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The localized surface plasmon resonance (LSPR) of gold nanospheres dispersed in methanol–ethanol 4:1 was measured as a function of pressure up to 60 GPa. The LSPR exhibits an intense red-shift with...

We present a study that allows us to explain the chemical changes behind the often observed but so far ununderstood drift of the plasmon resonance of chemically prepared gold nanorods in microfluid...

International audience; The density and compressibility of nanoscale gold (both nanospheres and nanorods) and microscale gold (bulk) were simultaneously studied by X-ray diffraction with synchrotron radiation up to 30 GPa. Colloidal stability (aggregation state and nanoparticle shape and size) in both hydrostatic and nonhydrostatic regions was monitored by small-angle X-ray scattering. We demonstrate that nonhydrostatic effects due to solvent solidification had a negligible influence on the stability of the nanoparticles. Conversely, nonhydrostatic effects produced axial stresses on the nanoparticle up to a factor 10× higher than those on the bulk metal. Working under hydrostatic conditions (liquid solution), we determined the equation of state of individual nanoparticles. From the values of the lattice parameter and bulk modulus, we found that gold nanoparticles are slightly denser (0.3%) and stiffer (2%) than bulk gold: V 0 = 67.65(3) Å 3 , K 0 = 170(3)GPa, at zero pressure.

The interaction of several components in the strong coupling regime yielding multiple Rabi splittings opens up remarkable possibilities for studies of multimode hybridization and energy transfer, which is of considerable interest in both fundamental and applied science. Here we demonstrate that three different components, such as core−shell Au@Ag nanorods and J-aggregates of two different dyes, can be integrated into a single hybrid structure, which leads to strong collective exciton− plasmon coupling and double-mode Rabi splitting totaling 338 meV. We demonstrate strong coupling in these multicomponent plexitonic nanostructures by means of magnetic circular dichroism spectroscopy and demonstrate strong magneto-optical activity for the three hybridized states resulting from this coupling. The J-aggregates of two different nonmagnetic dyes interact with metal nanoparticles effectively, achieving magnetic properties due to the hybridization of electronic excitations in the threecomponent system., This work was supported by MINECO (Ministerio de Economiá y Competitividad), Spain, Projects FIS2016-80174-P (PLASMOQUANTA) and MAT2017-86659-R (MULTIMAGE). I.R.N. and Y.P.R. acknowledge support from the Ministry of Education and Science of the Russian Federation under Grant No. 14.Y26.31.0011 and funding from the Basque Government (Grant No. IT1164-19). This work was coordinated under the Maria de Maeztu Units of Excellence Program from the Spanish State Research Agency (Grant No. MDM-2017-0720).

This work was partially supported by the European Research Council ERC-CoG-648071-ProNANO, ERC-PoC-841063-NIMM, Agencia Estatal de Investigación, Spain (PID2019- 111649RB-I00; and MAT2017-88693-R), and the Basque Government (Elkartek KK-2017/00008), E.L-M thanks the Spanish Ministry of Science and Innovation for the FPI grant (BES-2017-079646). This work was performed under the Maria de Maeztu Units of Excellence Program from the Spanish State Research Agency – Grant No. MDM-2017-0720 (CIC biomaGUNE) and SEV-2016-0686 (IMDEA Nanociencia)., Protein-based materials are usually considered as insulators, although conductivity has been recently shown in proteins. This fact opens the door to develop new biocompatible conductive materials. While there are emerging efforts in this area, there is an open challenge related to the limited conductivity of protein-based systems. This work shows a novel approach to tune the charge transport properties of protein-based materials by using electron-dense AuNPs. Two strategies are combined in a unique way to generate the conductive solid films: (1) the controlled self-assembly of a protein building block; (2) the templating of AuNPs by the engineered building block. This bottom-up approach allows controlling the structure of the films and the distribution of the AuNPs within, leading to enhanced conductivity. This work illustrates a promising strategy for the development of effective hybrid protein-based bioelectrical materials., European Research Council (ERC) European Commission ERC-CoG-648071-ProNANO ERC-PoC-841063-NIMM, Agencia Estatal de Investigacion, Spain PID2019111649RB-I00 MAT2017-88693-R, Basque Government Elkartek KK-2017/00008, Spanish Government BES-2017-079646, Maria de Maeztu Units of Excellence Program from the Spanish State Research Agency MDM-2017-0720 SEV-2016-0686

