Bimetallic Au/Ag core–shell cuboid nanoparticles (NPs) exhibit a complex plasmonic response dominated by a dipolar longitudinal mode and higher-order transverse modes in the near-UV, which may be exploited for a range of applications. In this paper, we take advantage of the strong signature of these modes in the NP ultrafast transient optical response, measured by pump-probe transient absorption (TA) spectroscopy, to explore the NP vibrational landscape. The fast Fourier transform analysis of the TA dynamics reveals specific vibration modes in the frequency range 15–150 GHz, further studied by numerical simulations based on the finite element method. While bare Au nanorods exhibit extensional and breathing modes, the bimetallic NPs undergo more complex motions, involving the displacement of facets, edges and corners. The amplitude and frequency of these modes are shown to depend on the Ag shell thickness, as the silver load modifies the NP aspect ratio and mass. Moreover, the contributions of the vibrational modes to the experimental TA spectra are shown to vary with the probe laser wavelength at which the signal is monitored. Using the combined simulations of the NP elastic and optical properties, we elucidate this influence by analyzing the effect of the mechanisms involved in the acousto-plasmonic coupling.

Noble metal nanoparticles exhibit localized plasmon resonance modes that span the visible and near-infrared spectral ranges and have many applications. Modifying the size, shape, and composition of the nanoparticles changes the number of modes and their properties. The characteristics of these modes are transiently affected when illuminating the nano-objects with ultrashort laser pulses. Here, we synthesize core-shell gold-silver nanocuboids and measure their spectral signature in the stationary and ultrafast transient regimes. Their dipolar transverse mode vanishes with increasing Ag-shell thickness, while higher-order modes grow in the near-ultraviolet range where no plasmon resonance can be generated with single noble metal nanoparticles. These higher-energy modes are associated with sharp spectral variations of the ultrafast transient light extinction by the bimetallic nanocuboids. By carrying out a theoretical investigation, we break down the different contributions to this response and

BackgroundHER2-overexpressing metastatic breast cancers are challenging practice in oncology when they become resistant to anti-HER2 therapies such as trastuzumab. In these clinical situations, HER2-overexpression persists in metastatic localizations, and can thus be used for active targeting using innovative therapeutic approaches. Functionalized gold nanoparticles with anti-HER2 antibody can be stimulated by near-infrared light to induce hyperthermia.MethodsHere, hybrid anti-HER2 gold nanoshells were engineered for photothermal therapy to overcome trastuzumab resistance in HER2-overexpressing breast cancer xenografts.ResultsWhen gold nanoshells were administered in HER2-tumor xenografts, no toxicity was observed. A detailed pharmacokinetic study showed a time-dependent accumulation of gold nanoshells within the tumors, significantly greater with functionalized gold nanoshells at 72h. This enabled us to optimize the treatment protocol and irradiate the mice when the anti-HER2 gold nanoshells had accumulated most in the tumors. After weekly injections of anti-HER2 gold nanoshells, and repeated irradiations with a femtosecond-pulsed laser over four weeks, tumor growth was significantly inhibited. Detailed tissue microscopic analyses showed that the tumor growth inhibition was due to an anti-angiogenic effect, coherent with a preferential distribution of the nanoshells in tumor microvessels. We also showed a direct tumor cell effect with apoptosis and inhibition of proliferation, coherent with an immune-mediated targeting of tumor cells by anti-HER2 nanoshells.ConclusionThis preclinical study thus supports the use of anti-HER2 gold nanoshells and photothermal therapy to overcome trastuzumab resistance in HER2-overexpressing breast cancer.

