Numerous works are based on the design, the elaboration and the study of the optical properties of gold nanoprobes for
potential applications in biotechnologies (bioimaging, biosensing). Among all the possible shapes, it appears that sharp
gold nanostructures exhibit interesting features due to the strong filed generated at their tips ends, making them very
sensitive to the surrounding medium. Here we describe a complete study of PEGylated gold nanoparticles : nanostars and
bipyramids as potential agents for bioimaging. The nanoprobes are first prepared in high yield before functionalization
with a biocompatible polymer. Then, the PEGylated gold nanoparticles are incubated with melanoma B16-F10 cells and
observed using Dark-field microscopy. Results show that the biocompatible gold nanoparticles are easily internalized and
most of them localized within the cells.
We review our work on hybrid gold nanoparticles that are optimized for their bright fluorescence and photobleaching resistance. Our first goal in using gold nanoparticles is to load a large density of photoactive molecules onto a biocompatible nanoplatform. Our second goal is to optimize the molecule-gold nanoparticle interaction to improve the photoactive properties, in particular their photobleaching resistance. In this project gold nanoparticles have typical dimensions in the 50-100 nm that are suitable for in vivo imaging and photodynamic therapy. Their geometrical shapes include nanoshell, spheres, rods, bipyramids and stars.
The development of near-infrared dyes for third order nonlinear optical applications and particularly for optical power limiting at telecommunications wavelengths triggered the revival of old dyes like polymethine dyes featuring an odd number of carbon atoms. Currently numerous research endeavor is focused on the understanding of their spectroscopy in solution and in the solid state in close relationship with their electronic structure. In this context, the dramatic effect of the counter ion on the heptamethine optical properties was highlighted depending on the dissociating character of the media. The unusual consideration of this parameter allows us to explore the so-called “cyanine limit” and to finely tune the heptamethine absorption in view of future use as dopant in a material for optical limiting applications.
We review our work on several strategies to elaborate multifunctional nanoparticules for two-photon imaging or/and
photodynamic therapy. Our first strategy is based on the incorporation of two-photon hydrophobic fluorophors in bio-compatible
pluronic micelles using the mini-emulsion technique. Our second strategy is based on fluorescent organic
nanocrystal grown in silicate spheres. These core-shell hybrid nanoparticles are obtained by a spray-drying process from
sol-gel solutions. Our third strategy consists in the encapsulation of hydrophilic molecules in the water core of gold
nanospheres. They are obtained by a stabilized emulsion in biphasic liquid-liquid medium without surfactant.
Optical limiting materials are developed for applications in protection of optical sensors against laser aggressions. We have studied functionalised macrocycles (thiacalixarenes) and alkynylplatinum(II) derivatives for optical limiting applications. Glass materials based on alkynylplatinum(II) derivatives and macrocycles were prepared through the sol-gel process. The molecular species were grafted to the matrix in order to maximise the concentration and the stability of the final solid-state material. The glass materials were cut and polished to approximately 1.5 mm. The glass materials show broadband optical limiting in the visible wavelength region, for nanosecond laser pulses.
Alkynyl platinum derivatives and thiacalixarenes were trapped in solid transparent matrices prepared by the sol-gel process. By using functionalyzed silicon alkoxides, molecular species were grafted to the gel matrix giving a high doping concentration and chemically stable materials. In this communication we present broadband optical limiting performance in the visible wavelength region observed in the prepared materials.
YAG optical planar waveguide was elaborated through sol-gel method. Acetate-alkoxide (YAG-I) and 2-alkoxides (YAG-II) methods were used for the sol preparations. The as-deposited layers were characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD), m-lines, spectroscopy (MLS) Rutherford Backscattering Spectroscopy (RBS) and waveguide Raman spectroscopy (WRS). No intermediate phases were observed for both synthesis routes. In comparison, (YAG-II) layers presented a better adherence than YAG-I to SiO<sub>2</sub> substrate, a higher refractive index and allowed to form a pure phase of YAG at lower temperature and short heat duration (900°C for 10min). However, the interdiffusion of Al and Si ions were detected to influence the refractive index improvement by heat treatments. The propagation loss of the fabricated YAG thin films in amorphous phase can be as low as 1.5±0.3 dB/cm.