Excitons in semiconductor quantum dots (QDs) feature high values of the two-photon absorption cross-sections (TPACSs), enabling applications of two-photon-excited photoluminescence (TPE PL) of QDs in biosensing and nonlinear optoelectronics. However, efficient TPE PL of QDs requires high-intensity laser fields, which limits these applications. There are two possible ways to increase the TPE PL of QDs: by increasing their photoluminescence quantum yield (PLQY) or by further increasing the TPACS. Plasmonic nanoparticles (PNPs) may act as open nanocavities for increasing the PLQY via the Purcell effect, but this enhancement is strictly limited by the maximum possible PLQY value of 100%. Here we directly investigated the effect of PNPs on the effective TPACS of excitons in QDs. We have found that effective TPACS of excitons in a QD–PMMA thin film can be increased by a factor of up to 12 near the linearly excited gold nanorods (GNRs). Using gold nanospheres (GNSs), in which plasmons cannot be excited in the infrared range, as a control system, we have shown that, although both GNSs and GNRs increase the recombination rate of excitons, the TPACS is increased only in the case of GNRs. We believe that the observed effect of TPACS enhancement is a result of the nonlinear interaction of the plasmons in GNRs with excitons in QDs, which we have supported by numerical simulations. The results show the way to the rational design of the spectral features of plasmon–exciton hybrids for using them in biosensing and nonlinear optoelectronics., V. K. acknowledges support from the Russian Science Foundation (Grant No. 18-72-10143) for the part of the study related to the investigation of the effects of PNPs on the effective TPACS of excitons in QDs and numerical simulations of these effects. Support from the Ministry of Education and Science of the Russian Federation (Grant No. 14.Y26.31.0011) for the part of this study related to the synthesis and functionalisation of the QDs and engineering of hybrid QD-GNR materials is also acknowledged. Y. R. acknowledges the support from the Basque Government (grant no. IT1164-19). Y. R. and M. G. acknowledge the support from the Spanish MINECO (PID2019-111772RB-I00). I. N. acknowledges the Ministry of Higher Education, Research and Innovation of the French Republic and Université de Reims Champagne-Ardenne.

The detection of cancer biomarkers at an early stage of tumor development is vital for effective diagnosis and treatment of cancer. Current diagnostic tools can often detect cancer only when the biomarker levels are already too high, so that the tumors have spread and treatments are less effective. It is urgent therefore to develop highly sensitive assays for the detection of such biomarkers at the lowest possible concentration. In this context, we developed a sandwich immunoassay based on surface-enhanced Raman scattering (SERS) for the ultrasensitive detection of alpha-fetoprotein (AFP), which is typically present in human serum as a biomarker indicative of early stages of hepatocellular carcinoma. In the immunoassay design, molybdenum disulfide (MoS2) modified with a monoclonal antibody was used as a capture probe for AFP. A secondary antibody linked to an SERS-encoded nanoparticle was employed as the Raman signal reporter, that is, the transducer for AFP detection. The sandwich immunocomplex "capture probe/target/SERS tag" was deposited on a silicon wafer and decorated with silver-coated gold nanocubes to increase the density of "hot spots" on the surface of the immunosensor. The developed SERS immunosensor exhibits a wide linear detection range (1 pg mL(-1) to 10 ng mL(-1)) with a limit of detection as low as 0.03 pg mL(-1) toward AFP with good reproducibility (RSD < 6%) and stability. These parameters demonstrate that the proposed immunosensor has the potential to be used as an analytical platform for the detection of early-stage cancer biomarkers in clinical applications E.E. is grateful for a fellowship from the Scientific and Technological Research Council of Turkey (TUBITAK). A.C. and A.S. thank MINECO for their research grant (Juan de la Cierva.Incorporacion/no. IJCI-2016-31113, Juan de la Cierva. Formacion/no. FJC2018-036777-I, respectively). We thank Dr. Judith Langer for support in the interpretation of SERS results. This work was supported by the European Union's Horizon 2020 research and innovation program under Grant Agreements 785219 and 881603 Graphene Flagship. L.M.L.-M. acknowledges funding from the European Research Council (ERC-AdG-2017#787510). M.P., as the recipient of the AXA Bionanotechnology Chair, is grateful to the AXA Research Fund for financial support. This work was performed under the Maria de Maeztu Units of Excellence Program from the Spanish State Research Agency.grant no. MDM-20170720

Hybridized plexcitonic states have unique properties which have been widely studied in recent decades in many research fields targeted at both fundamental science and innovative applications. However, to make these applications come true one needs to ensure the stabilization and preservation of electronic states and optical transitions in hybrid nanostructures, especially under the influence of external stressors, in regimes, that have not yet been comprehensively investigated. The present work shows that the nanohybrid system, composed of plasmonic nanoparticles and J-aggregates of organic molecules, displays outstanding resistance to harsh environmental stressors such as temperature, pH and strong light irradiation as well as demonstrates long-term stability and processability of the nanostructures both in weak and strong coupling regimes. These findings contribute to a deeper understanding of the physicochemical properties of plexcitonic nanoparticles and may find important implications for the development of potential applications in optoelectronics, optical imaging and chemo-bio-sensing and, in general, in the field of optical materials science., Authors acknowledge the financial support from the Ministry of Education and Science of the Russian Federation (grant no. 14.Y26.31.0011). Y. R. acknowledges the support from the Basque Government (grant no. IT1164-19). M. G. acknowledges support from the Basque Government (PIBA 2018-34), and Diputación Foral de Guipúzcoa (RED 2018, RED 2019). A. S. I. acknowledges the Maria de Maeztu Units of Excellence Programme – Grant No. MDM-2017-0720 Ministry of Science, Innovation and Universities.

