Olivier Soppera

Photopolymerization and photostructuring of molecularly imprinted polymers for sensor applications--a review.

Molecularly Imprinted Polymers (MIP) were prepared by photochemical route. Photoinduced polymerization was used to achieve the preparation of the MIP and at the same time spatially controlled irradiation allowed shaping the material to confer it an optical function useful for interrogation. Such route significantly simplifies the integration of MIP for sensor applications. Specific photopolymerizable MIP were designed for photopolymerization at different wavelengths and advanced methods of photopatterning were used including optical near-field, interference or self-guiding lithography. Photopatterning appears thereby as one of the most suitable methods for patterning MIP at the micro and nano scale, directly on the transducer surface.

Opposite responses of cells and bacteria to micro/nanopatterned surfaces prepared by pulsed plasma polymerization and UV-irradiation.

Chemically and topographically patterned surfaces have high potential as model surfaces for studying cell and bacteria responses to surface chemistry and surface topography at a nanoscale level. In this work, we demonstrated the possibility to combine pulsed plasma polymerization and UV-irradiation to obtain topographical patterns and chemical patterns perfectly controlled at microlateral resolution and sub-micrometer depth level. Biological experiments were conducted using human osteoprogenitor cells and Escherichia coli K12. Proliferation and orientation of cells and bacteria were analyzed and discussed according to the size and the chemistry of the features. This work showed interesting opposite behavior of bacteria compared to eukaryotic cells, in response to the surface chemistry and to the surface topography. This result may be particularly useful on medical implants. From a methodological point of view, it highlighted the importance of working with versatile and well-characterized surfaces before and after sterilization. It also points out the relevance and the necessity of analyzing eukaryotic cell and bacteria adhesion in parallel way.

Quantitative Analysis of Localized Surface Plasmons Based on Molecular Probing

We report on the quantitative characterization of the plasmonic optical near-field of a single silver nanoparticle. Our approach relies on nanoscale molecular molding of the confined electromagnetic field by photoactivated molecules. We were able to directly image the dipolar profile of the near-field distribution with a resolution better than 10 nm and to quantify the near-field depth and its enhancement factor. A single nanoparticle spectral signature was also assessed. This quantitative characterization constitutes a prerequisite for developing nanophotonic applications.

Fabry-Perot refractometer based on an end-of-fiber polymer tip

A micrometric Fabry-Perot refractometer based on an end-of-fiber polymer tip is proposed. The fiber tip, with a length of 36 mum, was fabricated by self-guiding photopolymerization. The two-wave interferometric operation was achieved by combining the light waves generated at the interface between the single-mode fiber and the polymer tip, and at the fiber tip end (Fresnel reflection). The Fabry-Perot interferometer is coherence addressed and heterodyne interrogated, resulting into a liquid refractive index resolution of approximately 7.5x10(-4).

A Versatile Fiber‐Optic Fluorescence Sensor Based on Molecularly Imprinted Microstructures Polymerized in Situ

A method using laser-induced photopolymerization was developed to generate highly selective fiber optic sensors in a few seconds that are based on molecularly imprinted polymer (MIP) microtips. The fluorescence detection signal was enhanced using gold nanoparticles. The sensor also detects nonfluorescent analytes when a fluorescent signaling monomer is incorporated into the MIP.

Spatially controlled synthesis of silver nanoparticles and nanowires by photosensitized reduction

The present paper reports on the spatially controlled synthesis of silver nanoparticles (NPs) and silver nanowires by photosensitized reduction. In a first approach, direct photogeneration of silver NPs at the end of an optical fiber was carried out. Control of both size and density of silver NPs was possible by changing the photonic conditions. In a further development, a photochemically assisted procedure allowing silver to be deposited at the surface of a polymer microtip was implemented. Finally, polymer tips terminated by silver nanowires were fabricated by simultaneous photopolymerization and silver photoreduction. The silver NPs were characterized by UV-visible spectroscopy and scanning electron microscopy.

