Ligand-Induced Anisotropy of the Two-Photon Luminescence of Spherical Gold Particles in Solution Unraveled at the Single Particle Level

Here we report on the visible luminescence properties of individual spherical gold particles in solution, obtained by two-photon excited fluorescence correlation spectroscopy and by an original dual Rayleigh-fluorescence method, correlating the Rayleigh scattering and the luminescence fluctuations of the same particle. The results demonstrate that the power needed to observe the two-photon excited visible luminescence depends on the illuminated particle and that the corresponding emission is anisotropic at low power. These observations combined with the evolution of the dynamics of the luminescence with respect to excitation power are interpreted by the presence of unique emissive surface states that are randomly switched off and on by the heat-induced movement of the molecular coating. These characteristics, which remain hidden in macroscopic experiments, have important implications with respect to the potential use of the particles as labels in two-photon imaging in aqueous samples

Fluorescence correlation spectroscopy reveals strong fluorescence quenching of FITC adducts on PEGylated gold nanoparticles in water and the presence of fluorescent aggregates of desorbed thiolate ligands

Colloidal gold particles functionalised with oligoethylene-glycolated disulfide ligands and fluorescent moieties derived from fluorescein isothiocyanate (FITC) have been prepared and studied in aqueous suspension using fluorescence correlation spectroscopy (FCS). FCS probes the dynamics of the particles at the single object level, and reveals the desorption of fluorescent ligands which subsequently aggregate into larger (slower diffusing) objects. Cross-correlation spectroscopy of the FITC fluorescence and the Rayleigh-Mie scattering (RM-FCCS) of the gold cores shows that the only detectable fluorescent objects are free ligands and aggregates not associated with a gold particle. The fluorescence of bound fluorophores is quenched making their fluorescence too weak to be detected. FCS and RM-FCCS are useful tools for characterising functionalised noble metal particles in solution, under conditions similar to those used in optical bio-imaging. Desorption of thiolates from gold nanoparticles needs to be taken into account when working with these materials at low concentration

MariX, an advanced MHz-class repetition rate X-ray source for linear regime time-resolved spectroscopy and photon scattering

The need of a fs-scale pulsed, high repetition rate, X-ray source for time-resolved fine analysis of matter (spectroscopy and photon scattering) in the linear response regime is addressed by the conceptual design of a facility called MariX (Multi-disciplinary Advanced Research Infrastructure for the generation and application of X-rays) outperforming current X-ray sources for the declared scope. MariX is based on the original design of a two-pass two-way superconducting linear electron accelerator, equipped with an arc compressor, to be operated in CW mode (1 MHz). MariX provides FEL emission in the range 0.2–8 keV with 108 photons per pulse ideally suited for photoelectric effect and inelastic X-ray scattering experiments. The accelerator complex includes an early stage that supports an advanced inverse Compton source of very high-flux hard X-rays of energies up to 180 keV that is well adapted for large area radiological imaging, realizing a broad science programme and serving a multidisciplinary user community, covering fundamental science of matter and application to life sciences, including health at preclinical and clinical level

Gamma Factory at CERN – novel research tools made of light

We discuss the possibility of creating novel research tools by producing and storing highly relativistic beams of highly ionised atoms in the CERN accelerator complex, and by exciting their atomic degrees of freedom with lasers to produce high-energy photon beams. Intensity of such photon beams would be by several orders of magnitude higher than offered by the presently operating light sources, in the particularly interesting gamma-ray energy domain of 0.1-400 MeV. In this energy range, the high-intensity photon beams can be used to produce secondary beams of polarised electrons, polarised positrons, polarised muons, neutrinos, neutrons and radioactive ions. New research opportunities in a wide domain of fundamental and applied physics can be opened by the Gamma Factory scientific programme based on the above primary and secondary beams.Comment: 12 pages; presented by W. Placzek at the XXV Cracow Epiphany Conference on Advances in Heavy Ion Physics, 8-11 January 2019, Cracow, Polan

Molécule unique, nanotube de carbone et exaltation Raman

La spectroscopie Raman fournit une analyse détaillée de la structure chimique d'un objet, à température ambiante. La section efficace de diffusion Raman d'un objet petit est souvent faible et son signal ne pourra être détecté sans utiliser un processus d'exaltation efficace de la diffusion. Cet article décrit quelques avancées dans le domaine de l'exaltation de surface de la diffusion Raman. Il est illustré par des résultats expérimentaux que nous avons obtenus sur des molécules uniques. Parfois, le signal de certains objets petits peut être détecté sans effet d'exaltation supplémentaire, comme le montre l'exemple de nanotubes remplis, dits peapods

The ABCD matrices for reflection and refraction for any incident angle and surface

International audienceA method to derive the ABCD matrices for reflection and refraction for any diopter under arbitrary incident angle is developed. The result is benchmarked on a commercial software for an optical system compound of two cylindrical lenses. It is used to simulate the general astigmatism and calculate the resulting Orbital Angular Momentum of a laser beam that propagate through a pair of cylindrical lenses. It more generally useful to ease and simplify such kind of simulations in any optical system by avoiding use of complicated commercial softwares

Détection de molécules individuelles par microscopie à un et à deux photons : étude de la réaction de complexation d'une sonde calcique

Nous présentons les premiers résultats de l'étude des propriétés de sondes calciques par microscopie biphotonique. En présence d'ions calcium, ces sondes participent à une réaction de complexation-décomplexation qui les porte alternativement dans un état fluorescent et un état noir. La dynamique temporelle de leur émission est étudiée par spectroscopie de corrélation de fluorescence, à l'échelle de la molécule unique