Although high-quality gold nanorods can be routinely synthesized, within a wide range of sizes and aspect ratios, a similar level of control has not been reached for silver nanorods. Whereas seeded-growth processes have been developed, the reported methods have not met sufficient interest, mainly because of limited quality, particularly when small size (short diameter) and small aspect ratios are targeted. In the surfactant-driven seeded growth of gold nanorods, the success of the synthesis is largely dependent on the quality and stability of the seeds, and thus related methods have been reported for the seeded growth of Ag nanorods, using penta-twinned Au nanorods and bipyramids as seeds. However, Ag nanorods with diameters of >30 nm are consistently obtained, restricting their potential applications. We report the preparation of high-quality silver nanorods, using either small bipyramids or small decahedra as seeds, with special attention to the location of the seeds, either at the center (bipyramids) or at one end (decahedra) of the resulting nanorods.

Strong exciton–plasmon interaction enables effective control of the photonic properties of hybrid organic–inorganic nanostructures encompassing light absorption, scattering and luminescence. Whereas the manifestations of light-matter interactions in the absorption and scattering are reasonably well understood their relation to the luminescence as well as luminescence properties themselves in strongly coupled plexcitonic hybrids is still largely underexplored especially for a system with a complex mechanism of hybridisation of states. Here we report on investigation of the interaction between localized and hybridized plasmons in gold nanostars and excitons in J-aggregates under ambient conditions. Our findings demonstrate the quality performance of the formed plexciton system with multiple hybridization channels in terms of the parameters of strong coupling, such as Rabi splitting (230 meV), coupling-strength-to-transition energy ratio (0.07), and cooperativity (2.03). The results of time-resolved experiments elucidate the observed enhanced spontaneous emission rate with regard to the Purcell effect, whose value was estimated from the extinction spectra of the strongly coupled plexciton system., Financial supports from Projects PID2019-111772RB-I00 of the Spanish MINECO and the Ministry of Science and Higher Education of the Russian Federation (Grant No. 14.Y26.31.0011) are acknowledged. Y. R. acknowledges the support from the Basque Government (grant no. IT1164-19). P.S. and I.N acknowledge support from the Russian Science Foundation (grant no. 21-79-30048) of the part of this work related to nanomaterials manufacturing and functionalisation. I.N. acknowledges support from the Université de Reims Champagne-Ardenne. A.S.-I. acknowledges the Maria de Maeztu Units of Excellence Program from the Spanish State Research Agency (Grant No. MDM-2017-0720).

Plasmonic nanoparticles (PNPs) can significantly modify the optical properties of nearby organic molecules and thus present an attractive opportunity for sensing applications. However, the utilization of PNPs in conventional absorption, fluorescence, or Raman spectroscopy techniques is often ineffective due to strong absorption background and light scattering, particularly in the case of turbid solutions, cell suspensions, and biological tissues. Here we show that nonmagnetic organic molecules may exhibit magneto-optical response due to binding to a PNP. Specifically, we detect strong magnetic circular dichroism signal from supramolecular J-aggregates, a representative organic dye, upon binding to silver-coated gold nanorods. We explain this effect by strong coupling between the J-aggregate exciton and the nanoparticle plasmon, leading to the formation of a hybrid state in which the exciton effectively acquires magnetic properties from the plasmon. Our findings are fully corroborated by theoretical modeling and constitute a novel magnetic method for chemo- and biosensing, which (upon adequate PNP functionalization) is intrinsically insensitive to the organic background and thus offers a significant advantage over conventional spectroscopy techniques., We acknowledge financial support from Project Fis2016.80174-P (PLASMOQUANTA) from MINECO (Ministerio de Economia y Competitividad). L.L.-M. acknowledges funding from the European Research Council (ERC Advanced Grant 267867, Plasmaquo).

Semiconductor quantum dots (QDs) are known for their ability to exhibit multiphoton emission caused by recombination of biexcitons (BX). However, the quantum yield (QY) of BX emission is low due to the fast Auger process. Plasmonic nanoparticles (PNPs) provide an attractive opportunity to accelerate BX radiative recombination. Here, we demonstrate the PNPs induced distance-controlled enhancement of BX emission of single QDs. Studying the same single QD before and after its integration with the PNPs, we observed a plasmon-mediated increase in the QY of BX emission. Remarkably, the enhancement of BX emission remains pronounced even at distances of 170 nm. We attribute this effect to efficient coupling, which results in the trade-off between resonance energy transfer from QD to gold nanorods and the Purcell effect at small QD-PNP separations and the predominant influence of the Purcell effect at longer distances. Our findings constitute a reliable approach to managing the efficiency of multiexciton emission over a wide span of distances, thus paving the way for new applications., The authors acknowledge the financial support from the Ministry of Education and Science of the Russian Federation (Grant 14.Y26.31.0011). Y.R. acknowledges support from MINECO (Ministerio de Economiá y Competitividad, Spain), Project Fis2016.80174-P (PLASMOQUANTA).

