Fanny Hauquier

Conducting Ferrocene Monolayers on Nonconducting Surfaces

The redox activity of a ferrocenyl monolayer grafted on an n-type Si111 substrate was investigated by scanning electrochemical microscopy (SECM) in conditions where the substrate plays the role of an insulator. This approach permits the differentiation between the different possible electron-transfer and mass-transport pathways occurring at the interface. As an exciting result, the thin ferrocenyl monolayer behaves like a purely conducting material, highlighting very fast electron communication between immobilized ferrocenyl headgroups in a 2D-like charge-transport mechanism.

Scanning Electron Microscopy Investigation of Molecular Transport and Reactivity within Polymer Brushes

Scanning electrochemical microscopy (SECM) allows investigation of the transport of redox probes within polymer brushes grown by atom-transfer radical polymerization (ATRP) from gold electrodes. By combination with cyclic voltammetry, the permeation of aqueous or organic redox probes is described and quantified in poly(glycidyl methacrylate) (PGMA) and polystyrene (PS). It is related to the chemical nature of both the probe and its environment (the solvent and the polymer phases). This study anticipates the permeation of reactive species within polymer brushes for further etching. The SECM reductive etching of the terminal C-Br bond of PGMA or PS macroinitiator layers is then investigated for different polymer thicknesses. The incomplete reductive etching of the macroinitiator layers is in agreement with the low permeability of the etchant within such polymer brushes and with the distribution of the terminal C-Br bonds throughout the brush. SECM proves to be a convenient tool for patterning such macroinitiator surfaces to form channels in block-copolymer structures. The combination of both analytical and patterning investigations enables one to anticipate and understand the reactivity of grafted macromolecules.

Oxidative and stepwise grafting of dopamine inner-sphere redox couple onto electrode material: electron transfer activation of dopamine.

The immobilization of dopamine, a neurotransmitter, onto macroelectrode and microelectrode surfaces has been performed following two strategies. The first consists of a one-step grafting based on electrochemical oxidation of an amino group in acidic media. The second is a stepwise process starting with electrochemical grafting of diazonium, leading to the attachment of aryl layer bearing an acidic headgroup, followed by chemical coupling leading to immobilized dopamine molecules onto the electrode surface. Electrochemical, infrared (IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses evidence that both methods are suitable for the immobilization of dopamine onto millimetric and micronic electrodes. The electrochemical responses of modified electrodes demonstrate that the electroactivity of the attached dopamine layer appears unaffected by the nature of the spacer, alkyl or aryl layers, suggesting that the communication, through tunneling, between the attached dopamine and the electrode is possible. More interestingly, the dopamine-modified electrode exhibits electron transfer activation toward dopamine in solution. As a result, not only does the dopamine modified electrode yield a fast electron transfer with lower ΔE(p) (30 mV) than the majority of pretreatment procedures but also the ΔE(p) is as small as that observed for more complex surface treatments.

Redox-active organic monolayers deposited on silicon surfaces for the fabrication of molecular scale devices

Different Si(111) surfaces covalently derivatised with alkyl monolayers terminated by redox-active centres, namely reversibly oxidisable ferrocene and tetrathiafulvalene (TTF), and electrochemically polymerisable pyrrole, have been prepared. Ferrocene and pyrrole were attached to the silicon surface using carbodiimide coupling between an amino-substituted derivative and a pre-assembled acid-terminated monolayer. TTF monolayers were produced from the direct reaction of an alcohol-substituted TTF derivative with hydrogen-terminated Si(111). The electrochemical oxidation of the pyrrole-modified surface in the presence of pyrrole yielded strongly adherent and smooth conducting polypyrrole films, the thickness of which could be easily controlled from the consumed electrical charge. The hybrid polypyrrole/pyrrole monolayer/Si(111) junction showed the expected metal-insulator-semiconductor (MIS) diode behaviour with a rectification factor at ?2 V of ca. 280. The electrochemical characteristics of the ferrocene- and TTF-modified surfaces evidenced a single and two one-electron system(s) respectively, located at potentials very close to those observed with the electroactive compounds in solution. The surface coverages of ferrocene and TTF were 0.23 and 0.15 per surface silicon atom respectively. Moreover, the rate constants of electron transfer were found to be 50 s−1 and 25 s−1 for the ferrocene and TTF monolayers respectively.

Carbon nanotube-functionalized silicon surfaces with efficient redox communication

Sidewall functionalized multi-walled carbon nanotubes can be covalently bound parallel to a silicon surface via a self-assembled acid-terminated monolayer used as an organic molecular glue.

Validation of a simple HPLC-UV method for rifampicin determination in plasma: Application to the study of rifampicin arteriovenous concentration gradient

In clinical practice, rifampicin exposure is estimated from its concentration in venous blood samples. In this study, we hypothesized that differences in rifampicin concentration may exist between arterial and venous plasma. An HPLC-UV method for determining rifampicin concentration in plasma using rifapentine as an internal standard was validated. The method, which requires a simple protein precipitation procedure as sample preparation, was performed to compare venous and arterial plasma kinetics after a single therapeutic dose of rifampicin (8.6 mg/kg i.v, infused over 30 min) in baboons (n=3). The method was linear from 0.1 to 40 μg mL(-1) and all validation parameters fulfilled the international requirements. In baboons, rifampicin concentration in arterial plasma was higher than in venous plasma. Arterial Cmax was 2.1±0.2 fold higher than venous Cmax. The area under the curve (AUC) from 0 to 120 min was ∼80% higher in arterial plasma, indicating a significant arteriovenous concentration gradient in early rifampicin pharmacokinetics. Arterial and venous plasma concentrations obtained 6h after rifampicin injection were not different. An important arteriovenous equilibration delay for rifampicin pharmacokinetics is reported. Determination in venous plasma concentrations may considerably underestimate rifampicin exposure to organs during the distribution phase.