We present a new example of a mononuclear iron(ii) complex exhibiting a correlated spin-crossover (SCO) transition and strong fluorescence, whose coordination sphere is saturated, for the first time, by six phosphorescent ligands. The interplay between SCO and light emission properties in the thermal region of the spin transition was investigated by means of magnetic, fluorescence, optical absorption and optical microscopy measurements on a single crystal. Overall, the results show an excellent correlation between fluorescence and magnetic data of the present gradual transition, indicating an extreme sensitivity of the optical activity of the ligand to the spin state of the active iron(ii) ions. These results open the way for conceiving new prototypes of pressure and temperature sensors based on this synergy between SCO and luminescence properties. In particular, the fact that cooperative SCO material is not a prerequisite for obtaining such synergetic effects, is useful for the design of thin films or nanoparticles, in which the cooperativity is reduced, for appropriate implementation in nanosized devices to enhance the sensing properties at the nanoscale.

•Designing homogeneous lighting system for a photobioreactor in undergone.•Bright and dull side reflectivities of household aluminum foil are measured.•They have dramatically different diffuse and specular components.•Total reflectivity is the same over the spectrum for both sides.•These measurement are applied to achieve uniform intensity lighting.

Univ. Brest, CNRS, CEMCA, 6 Avenue Vict Cedex 3, France. E-mail: Smail.Triki@univGroupe d'Etude de la Matière Condensée, Saint Quentin, Université Paris-Saclay, 45 cedex, France. E-mail: Kamel.boukheddaden Department of Chemistry and Biochemistry, Parkway, Norman, OK 73019, USA Instituto de Ciencia Molecular (ICMol), Universidad de Valencia, C/Catedrático José † Electronic supplementary information 1565195. For ESI and crystallographic dat DOI: 10.1039/c9sc02331c Cite this: Chem. Sci., 2019, 10, 6791

Artificial materials at optical frequencies have raised a strong interest in the last years, including photonic metamaterials, graded photonic crystals, and simple gradient index structures. The main common objective of these approaches is achieving a tight control of the electromagnetic guided-wave fields to play with light properties and propose versatile optical functions. In this general context, this work is focused on gradual photonic crystals (GPhCs) working in the diffraction regime, i.e. close to the photonic crystal (PhC) bandgap.

The use of a birefringent graded photonic crystal (GPhC) is proposed for the realization of an efficient polarization beam splitter. This approach allows decoupling the two functions of efficient light injection for both polarizations and TE/TM beam splitting. A smooth light polarization splitting is naturally achieved due to the different curved trajectories followed within the graded medium by the TE and TM waves. A 160 nm operating bandwidth with insertion loss around 1 dB and interpolarization crosstalk below -15 dB is predicted by a finite difference time domain simulation. The unusually exploited electromagnetic phenomena are experimentally evidenced by scanning near-field optical measurements performed on samples fabricated using the silicon on insulator photonics technology. These experimental works open perspectives for the use of birefringent GPhCs to manage polarization diversity in silicon photonic circuits.

The transition between the long-wavelength and the short-wavelength regimes of light propagation in two-dimensional graded photonic crystal is investigated using a hyperspectral near-field scanning microscope. The experiments show an invariant quantity of only 1.78 times the lattice period as the criterion for the possible application of homogenization theories. These results are discussed in light of Fourier decomposition of the electromagnetic Bloch waves, and a physical interpretation of the observed transition between the two light propagation regimes is proposed. These results indicate the robustness of the homogenization approaches and suggest that the sharp transition between the two light propagation regimes could be profitably combined in graded optical artificial materials.

The transition between the long-wavelength and the short-wavelength regimes of light propagation in all-dielectric metamaterials is experimentally probed using a hyperspectral near-field scanning microscope technique. Our measurements lead to an invariant quantity “λ/n” of only 1.78 times the dielectric lattice period as the criterion for the possible application of homogenization theories.

Photonic metamaterials made of graded photonic crystals operating near the bandgap frequency region are proposed for field manipulation around l=1.5μm. Proof-of-concept structures have been studied using Hamiltonian optics and FDTD simulation, fabricated, and characterized using farfield optical measurements. Experimental results are in good agreement with predictions, showing the interest of graded photonic crystals as an (ultra-low loss) alternative solution to the use of metamaterials combining dielectric and metallic materials with sub-wavelength unit cells.