Holographic Molecularly Imprinted Polymers for Label‐Free Chemical Sensing

Holographic molecularly imprinted polymer films for the use in chemical sensors are obtained in one step through photopolymerization with interfering laser beams. This results in hierarchical structuring at four length scales: micrometer-scale patterning of millimeter- to centimeter- size polymer objects with holographic optical properties, exhibiting nanometer-scale porosity and specific molecular recognition properties at the molecular scale through self-assembly. Specific binding of the target analyte testosterone is measured by diffraction analysis.

New insights into photoinduced processes in hybrid sol–gel glasses containing modified titanium alkoxides

Hybrid organic–inorganic sol–gel compounds have been widely used for the design of new optical devices, since they combine the characteristics of both glasses and polymers and improve the properties of the final material. Hybrid precursors in which both phases are chemically grafted are of increasing interest: volume shrinkage is minimized and phase separation can be kept below the level of Rayleigh scattering, thus leading to highly transparent glasses. Polymerizable acrylate or methacrylate functions grafted onto modified silicone alkoxides can react ia a free-radical mechanism initiated either by heating or UV-light. Considerable attention has already been focused on the chemical mechanisms involved in the construction of the inorganic network. However, no extensive study of the organic part of the process has so far been conducted. This paper points out the characteristics of the photopolymerization process taking place in hybrid sol–gel materials. In particular, the influence of inorganic moieties on the photopolymerization kinetics was studied by UV and real time FTIR spectroscopy. Particular interest was focused on the incorporation of alkoxymetals that are usually added to improve the optical and physical properties of the final material. The role of the titanium component in the photopolymerization process is emphasized. The results provide insights into processes leading to simultaneous formation of interpenetrating organic–inorganic networks and are of crucial importance for the generation of optical devices.

Plasmon-based free-radical photopolymerization: effect of diffusion on nanolithography processes.

This Article interrogates the mechanisms responsible for nanoscale photopolymerization induced by confined and enhanced electromagnetic fields. Surface plasmon dipolar resonance of individual Ag nanoparticles was used as an optical near-field source to locally trigger the reaction of a photopolymerizable formulation. Laser excitation of the nanoparticles embedded in the formulation reproducibly generates polymer features with typical dimensions ranging from 2 nm to a few tens of nanometer. We have determined the physicochemical parameters and mechanisms controlling the spatial extent of the photopolymerization process. We found that the diffusion of the dye is the main process limiting the polymerization reaction, as opposed to what is observed at the microscale with an equivalent chemical system. This approach demonstrates that plasmon-based polymerization can achieve true nanometer scale resolution and also provides a unique opportunity to investigate photochemistry at this length scale.

Photoredox catalysis using a new iridium complex as an efficient toolbox for radical, cationic and controlled polymerizations under soft blue to green lights

A new iridium complex (nIr) was designed and investigated as a photoinitiator catalyst for radical and cationic polymerizations upon very soft irradiations (lights ranging from 457 to 532 nm). A ring-opening polymerization (ROP) of an epoxy monomer was easily promoted through the interaction between nIr and an iodonium salt (Iod) upon light. The addition of N-vinylcarbazole (NVK) enhances the performance. In radical polymerization, nIr can be efficient in combination with phenacyl bromide (PBr) and optionally an amine: these photoinitiating systems work according to an original oxidative cycle and a regeneration of nIr is observed. A control of the methyl methacrylate polymerization (conducted under a 462 nm light) with 1.2–1.6 polydispersity indexes was displayed. Surface modifications by direct laser write was also easily carried out for the first time through surface re-initiation experiments, i.e. the dormant species being reactivated by light in the presence of nIr; the polymer surfaces were analyzed by XPS. The chemical mechanisms were examined through laser flash photolysis, NMR, ESR and size exclusion chromatography experiments.