Charles Agnès

Supercapacitor/biofuel cell hybrids based on wired enzymes on carbon nanotube matrices: autonomous reloading after high power pulses in neutral buffered glucose solutions

We report an original setup using carbon nanotube matrices as supercapacitors where redox enzymes serve for continuous charging of the capacitors. High currents can be delivered under short pulse discharges. This supercapacitor/biofuel cell hybrid system remains stable for at least 40 000 pulses of 2 mW.

Freestanding redox buckypaper electrodes from multi-wall carbon nanotubes for bioelectrocatalytic oxygen reduction via mediated electron transfer

An efficient and easy way of designing free standing redox buckypaper electrodes via the elegant combination of multi-walled carbon nanotubes (MWCNTs) and a bis-pyrene derivative is reported. This bis-pyrene 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid (bis-Pyr-ABTS) acts as a cross-linker between the nanotubes and assures the formation of a mechanically reinforced buckypaper, obtained by a classical filtration technique of a MWCNT suspension in the presence of bis-Pyr-ABTS. In addition, the ABTS derivative assures a mediated electron transfer to laccase. The electroactive buckypapers were characterized in terms of morphology, conductivity, and electrochemical properties. Two setups were evaluated. The first consisted of the immobilization and wiring of laccase enzymes via an inclusion complex formation between the hydrophobic cavity of laccase and the pyrene groups of bis-Pyr-ABTS that are not π-stacked to the nanotubes. The second approach was to evaluate the mediated electron transfer using laccase in solution. For this setup, the developed mediator electrodes demonstrated high performances with maximum currents up to 2 mA ± 70 μA and an excellent operational stability for two weeks with daily one hour discharges using refreshed laccase solutions.

Distinctive Glial and Neuronal Interfacing on Nanocrystalline Diamond

Direct electrode/neuron interfacing is a key challenge to achieve high resolution of neuronal stimulation required for visual prostheses. Neuronal interfacing on biomaterials commonly requires the presence of glial cells and/or protein coating. Nanocrystalline diamond is a highly mechanically stable biomaterial with a remarkably large potential window for the electrical stimulation of tissues. Using adult retinal cell cultures from rats, we found that glial cells and retinal neurons grew equally well on glass and nanocrystalline diamond. The use of a protein coating increased cell survival, particularly for glial cells. However, bipolar neurons appeared to grow even in direct contact with bare diamond. We investigated whether the presence of glial cells contributed to this direct neuron/diamond interface, by using purified adult retinal ganglion cells to seed diamond and glass surfaces with and without protein coatings. Surprisingly, these fully differentiated spiking neurons survived better on nanocrystalline diamond without any protein coating. This greater survival was indicated by larger cell numbers and the presence of longer neurites. When a protein pattern was drawn on diamond, neurons did not grow preferentially on the coated area, by contrast to their behavior on a patterned glass. This study highlights the interesting biocompatibility properties of nanocrystalline diamond, allowing direct neuronal interfacing, whereas a protein coating was required for glial cell growth.

New one step functionalization of polycrystalline diamond films using amine derivatives

Diamond received tremendous interest for analytical sciences due to its intrinsic properties. However, the analytical perception of chemical environment requires surface functionalization that brings selectivity to the detection event. Thereby, many works focused on diamond modification using chemical or biochemical entities. We proposed here, a new and straightforward methodology for diamond (bio)functionalization. This method involves the chemical reaction between (bio)chemical entities presenting a primary amine moiety, used as grafting site, and hydrogenated diamond surface. This reaction allows in one step to modify diamond surface whatever its doping level and its crystalline quality. The effectiveness of this new method is exposed here through the grafting of one redox species, ferrocene, and of one biochemical, biotin. The impacts of both functionalization duration and pH are investigated and the robustness of the formed bond is demonstrated owing to biotin-avidin coupling.

High Sensitivity of Diamond Resonant Microcantilevers for Direct Detection in Liquids As Probed by Molecular Electrostatic Surface Interactions

Resonant microcantilevers have demonstrated that they can play an important role in the detection of chemical and biological agents. Molecular interactions with target species on the mechanical microtransducers surface generally induce a change of the beams bending stiffness, resulting in a shift of the resonance frequency. In most biochemical sensor applications, cantilevers must operate in liquid, even though damping deteriorates the vibrational performances of the transducers. Here we focus on diamond-based microcantilevers since their transducing properties surpass those of other materials. In fact, among a wide range of remarkable features, diamond possesses exceptional mechanical properties enabling the fabrication of cantilever beams with higher resonant frequencies and Q-factors than when made from other conventional materials. Therefore, they appear as one of the top-ranked materials for designing cantilevers operating in liquid media. In this study, we evaluate the resonator sensitivity performances of our diamond microcantilevers using grafted carboxylated alkyl chains as a tool to investigate the subtle changes of surface stiffness as induced by electrostatic interactions. Here, caproic acid was immobilized on the hydrogen-terminated surface of resonant polycrystalline diamond cantilevers using a novel one-step grafting technique that could be also adapted to several other functionalizations. By varying the pH of the solution one could tune the -COO(-)/-COOH ratio of carboxylic acid moieties immobilized on the surface, thus enabling fine variations of the surface stress. We were able to probe the cantilevers resonance frequency evolution and correlate it with the ratio of -COO(-)/-COOH terminations on the functionalized diamond surface and consequently the evolution of the electrostatic potential over the cantilever surface. The approach successfully enabled one to probe variations in cantilevers bending stiffness from several tens to hundreds of millinewtons/meter, thus opening the way for diamond microcantilevers to direct sensing applications in liquids. The evolution of the diamond surface chemistry was also investigated using X-ray photoelectron spectroscopy.

Surface Bio-functionalization of boron doped diamond

Biotin was grafted onto boron doped nanocrystaline diamond electrode through a four-step-chemical process. First step of grafting was electro-chemical reduction of p-4,nitro diazonium salts. The grafting was characterized using X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and fluorescence analysis. XPS analysis and curve fitting procedure lead to the identification of different bond states of carbon present in the grafted film and highlights difference of coverage rate between samples. AFM highlights the non-mononuclear aspect of the diazonium electrografting. Fluorescence measurements with avidin recognition prove the efficient of the grafting.