Experimental results on light bending effect in a non-homogenizable graded photonic crystals operating at optical wavelengths are presented. A square lattice photonic crystal made with a two-dimensional chirp of the air-hole filling factor is exploited to produce this bending effect in a near bandgap frequency range. Experimental results are in good agreement with the prediction that had been performed using the equations of Hamiltonian optics and Finite-Difference Time-Domain simulations. This experimental demonstration performed in one particular configuration opens opportunities for light manipulation using a combination of unusual dispersive phenomena in PhCs and additional degrees of freedom brought by a generalized two-dimensional chirp of PhCs lattice parameters. This approach is also an alternative solution to the use of photonic metamaterials combining dielectric and metallic materials with sub-wavelength unit cells.

Using a scanning near-field optical microscope operating with a hyperspectral detection scheme, we report the direct observation of the mirage effect within an on-chip integrated artificial material made of a two dimensional graded photonic crystal. The light rainbow due to the material dispersion is quantified experimentally and quantitatively compared to three dimensional plane wave assisted Hamiltonian optics predictions of light propagation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4756902]

The dispersive properties of planar photonic crystals (PhCs) have been envisaged for years. In particular, the superprism effect has been considered to obtain a strong influence of input beam conditions (e. g. wavelength or input angle) on the light group velocity direction, enabling the design and fabrication of on-chip infra-red spectrometers and integrated optical demultiplexers. We extend here the properties of PhCs to the study of graded photonic crystals (GPhCs) made of a two-dimensional chirp of lattice parameters and show that GPhCs enable solving several drawbacks of dispersive PhCs like the beam divergence issues or the need of long preconditioning regions to precompensate beam diffraction effects. The proposed approach is applied to a square lattice air-hole PhC with a gradual filling factor that was fabricated using e-beam lithography and ICP etching techniques. A nearly-constant 0.25 mu m/nm spatial dispersion is demonstrated for a 60 mu m square GPhC structure in the 1470-1600nm spectral range without noticeable spatial or spectral spreading. Moreover, contrary to PhC superprism structures, a linear dispersion is obtained in the considered wavelength range.

Experimental results on light bending in a non-homogenizable graded photonic crystal operating at optical wavelengths are presented in this paper. A square lattice silicon on insulator photonic crystal made of a two-dimensional chirp of the air-hole filling factor is exploited to produce the bending effect in a near bandgap frequency range. The sensitivity of light paths to wavelength tuning is also exploited to show demultiplexing capability with low insertion loss (<2dB) and low crosstalk (~-20dB). This experimental demonstration opens opportunities for light manipulation using a generalized two-dimensional chirp of photonic crystal lattice parameters. It also constitutes an alternative solution to the use of photonic metamaterials combining dielectric and metallic materials with sub-wavelength unit cells.

An analytical method is proposed for the design of all-dielectric metamaterials at optical frequencies. It is applied to the design of broadband weakly-open in-plane light trajectories like logarithmic spirals in the silicon on insulator photonics technology which could be hardly described by the use of coordinate transforms.

An analytical method is proposed for the design of all-dielectric metamaterials at optical frequencies as an alternative to the formalism of transformation optics. It is applied to the design of broadband weakly-open in-plane light trajectories like logarithmic spirals in the silicon on insulator photonics technology which could be hardly described by the use of coordinate transforms.

Artificial optical materials made of graded photonic crystals or photonic metamaterials are a promising route to design versatile optical functionalities in the near-infrared. We report here the design, fabrication, and characterization of a planar gradual photonic crystal in the silicon on insulator photonics. Unusual light propagation phenomena consisting in light bending towards low long-range averaged refractive index regions are directly evidenced using an original hyperspectral scanning near-field technique. Giant dispersion properties of the gradual structure around 0.25µm/nm are reported.