete characterization. Recently, much progress was achieved in the field of atomic-resolution electron tomography, but it is still far from being a routinely used technique. Here we propose a methodology to measure the 3D atomic structure of free-standing nanoparticles, which we apply to characterize the surface facets of Au nanorods. This methodology is applicable to a broad range of nanocrystals, leading to unique insights concerning the connection between the structure and properties of nanostructures.

Gold nanorods in aqueous solution are generally surrounded by surfactants or capping agents. This is crucial for anisotropic growth during synthesis and for their final stability in solution. When CTAB is used, a bilayer has been evidenced from analytical methods even though no direct morphological characterization of the precise thickness and compactness has been reported. The type of surfactant layer is also relevant to understand the marked difference in further self-assembling properties of gold nanorods as experienced using 16-EO(1)-16 gemini surfactant instead of CTAB. To obtain a direct measure of the thickness of the surfactant layer on gold nanorods synthesized by the seeded growth method, we coupled TEM, SAXS, and SANS experiments for the two different cases, CTAB and gemini 16-EO(1)-16. Despite the strong residual signal from micelles in excess, it can be concluded that the thickness is imposed by the chain length of the surfactant and corresponds to a bilayer with partial interdigitation.