The hydrophobic collapse is a structural transition of grafted polymer chains in a poor solvent. Although such a transition seems an intrinsic event during clustering of polymer-stabilized nanoparticles in the liquid phase, it has not been resolved in real time. In this work, we implemented a microfluidic 3D-flow-focusing mixing reactor equipped with real-time analytics, small-angle X-ray scattering (SAXS), and UV–vis–NIR spectroscopy to study the early stage of cluster formation for polystyrene-stabilized gold nanoparticles. The polymer shell dynamics obtained by in situ SAXS analysis and numerical simulation of the solvent composition allowed us to map the interaction energy between the particles at early state of solvent mixing, 30 ms behind the crossing point. We found that the rate of hydrophobic collapse depends on water concentration, ranging between 100 and 500 nm/s. Importantly, we confirmed that the polymer shell collapses prior to the commencement of clustering.

Semiconductor quantum dots (QDs) are known for their unique photophysical properties and, in particular, their ability to multiphoton emission caused by recombination of biexcitons. However, the luminescence quantum yield of biexciton states is relatively low due to the fast Auger non-radiative process. Plasmonic nanoparticles can significantly accelerate the radiative rate of QDs. In this study we demonstrate the distance-controlled enhancement of the biexciton emission of single CdSe/ZnS/CdS/ZnS QDs due to their coupling with gold nanorods. We explain this enhancement as the distancedependent trade-off between the energy transfer and the Purcell effect. Our findings constitute a reliable approach to managing the efficiency of multiphoton emission over a wide span of distances.

It is commonly agreed that the crystalline structure of seeds dictates the crystallinity of final nanoparticles in a seeded-growth process. Although the formation of monocrystalline particles does require the use of single-crystal seeds, twin planes may stem from either single-or polycrystalline seeds. However, experimental control over twin-plane formation remains difficult to achieve synthetically. Here, we show that a careful interplay between kinetics and selective surface passivation offers a unique handle over the emergence of twin planes (in decahedra and triangles) during the growth over single-crystalline gold nanoparticles of quasi-spherical shape. Twinning can be suppressed under conditions of slow kinetics in the presence of silver ions, yielding single-crystalline particles with high-index facets.

The anisotropic morphology of gold nanorods (AuNRs) has been shown to lead to nonuniform ligand distribution and preferential etching through their tips. We have recently demonstrated that this effect can be achieved by biocatalytic oxidation with hydrogen peroxide, catalyzed by the enzyme horseradish peroxidase (HRP). We report here that modification of AuNRs with thiol-containing organic molecules such as glutathione and thiocholine hinders enzymatic AuNR etching. Higher concentrations of thiol-containing molecules in the reaction mixture gradually decrease the rate of enzymatic etching, which can be monitored by UV–vis spectroscopy through changes in the AuNR longitudinal plasmon band. This effect can be applied to develop novel optical assays for acetylcholinesterase (AChE) activity. The biocatalytic hydrolysis of acetylthiocholine by AChE yields thiocholine, which prevents enzymatic AuNR etching in the presence of HRP. Additionally, the same bioassay can be used for the detection of nanomolar concentrations of AChE inhibitors such as paraoxon and galanthamine.

Nanoparticle assemblies can be investigated in 3 dimensions using electron tomography. However, it is not straightforward to obtain quantitative information such as the number of particles or their relative position. This becomes particularly difficult when the number of particles increases. We propose a novel approach in which prior information on the shape of the individual particles is exploited. It improves the quality of the reconstruction of these complex assemblies significantly. Moreover, this quantitative Sparse Sphere Reconstruction approach yields directly the number of particles and their position as an output of the reconstruction technique, enabling a detailed 3D analysis of assemblies with as many as 10 000 particles. The approach can also be used to reconstruct objects based on a very limited number of projections, which opens up possibilities to investigate beam sensitive assemblies where previous reconstructions with the available electron tomography techniques failed.

Gold and silver nanoclusters aggregates have gained significant attention as their optical properties and chemical stability surpasses those of individual nanoclusters. Here, we present a systematic investigation of aggregation-induced changes of morphology and optical properties of glutathione-stabilized silver-doped gold nanoclusters (AuAg NCs). We show that the silver-doped clusters have the ability to spontaneously aggregate in solution, but in order to stabilize their structure and enhance the one-photon (1 P) and two-photon (2 P) properties we used poly(allylamine hydrochloride) (PAH) matrix. This resulted in obtaining NCs superstructures having narrow size distribution and efficient 1 P and 2 P excited photoluminescence.

A thorough understanding of the thermal stability and potential reshaping of anisotropic gold nanostars is required for various potential applications. Combination of a tomographic heating holder with fast tilt series acquisition has been used to monitor temperature-induced morphological changes of Au nanostars. The outcome of our 3D investigations can be used as an input for boundary element method simulations, enabling us to investigate the influence of reshaping on the nanostars’ plasmonic properties. Our work leads to a better understanding of the mechanism behind thermal reshaping. In addition, the approach presented here is generic and can hence be applied to a wide variety of nanoparticles made of different materials and with arbitrary morphology.

