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The identification of new colloidal sol-gel routes for the preparation of actinide oxides, which have a homogeneous and accessible porosity that can easily be impregnated by any concentrated actinide solution, opens new perspectives for the preparation of homogeneous nuclear fuel for minor actinide transmutation. This homogeneity allows us to avoid "hot spot" formation due to the local accumulation of more fissile elements. Here, we report the preparation of macro-microporous ThO

International audience; SU-8 photoresist polymer is widely used in the fabrication of microdevices. However, for biological applications , the problem of efficiently modifying SU-8 surfaces without perturbing roughness has not been successfully resolved. We present UV/ozone (UVO) surface pre-treatment as an effective method to increase the hydrophilicity of SU-8 films without affecting surface roughness, thus improving specific covalent binding of bio-molecules. We demonstrate that 30 s UVO treatment suffices to create carboxyl groups at the surface that can then be used for high density binding of molecules via amide bond formation. We further demonstrate that a two-step surface modification where the surface is first protected with an ethylene glycol monolayer leads to an increase in binding specificity. Finally, to illustrate the controlled binding and accessibility of immobilized molecules, we show three cycles of reversible interactions between anti-tamra antibody and tamra-cadaverine immobilized on the surface of SU-8.

We report on a new accurate investigation tool whose principle is that of a Michelson interferometer with a broadband source, namely a phase-sensitive optical low-coherence interferometer, used to interrogate an optical micro-resonator based sensor for label-free biosensing applications. This set-up, which is able to provide the amplitude and also the phase of the guided mode in a single measurement, is also used to evaluate the performances of the micro-resonators. The best vertically coupled polymer racetrack micro-resonator fabricated displays a Q-factor higher than 38 000 and a finesse of 21 at 1527.7 nm when immersed in deionized water. The association of the phase-sensitive optical low coherence interferometer and the vertically coupled polymer micro-resonator in an opto-fluidic cell for biosensing applications was tested and allowed the detection of a concentration of glucose in water solution around 0.23 mg ml−1.

Cuboid-shaped organic microcavities containing a pyrromethene laser dye and supported upon a photonic crystal have been investigated as an approach to reducing the lasing threshold of the cavities. Multiphoton lithography facilitated fabrication of the cuboid cavities directly on the substrate or on the decoupling structure, while similar structures were fabricated on the substrate by UV lithography for comparison. Significant reduction of the lasing threshold by a factor of ~30 has been observed for cavities supported by the photonic crystal relative to those fabricated on the substrate. The lasing mode spectra of the cuboid microresonators provide strong evidence showing that the lasing modes are localized in the horizontal plane, with the shape of an inscribed diamond., Comment: 11 pages, 11 figures, 25 references

We measured the far-field emission patterns in three dimensions of flat organic dye microlasers using a solid angle scanner. Polymer-based microcavities of ribbon shape (i.e., Fabry-Perot type) were investigated. Out of plane emission from the cavities was observed, with significant differences for the two cases of resonators either fully supported by the substrate or sustained by a pedestal. In both cases, the emission diagrams are accounted for by a model combining diffraction at the cavity edges and reflections from the substrate., Copyright (2013) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics

We previously demonstrated that vertically-coupled polymer microring resonators are good candidates as transducers in label-free biosensing instruments, for several reasons: good optical performances, low production costs, excellent biocompatibility and state-of-the-art surface sensitivity. We later presented the association of our original opto-electronic setup to microfluidics to perform homogeneous optofluidic detection, using glucose solutions to characterize the behavior of the microring transducer. In parallel, the same transducer devices have been associated to another detection scheme, phase-sensitive OLCI, with promising results.

