Cédric Volcke

High efficiency amine functionalization of cycloolefin polymer surfaces for biodiagnostics

Point-of-care (POC) diagnostics implementing microfluidic technology on single use disposable plastic chips has potential applications in personalized medicine, clinical diagnostics and global health. However, the challenges in commercializing POC devices must be addressed. Immobilization of biomolecules to plastic chips through appropriate surface functionalization is a key issue for the fabrication of new generation biomedical diagnostic devices. The most important requirements for a practicable surface functionalization process are speed, control and reliability. Plasma-based methods can meet these criteria. A single step, solventless, ecofriendly and high throughput nature of plasma processing makes them highly attractive. Here we demonstrate the efficient surface functionalization of a next-generation biosensor material, a chemically inert cycloolefin polymer (COP). The plasma formation of a surface-bound aminated siloxane network from mixed aminopropyltriethoxysilane and ethylenediamine precursors allowed us to form a well-adherent film with an exceptionally high degree of amine functionalization. We deduce that the siloxane was the critical component for radical insertion into the COP and for building a stable network to support the reactive amine functionalities. We present a full physical and chemical characterization of the films, including a detailed study of their swelling in water, using an array of surface analytical techniques: X-ray photoelectron spectroscopy, X-ray reflectivity, reflection infra-red spectroscopy, atomic force microscopy (AFM) and fluorophore binding reactions. We demonstrate an original approach for qualitatively analyzing the distribution of amine functionalities by counting surface-bound functionalized silica nanoparticles in the AFM. The relative contributions from covalent (specific) and non-covalent (non-specific) reaction chemistry assessed using 3′-fluorescein-labeled ssDNA attachment showed that the non-specific binding could be reduced significantly according to the particular feed gas mixture used to prepare the coating. A reaction mechanism has been proposed for the deposition of amine functionalities on COP plastic and also for enhancing the amine functionalities that affect the non-specific binding significantly.

Titanium modified with layer-by-layer sol-gel tantalum oxide and an organodiphosphonic acid: A coating for hydroxyapatite growth

Titanium and its alloys are widely used in surgical implants due to their appropriate properties like corrosion resistance, biocompatibility, and load bearing. Unfortunately when metals are used for orthopedic and dental implants there is the possibility of loosening over a long period of time. Surface modification is a good way to counter this problem. A thin tantalum oxide layer obtained by layer-by-layer (LBL) sol-gel deposition on top of a titanium surface is expected to improve biocorrosion resistance in the body fluid, biocompatibility, and radio-opacity. This elaboration step is followed by a modification of the tantalum oxide surface with an organodiphosphonic acid self-assembled monolayer, capable of chemically binding to the oxide surface, and also improving hydroxyapatite growth. The different steps of this proposed process are characterized by surfaces techniques like contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM).

Deposition of chemically reactive and repellent sites on biosensor chips for reduced non-specific binding.

The performances of new polymeric materials with excellent optical properties and good machinability have led the biomedical diagnostics industry to develop cheap disposable biosensor platforms appropriate for point of care applications. Zeonor, a type of cycloolefin polymer (COP), is one such polymer that presents an excellent platform for biosensor chips. These polymer substrates have to be modified to have suitable physico-chemical properties for immobilizing proteins. In this work, we have demonstrated the amine functionalization of COP substrates, by plasma enhanced chemical vapour deposition (PECVD), through codeposition of ethylene diamine and 3-aminopropyltriethoxysilane precursors, for building chemistries on the plastic chip. The elemental composition, adhesion, ageing and reactivity of the plasma polymerized film were examined. The Si-O functionality present in amino silane contributed for a good interfacial adhesion of the coating to COP substrates and also acted as a network building layer for plasma polymerization. Wet chemical modification was then carried out on the amine functionalized chips to create chemically reactive isothiocyanate sites and protein repellent fluorinated sites on the same chip. The density of the reactive and repellent sites was altered by choosing appropriate mixtures of homofunctional phenyldiisothiocyanate (PDITC), pentafluoroisothiocyanate (5FITC) and phenylisothiocyanate (PITC) compounds. By tailoring the density of reactive binding sites and protein repellent sites, the non-specific binding of ssDNA has been decreased to a significant extent.

Total internal reflection sum-frequency generation spectroscopy and dense gold nanoparticles monolayer: a route for probing adsorbed molecules

We show that sum-frequency generation spectroscopy performed in the total internal reflection configuration (TIR–SFG) combined with a dense gold nanoparticles monolayer allows us to study, with an excellent signal to noise ratio and high signal to background ratio, the conformation of adsorbed molecules. Dodecanethiol (DDT) was used as probe molecules in order to assess the potentialities of the approach. An enhancement of more than one order of magnitude of the SFG signals arising from the adsorbed species is observed with the TIR geometry compared to the external reflection one while the SFG non-resonant contribution remains the same for both configurations. Although further work is required to fully understand the origin of the SFG process on nanoparticles, our work opens new possibilities for studying nanostructures.

Plasma Surface Modification of Cyclo-olefin Polymers and Its Application to Lateral Flow Bioassays

The modification of cyclo-olefin polymer Zeonor by plasma-enhanced chemical vapor deposition to form a silica-like surface and evaluation of its application for lateral flow bioassays applications are discussed in this study. The SiOx layer was extensively characterized using contact angle measurements, atomic force microscopy, and Fourier transform infrared spectroscopy in attenuated total internal reflectance mode where the presence of a uniform SiOx film was clearly identified. The SiOx modification resulted in a surface with enhanced wettability and excellent fluidic properties when combined with a hot-embossed micropillar capillary fill-based substrate. The SiOx surface also had the ability to accelerate the clotting of human plasma, which may have application in certain types of blood coagulation assays.

Morphology of polystyrene films deposited by RF plasma

A new plasma reactor, set up with a large planar inductively coupled source, is used for the first time to deposit a polymer coating (pPS) from a styrene monomer. This work is devoted to the relationship between external plasma parameters and substrate topography, and pPS coating morphology, which is investigated by scanning electron microscopy and atomic force microscopy. Stainless steel, gold and glass surfaces are used as substrates. It is clearly demonstrated that the film morphology can be controlled by adjustment of RF input power, pressure. The analysis performed further reveals that the pPS films characteristics strongly depend on the substrate topography and its electrical potential during the discharge. Finally, the plasma duration also strongly influences the morphology of the films. The morphologies obtained include smooth films without any specific feature, worm‐like structures, particles (nanometer‐ and micrometer‐sized) associated along preferential directions and randomly distributed particles (micrometer‐sized). The intrinsic topography of the substrate influences the film structure in the case of thin films (thickness lower than about 100 nm).

Special features in self-assembled monolayer revealed by functionalised STM tips

Some functional groups in self-assembled monolayers have recently been identified in STM images, due to the chemical modification of gold tips [1]. In those studies, different molecules presenting different functional groups were investigated, resolving several molecular organizations [1-2, 4]. In this paper, we aimed at demonstrating that such chemically modified STM tips can be used to investigate phenomenon routinely observed with standard Pt/Ir tips, such as domain boundary dynamics in hexadecanol SAMs. It also allows transitory features to be identified. Moreover, rarely observed phenomena are also presented below, i.e. bilayers composed of wax esters molecules physisorbed at the phenyloctane/graphite interface.