The efficacy of drug delivery and other nanomedicine-related therapies largely relies on the ability of nanoparticles to reach the target organ. However, when nanoparticles are injected into the bloodstream, their surface is instantly modified upon interaction with blood components, principally with proteins. It is well known that a dynamic and multi-layered protein structure is formed spontaneously on the nanoparticle upon contact with physiological media, which has been termed protein corona. Although several determinant factors involved in protein corona formation have been identified from in vitro studies, specific relationships between the nanomaterial synthetic identity and its ensuing biological identity under realistic in vivo conditions remain elusive. We present here a detailed study of in vivo protein corona formation after blood circulation of anisotropic gold nanoparticles (nanorods and nanostars). Plasmonic gold nanoparticles of different shapes and sizes were coated with polyethyleneglycol, intravenously administered in CD-1 mice and subsequently recovered. The results from gel electrophoresis and mass spectrometry analysis revealed the formation of complex protein coronas, as early as 10 minutes post-injection. The total amount of protein adsorbed onto the particle surface and the protein corona composition were found to be affected by both the particle size and shape.

The presence of iodide ions during the growth of gold nanorods strongly affects the shape of the final products, which is proposed to be due to selective iodide adsorption on certain crystallographic facets. Therefore, a detailed structural and morphological characterization of the starting rods is crucial toward understanding this effect. Electron tomography is used to determine the crystallographic indices of the lateral facets of gold nanorods, as well as those present at the tips. Based on this information, density functional theory calculations are used to determine the surface and interface energies of the observed facets and provide insight into the relationship between the amount of iodide ions in the growth solution and the final morphology of anisotropic gold nanoparticles.

A limiting factor of solvent-induced nanoparticle self-assembly is the need for constant sample dilution in assembly/disassembly cycles. Changes in the nanoparticle concentration alter the kinetics of the subsequent assembly process, limiting optical signal recovery. Herein, we show that upon confining hydrophobic nanoparticles in permeable silica nanocapsules, the number of nanoparticles participating in cyclic aggregation remains constant despite bulk changes in solution, leading to highly reproducible plasmon band shifts at different solvent compositions.

Pt nanoparticles play an essential role in a wide variety of catalytic reactions. The activity of the particles strongly depends on their three-dimensional (3D) structure and exposed facets, as well as on the reactive environment. High-resolution electron microscopy has often been used to characterize nanoparticle catalysts but unfortunately most observations so far have been either performed in vacuum and/or using conventional (2D) in situ microscopy. The latter however does not provide direct 3D morphological information. We have implemented a quantitative methodology to measure variations of the 3D atomic structure of nanoparticles under the flow of a selected gas. We were thereby able to quantify refaceting of Pt nanoparticles with atomic resolution during various oxidation–reduction cycles. In a H2 environment, a more faceted surface morphology of the particles was observed with {100} and {111} planes being dominant. On the other hand, in O2 the percentage of {100} and {111} facets decreased and a significant increase of higher order facets was found, resulting in a more rounded morphology. This methodology opens up new opportunities toward in situ characterization of catalytic nanoparticles because for the first time it enables one to directly measure 3D morphology variations at the atomic scale in a specific gaseous reaction environment.

Three dimensional (3D) characterization of structural defects in nanoparticles by transmission electron microscopy is far from straightforward. We propose the use of a dose-efficient approach, so-called multimode tomography, during which tilt series of low and high angle annular dark field scanning transmission electron microscopy projection images are acquired simultaneously. In this manner, not only reliable information can be obtained concerning the shape of the nanoparticles, but also the twin planes can be clearly visualized in 3D. As an example, we demonstrate the application of this approach to identify the position of the seeds with respect to the twinning planes in anisotropic gold nanoparticles synthesized using a seed mediated growth approach.

The three-dimensional (3D) atomic structure of nanomaterials, including strain, is crucial to understand their properties. Here, we investigate lattice strain in Au nanodecahedra using electron tomography. Although different electron tomography techniques enabled 3D characterizations of nanostructures at the atomic level, a reliable determination of lattice strain is not straightforward. We therefore propose a novel model-based approach from which atomic coordinates are measured. Our findings demonstrate the importance of investigating lattice strain in 3D.

Resumen del trabajo presentado a la 19th International Conference on Transparent Optical Networks (ICTON), celebrada en Girona (España) del 2 al 6 de julio de 2017., We report our recent results of investigation of the interactions between localized plasmons in gold nanorods and excitons in J-aggregates. We were able to track an anticrossing behavior of the hybridized modes both in the extinction and in the photoluminescence spectra of this hybrid system. We identified the nonlinear optical behavior of this system by transient absorption spectroscopy. Finally using magnetic circular dichroism spectroscopy, we show that nonmagnetic organic molecules exhibit magneto-optical response due to binding to a plasmonic nanoparticles. In our experiments, we also studied the effect of detuning as well as the effect of off- and on resonance excitation on the hybrid states.