In this paper we report on the design and fabrication of polymeric microracetracks optical resonators for optofluidic label-free biosensing. In the domain of optical integrated devices, polymer materials offer the advantages of low cost, easy fabrication, low scattering loss on waveguide sidewalls, and high coupling efficiency to optical fibres and waveguides. Moreover, for biochemical sensing, polymer surfaces can be easily modified to immobilize a wide choice of target molecules. Polymers are also well compatible with microfluidic circuits, favoring the insertion of photonic circuits into optofluidic cells. The vertical coupling configuration, in which resonators are vertically coupled to the buried bus waveguide, presents several advantages in comparison with the lateral coupling configuration, particularly in the context of optofluidic biosensors. Polymeric microracetracks were fabricated using the SU-8 negative photoresist and the CYTOP fluorinated polymer, using a combination of a simple near UV lithography and reactive ion etching technology. Vertically coupled microracetracks immersed in deionized water display high Q-factors (> 35000) and finesse up to 25. Surface sensing experiments performed with these microresonators using TAMRA-cadaverine as a test molecule, which can be quantified through fluorescence analysis, demonstrated a very low detection limit of 0.22 attogram.

International audience; We report on the efficient design and fabrication of polymeric microracetrack optical resonators for label-free biosensing purposes. Vertically-coupled microresonators immersed in deionised water display high Q-factors (>35000) and finesses up to 25. A surface sensing experiment performed with these microresonators using 5-TAMRA cadaverine as a test molecule demonstrated both the high sensitivity and low detection limit of our device.

The electro-optical Pockels response from a single non-centrosymmetric nanocrystal is reported. High sensitivity to the weak electric-field dependent nonlinear scattering is achieved through a dedicated imaging interferometric microscope and the linear dependence of electro-optical signal upon the applied field is checked. Using different incident light polarization states, a priori random spatial orientation of the crystal can be inferred. The electro-optical response from a nanocrystal provides local subwavelength sensor of quasi-static electric fields with potential applications in physics and biology. It also leads to a new sub-wavelength microscopy towards the nanoscale investigation of interesting phenomena such as nanoferroelectricity.

Two-dimensional microlasers are generating interest for their potential applications, as bio-and chemiosensors and as building blocks for optical telecommunications [1]. For many practical purposes it is crucial to conceive and demonstrate microcavities exhibiting a very directional and furthermore controllable output emission. Among various cavity shapes, the stadium is a simple prototype pattern which is known to be highly directional with emissions in four directions [2–5].

International audience; Non-specific binding to biosensor surfaces is a major obstacle to quantitative analysis of selective retention of analytes at immobilized target molecules. Although a range of chemical antifouling monolayers has been developed to address this problem, many macromolecular interactions still remain refractive to analysis due to the prevalent high degree of non-specific binding. In this manuscript we explore the dynamic process of the formation of self-assembled monolayers and optimize physical and chemical properties thus reducing considerably non-specific binding while maintaining the integrity of the immobilized biomolecules. As a result, analysis of specific binding of analytes to immobilized target molecules is significantly facilitated.

The structural changes of ammonium diuranate (ADU) microspheres, prepared by the sol-gel route via internal gelation, were investigated during thermal treatments in oxidative and reducing conditions. In particular, in-situ simultaneous thermogravimetric analyses and in-situ high-temperature scanning electron microscopy investigations were carried out on un-doped ADU microspheres, and ADU microspheres doped with 10 mol% neodymium or 10 mol% cerium. Calcination in air caused the surface of the particles to crack, but with increasing temperature up to 900 °C some healing, and additionally, shrinkage occurred. The extent of the fractures and the amount of shrinkage was, however, significantly more pronounced in a particle prepared with a tetravalent Ce precursor, as compared to particles prepared with a trivalent Nd or Ce precursor. The macroscopic behaviour could be related to the release of volatile decomposition products and the calcined compositions were identified as (Ln-doped) α-U3O8 by X-ray powder diffraction. During thermal treatment in reducing conditions a transition from a (Ln-doped) α-U3O8 phase to a (Ln-doped) UO2±x phase was observed. After exposure to a hydrogen containing gas mixture, this transition occurred rapidly in un-doped particles, and in particles prepared with trivalent Nd or Ce dopant precursors at 700 °C. Despite the fast reduction reaction, severe fractures appeared in the particles above temperatures of 850 °C, indicating that such behaviour is mainly attributed to sintering effects and less to the phase transition. In contrast, a more delayed reduction reaction was observed in particles prepared with a tetravalent dopant precursor and the described effects appeared less severe.