Graphene Films for Corrosion Protection of Gold Coated Cuprous Substrates in View of an Application to Electrical Contacts

Corrosion of gold coated electrical contacts remains a problem often avoided by keeping the final gold coating thicknesses over 1 μm. Graphene has recently been shown to be an outstanding material: among its astonishing properties are the theoretical carrier mobility at room temperature (200 000 cm2/V-1s-1) and the Young modulus (1.5 TPa). Graphene is a one-atom thick two-dimensional carbon crystal and has been first produced by mechanical exfoliation to obtain high purity defect free sheets. Chemical vapour deposition (CVD) is another method producing larger areas of graphene. Much work has been dedicated to graphene oxide (GO) deposition and reduction processes for applications ranging from electronics to sensors. In this work we describe briefly how a method of liquid exfoliation and spray deposition can be used to produce nanometric films of graphene flakes which can be more or less uniform and continuous according to the tuning of the process. Films were sprayed in different conditions on various substrates: laboratory substrates such as evaporated gold on glass, Si wafers and metallic coupons. The coupons under study were cut from cuprous alloy strips with a 2μm Ni underlayer and a 0.8 μm Au layer. The coupons were coated with graphene films; they were then submitted to a four gas corrosion environmental test of the GR-1217-CORE Nov. 1995 type. A significant protection effect was observed for the sprayed graphene films. The deposition method by means of a spraying device was difficult to characterise but Raman spectroscopy and SEM images of the sprayed films showed evidence of the film formation. Contact resistance measurements and friction tests in a ball plane configuration were performed; low values of resistance and very low friction coefficients were measured. These first results show the very strong potential of graphene films deposited by a spraying method for electrical contacts applications and particularly for corrosion protection.

Multifunctional Indium Tin Oxide Electrode Generated by Unusual Surface Modification

The indium tin oxide (ITO) material has been widely used in various scientific fields and has been successfully implemented in several devices. Herein, the electrochemical reduction of ITO electrode in an organic electrolytic solution containing alkali metal, NaI, or redox molecule, N-(ferrocenylmethyl) imidazolium iodide, was investigated. The reduced ITO surfaces were investigated by X-ray photoelectron spectroscopy and grazing incident XRD demonstrating the presence of the electrolyte cation inside the material. Reversibility of this process after re-oxidation was evidenced by XPS. Using a redox molecule based ionic liquid as supporting electrolyte leads to fellow electrochemically the intercalation process. As a result, modified ITO containing ferrocenyl imidazolium was easily generated. This reduction process occurs at mild reducing potential around −1.8 V and causes for higher reducing potential a drastic morphological change accompanied with a decrease of the electrode conductivity at the macroscopic scale. Finally, the self-reducing power of the reduced ITO phase was used to initiate the spontaneous reduction of silver ions leading to the growth of Ag nanoparticles. As a result, transparent and multifunctional active ITO surfaces were generated bearing redox active molecules inside the material and Ag nanoparticles onto the surface.

Boronic Acid-Functionalized Oxide-Free Silicon Surfaces for the Electrochemical Sensing of Dopamine

Boronic acid monolayers covalently bound to hydrogen-terminated Si(111) surfaces have been prepared from the UV-directed hydrosilylation reaction of 4-vinylbenzeneboronic acid. X-ray photoelectron spectroscopy (XPS) analysis of the modified surface revealed characteristic peaks from the attached organic molecule with the expected molecular composition and without the oxidation of underlying silicon. From XPS data, the surface coverage was estimated to be ca. 0.34 ± 0.04 ethylbenzene boronic acid chain per surface silicon atom (i.e., (4.4 ± 0.5) × 10-10 mol cm-2), which is consistent with a densely packed monolayer. The electrochemical impedance spectroscopy measurements performed at pH 7.4 in the presence of the Fe(CN)63-/Fe(CN)64- reporter couple showed specific dopamine-induced changes as a result of the binding of the guest molecule to the immobilized boronate species. The charge-transfer resistance (Rct) was found to decrease from 4.9 MΩ to 14 kΩ upon increasing the dopamine concentration in the range of 10 μM-1 mM. Furthermore, the presence of the interfering ascorbic acid until a concentration of 10 mM did not significantly change the electrochemical response of the functionalized surface. Comparative electrochemical data obtained at the reference ethylbenzene monolayer provided clear evidence that the immobilized boronic acid units were responsible for the observed changes.

Anodic behaviour of methylidene-cyclopentadiaryl derivatives: cyclic voltammetry and theoretical study

Electrochemical behaviour of a functionalized fluorenylidene 1 is studied in comparison with a cyclopentadithiophene analogue 2. The influence of the main aromatic group on the electropolymerization ability is reported. We demonstrated that the lack of sulfur atoms in the monomer structure leads to an absence of polymerization due to the spin density located on the methylidene bridge in the radical cation. From modelling considerations, we have evaluated the participation of the methylidene bridge in the p-doping process. The good correlation between the p-doping level and the partial atomic charge carried by the methylidene bridge for poly(2) and poly(3) indicates that an extension of the conjugated area improves the p-doping level when the side chain is electronically connected to the main chain of polymer.