Trabajo presentado a la 3rd International Conference on Applications of Optics and Photonics, celebrado en Faro (Portugal) del 8 al 12 de mayo de 2017., We investigated the interactions between localized plasmons in gold nanorods and excitons in J-aggregates and were able to track an anticrossing behavior of the hybridized modes both in the extinction and in the photoluminescence spectra of this hybrid system. We identified the nonlinear optical behavior of this system by transient absorption spectroscopy. Finally using magnetic circular dichroism spectroscopy we showed that nonmagnetic organic molecules exhibit magneto-optical response due to binding to a plasmonic nanoparticles. In our experiments we also studied the effect of detuning as well as the effect of off- and on resonance excitation on the hybrid states., We acknowledge financial support from Project Fis2016.80174-P (PLASMOQUANTA) from MINECO (Ministerio de Economía y Competitividad). L.L.-M. acknowledges funding from the European Research Council (ERC Advanced Grant 267867, Plasmaquo). This study was supported by the Ministry of Education and Science of the Russian Federation, grant no. 14.Y26.31.0011.

Metal nanoparticles with a dumbbell-like geometry have plasmonic properties similar to those of their nanorod counterparts, but the unique steric constraints induced by their enlarged tips result in distinct geometries when self-assembled. Here, we investigate gold dumbbells that are assembled into dimers within polymeric micelles. A single-particle approach with correlated scanning electron microscopy and dark-field scattering spectroscopy reveals the effects of dimer geometry variation on the scattering properties. The dimers are prepared using exclusively achiral reagents, and the resulting dimer solution produces no detectable ensemble circular dichroism response. However, single-particle circular differential scattering measurements uncover that this dimer sample is a racemic mixture of individual nanostructures with significant positive and negative chiroptical signals. These measurements are complemented with detailed simulations that confirm the influence of various symmetry elements on the overall peak resonance energy, spectral line shape, and circular differential scattering response. This work expands the current understanding of the influence self-assembled geometries have on plasmonic properties, particularly with regard to chiral and/or racemic samples which may have significant optical activity that may be overlooked when using exclusively ensemble characterization techniques.

Strong coupling of plasmons and excitons can form hybrid states, the so-called “plexcitons”. Although plasmons have a low quality factor, the exceptionally high coupling strength with molecular aggregates, in particular J-aggregates, allows the realization of strong interaction. Despite several studies in recent years showing the formation of plexcitonic states, their nature, especially at very short times, is still insufficiently investigated. In this article, we identify the nonlinear optical behavior of plexcitons formed on gold nanorods coated with J-aggregated cyanine molecules at short times by transient absorption spectroscopy and a simple Lorentz oscillator model. We control the spectral overlap of the two resonances and analyze the effect of detuning as well as the effect of off- and on resonance excitation on the hybrid states. We demonstrate that at ultrashort time scales plexcitons show tunable plasmonic and excitonic nonlinear performance according to the hybridization model. In a first approach, we discover a way to optically manipulate the quality factor and study the effects on the coupled hybrid states. As a second approach, we find that the coupling strength can also be influenced on an ultrashort time scale in the strong coupling regime when plexcitons are excited., This work has been financially supported by the ERC Advanced Grant HYMEM and the Bavarian State Ministry of Science, Research, and Arts through “Solar Technologies Go Hybrid” (SolTech) as well as through Projects FIS2013-41184-P and MAT2013-46101-R of the Spanish Ministry of Economy and Competitiveness (MINECO).

We experimentally and theoretically investigate the interactions between localized plasmons in gold nanorods and excitons in J-aggregates under ambient conditions. Thanks to our sample preparation procedure we are able to track a clear anticrossing behavior of the hybridized modes not only in the extinction but also in the photoluminescence (PL) spectra of this hybrid system. Notably, while previous studies often found the PL signal to be dominated by a single mode (emission from so-called lower polariton branch), here we follow the evolution of the two PL peaks as the plasmon energy is detuned from the excitonic resonance. Both the extinction and PL results are in good agreement with the theoretical predictions obtained for a model that assumes two interacting modes with a ratio between the coupling strength and the plasmonic losses close to 0.4, indicative of the strong coupling regime with a significant Rabi splitting estimated to be ∼200 meV. The evolution of the PL line shape as the plasmon is detuned depends on the illumination wavelength, which we attribute to an incoherent excitation given by decay processes in either the metallic rods or the J-aggregates., We acknowledge financial support from Projects FIS2013-41184-P and MAT2013-46101-R of the Spanish Ministry of Economy and Competitiveness (MINECO) and ETORTEK project NANOGUNE’14. R.E. acknowledges funding as Fellow Gipuzkoa of the Gipuzkoako Foru Aldundia through Feder Funds of the European Union “Una manera de hacer Europa”.

International audience; Gold nanoparticles are prime candidates for cancer thermotherapy. However, while the ultimate target for nanoparticle-mediated photothermal therapy is the cancer cell, heating performance has not previously been evaluated in the tumoral environment. A systematic investigation of gold nanostar heat-generating efficiency in situ is presented: not only in cancer cells in vitro but also after intratumoral injection in vivo. It is demonstrated that (i) in aqueous dispersion, heat generation is governed by particle size and exciting laser wavelength; (ii) in cancer cells in vitro, heat generation is still very efficient, but irrespective of both particle size and laser wavelength; and (iii) heat generation by nanostars injected into tumors in vivo evolves with time, as the nanostars are trafficked from the extracellular matrix into endosomes. The plasmonic heating response thus serves as a signature of nanoparticle internalization in cells, bringing the ultimate goal of nanoparticle-mediated photothermal therapy a step closer.

International audience; The acoustic vibrations of metal nanoparticles encapsulated in a dielectric shell (Ag@SiO2) were investigated using a time-resolved femtosecond technique. The measured vibration periods significantly differ from those predicted for the bare metal cores and, depending on the relative core and shell sizes, were found to be either larger or smaller than them. These results show that the vibration of the whole core-shell particle is excited and detected. Moreover, vibrational periods are in excellent agreement with the predictions of a model based on continuum thermoelasticity. However, such agreement is obtained only if a good mechanical contact of the metal and dielectric parts of the core-shell particle is assumed, providing a unique way to probe this contact in multimaterial or hybrid nano-objects.

This paper describes the processing of silver nanoparticle doped poly(vinylidene fluoride). The effect of the dopant concentration on the alpha- to beta-phase transformation of the polymer as well as in the morphological, thermal, optical and dielectric properties of the nanocomposites was investigated. Spherical silver nanoparticles were incorporated into the poly(vinylidene fluoride) polymeric matrix by the solvent casting method, with different Ag concentrations. Well-dispersed Ag nanoparticles act as nucleation centers, increasing the degree of crystallinity of the nanocomposites. Homogeneous dispersion of silver nanoparticles is demonstrated through the presence of surface plasmon resonance absorption in the nanocomposites. The alpha- to beta-phase transformation was achieved in the polymer matrix and a maximum of approximately equal to 70% of beta-PVDF was reached at 80 degrees C and a stretching ratio of 400%. The dielectric constant of the nanocomposites increases with increasing metal nanoparticle concentration, up to approximately equal to 26 at 0.020 wt% Ag content. The alpha- to beta-phase transformation affects both the dielectric response and the surface plasmon resonance.

Surface and interface control is fundamentally important for crystal growth engineering, catalysis, surface-enhanced spectroscopies, and self-assembly, among other processes and applications. Understanding the role of ligands in regulating surface properties of plasmonic metal nanocrystals during growth has received considerable attention. However, the underlying mechanisms and the diverse functionalities of ligands are yet to be fully addressed. In this contribution, we report a systematic study of ligand-mediated interface control in seeded growth of gold nanocrystals, leading to diverse and exotic nanostructures with an improved surface enhanced Raman scattering (SERS) activity. Three dimensional transmission electron microscopy revealed an intriguing gold shell growth process mediated by the bifunctional ligand 1,4-benzenedithiol (BDT), which leads to a unique crystal growth mechanism as compared to other ligands, and subsequently to the concept of interfacial energy control mechanism. Volmer–Weber growth mode was proposed to be responsible for BDT-mediated seeded growth, favoring the strongest interfacial energy and generating an asymmetric island growth pathway with internal crevices/gaps. This additionally favors incorporation of BDT at the plasmonic nanogaps, thereby generating strong SERS activity with a maximum efficiency for a core-semishell configuration obtained along seeded growth. Numerical modeling was used to explain this observation. Interestingly, the same strategy can be used to engineer the structural diversity of this system, by using gold nanoparticle seeds with various sizes and shapes, and varying the [Au3+]/[Au0] ratio. This rendered a series of diverse and exotic plasmonic nanohybrids such as semishell-coated gold nanorods, with embedded Raman-active tags and Janus surface with distinct surface functionalities. These would greatly enrich the plasmonic nanostructure toolbox for various studies and applications such as anisotropic nanocrystal engineering, SERS, and high-resolution Raman bioimaging or nanoantenna devices. ASTAR (Agency for Sci., Tech. and Research, S’pore) Published version

A new type of gold nanoparticle—called “spiky nanodumbbells”—is introduced. These particles combine the anisotropy of nanorods with sharp nanoscale features of nanostars, which are important for SERS applications. Both the morphology and the optical response of the particles are characterized in detail, and the experimental results are compared with FDTD simulations, showing good agreement., This work has been funded by the European Research Council (ERC Advanced Grant #267867 Plasmaquo). M.K.S. and J.A. acknowledge funding from the ETORTEK project nanoIKER of the Department of Industry of the Government of the Basque Country and project FIS2010–19609-C02–01 of the Spanish Ministry of Innovation.

The dimensions of spherical plasmonic clusters strongly depend on the concentration of their building blocks. We show here that for binary clusters consisting of nanoparticle building blocks with different sizes and relative content, the overall size of the clusters remains constant. However, in the presence of a good solvent the clusters undergo fission to produce smaller units with homogenously distributed building blocks.

Thumbnail image of graphical abstract To investigate nanoassemblies in three dimensions, electron tomography is an important tool. For large nanoassemblies, it is not straightforward to obtain quantitative results in three dimensions. An optimized acquisition technique, incoherent bright field scanning transmission electron microscopy, is combined with an advanced 3D reconstruction algorithm. The approach is applied to quantitatively analyze large nanoassemblies in three dimensions.

The optical absorption of one-dimensional photonic crystal based resonators containing different types of gold nanoparticles is controllably modified by means of the interplay between planar optical cavity modes and localized surface plasmons. Spin-casting of metal oxide nanoparticle suspensions was used to build multilayered photonic structures that host (silica-coated) gold nanorods and spheres. Strong reinforcement and depletion of the absorptance was observed at designed wavelength ranges, thus proving that our method provides a reliable means to modify the optical absorption originated at plasmonic resonances of particles of arbitrary shape and within a wide range of sizes. These observations are discussed on the basis of calculations of the spatial and spectral dependence of the optical field intensity within the multilayers. © 2012 American Chemical Society., H.M. thanks the Ministry of Science and Innovation for funding under Grants MAT2011-23593 and CONSOLIDER CSD2007-00007, as well as Junta de Andalucía for Grants FQM3579 and FQM5247. L.M.L.-M. acknowledges receipt of an ERC Advanced Grant (PLASMAQUO). SEM and TEM characterization were performed at CITIUS, and we are grateful for its support

Hydrophobic interactions constitute one of the most important types of nonspecific interactions in biological systems, which emerge when water molecules rearrange as two hydrophobic species come close to each other. The prediction of hydrophobic interactions at the level of nanoparticles (Brownian objects) remains challenging because of uncontrolled diffusive motion of the particles. We describe here a general methodology for solvent-induced, reversible self-assembly of gold nanoparticles into 3D clusters with well-controlled sizes. A theoretical description of the process confirmed that hydrophobic interactions are the main driving force behind nanoparticle aggregation.

In the formation of colloidal molecules, directional interactions are crucial for controlling the spatial distribution of the building blocks. Anisotropic nanoparticles facilitate directional clustering via steric constraints imposed by each specific shape, thereby restricting assembly along certain directions. We show in this Letter that the combination of patchiness (attraction) and shape (steric hindrance) allows assembling gold nanodumbbell building blocks into crosslike dimers with well-controlled interparticle distance and relative orientation. Steric hindrance between interacting dumbbell-like particles opens up a new synthetic approach toward low-symmetry plasmonic clusters, which may significantly contribute to understand complex plasmonic phenomena.

Novel colloidal composites have been designed to incorporate multiple functionalities that allow optical detection, magnetic manipulation, molecular trapping, and thermal response. Such particles are made of gold nanoparticle cores covered by a thin layer of metallic nickel and a poly(N-isopropylacrylamide) (pNIPAM) shell. While the gold cores provide efficient optical response through localized surface plasmon resonances, nickel allows external magnetic manipulation and the pNIPAM shell can be swollen or collapsed as a function of temperature, thus allowing capture and release of various types of molecules.

International audience; The optical extinction spectra of single silver nanoparticles coated with a silica shell were investigated in the size range 10-50 nm. Measurements were performed using the spatial modulation spectroscopy technique which permits independent determination of both the size of the metal nanoparticle under study and the width of its localized surface plasmon resonance (LSPR). These parameters can thus be directly correlated at a single particle level for the first time. The results show a linear increase of the width of the LSPR with the inverse diameter in the small size regime (less than 25 nm). For these nanoparticles of well-controlled environment, this can be ascribed to quantum confinement of electrons or, classically, to increase of the electron surface scattering processes. The impact of this effect was measured quantitatively and compared to the predictions by theoretical models.

The synthesis of gold nanorods requires the presence of symmetry-breaking and shape-directing additives, among which bromide ions and quaternary ammonium surfactants have been reported as essential. As a result, hexadecyltrimethylammonium bromide (CTAB) has been selected as the most efficient surfactant to direct anisotropic growth. One of the difficulties arising from this selection is the low solubility of CTAB in water at room temperature, and therefore the seeded growth of gold nanorods is usually performed at 25 degrees C or above, which has restricted so far the analysis of kinetic effects derived from lower temperatures. We report a systematic study of the synthesis of gold nanorods from pentatwinned seeds using hexadecyltrimethylammonium chloride (CTAC) as the principal surfactant and a low concentration of bromide as shape-directing agent. Under these conditions, the synthesis can be performed at temperatures as low as 8 degrees C, and the corresponding kinetic effects can be studied, resulting in temperature-controlled aspect ratio tunability.

ACS photonics 7(3), 646-652 (2020). doi:10.1021/acsphotonics.9b01418, Published by ACS, Washington, DC

Silver is arguably the best plasmonic material in terms of optical performance. However, wide application of Ag and Ag-containing nanoparticles is usually hindered by two major drawbacks, namely, chemical degradation and cytotoxicity. We report herein a synthetic method for highly monodisperse polymer-coated Ag nanorods, which are thereby protected against external stimuli (oxidation, light, heat) and are noncytotoxic to various cell lines. The monodispersity of Ag nanorods endows them with narrow plasmon bands, which are tunable into the near-infrared biological transparency window, thus facilitating application in bioanalytical and therapeutic techniques. We demonstrate intracellular surface-enhanced Raman scattering (SERS) imaging using Ag nanorods encoded with five different Raman reporter molecules. Encoded Ag nanorods display long-term stability in terms of size, shape, optical response, and SERS signal. Our results help eliminate concerns of instability and cytotoxicity in the application of Ag-containing nanoparticles with enhanced optical response, toward the development of bioapplications.