Theory and Experiments of Transport at Channel Microband Electrodes under Laminar Flows. 3. Electrochemical Detection at Electrode Arrays Under steady state.
C. Amatore, N. Da Mota, C. Sella, L. Thouin, Anal. Chem. in press. (Abstract + PDF)

Microband arrays improve the analytical performances and the information contents of the electrochemical detection in flow channel relative to single-electrode configurations. However, exploiting their full advantages requires a detailed understanding of the properties of arrays, which depend on their geometry and on the hydrodynamic regimes established inside the microfluidic channel. This paper investigates the influence of two main operating situations (sequential and coupling regimes) on steady-state amperometric responses of microband arrays performing under laminar flow conditions. Simulations and experimental measurements showed that the resulting properties of the arrays are a function of the number of electrodes and average ratio between gaps and electrode widths, whether the layout of the arrays is regular or not. Since the contribution of each electrode can be finely tailored, this allows the arrays to be designed and adapted to a wide variety of experimental demands.

Finding Out Egyptian Gods' Secret Using Analytical Chemistry: Biomedical Properties of Egyptian Black Makeup Revealed by Amperometry at Single Cells.
I. Tapsoba, S. Arbault, P. Walter, C. Amatore, Anal. Chem., 82, 2010, 457-460.

Lead-based compounds were used during antiquity as both pigments and medicines in theformulation of makeup materials. Chemical analysis of cosmetics samples, found in Egyptians tombs and the reconstitution of ancient recipes as reported by Greco-Roman authors have shown that two non-natural lead chlorides (laurionite Pb(OH)Cl and phosgenite Pb2Cl2CO3) were purposely synthesized and were used as fine powders in makeup and eye lotions. According to ancient Egyptian manuscripts, these were essential remedies for treating eye illness and skin ailments. This conclusion seems amazing because toddy we focus only on the well-recognized toxicity of lead salts. Here, using ultramicroelectrodes, we obtain new insights into the biochemical interactions between lead(II) ions and cells, which support the ancient medical use of sparingly soluble lead compounds. Submicromolar concentrations of Pb2+ ions are shown to be sufficient for eliciting specific oxidative stress responses of keratinocytes. These consist essentially of an overproduction of nitrogen monoxide (NO degrees). Owing to the biological role of NO degrees in stimulating nonspecific immunological defenses, one may argue that these lead compounds were deliberately manufactured and used in ancient Egyptian formulations to prevent and treat eye illnesses by promoting the action of immune cells.

Cyclic Voltammetry at Microelectrodes. Influence of Natural Convection on Diffusion Layers as Characterized by in-situ Mapping of Concentration Profiles.
C. Amatore, C. Pebay, L. Thouin, A. Wang, Electrochem. Commun. 11, 2009, 1269–1272. (Abstract + PDF)

Cyclic voltammetry was performed at microelectrodes under experimental conditions where no forced convection participates to the mass transport. Mapping of the dynamic concentration profiles were achieved using a method previously described. According to the time scale of the experiments and size of the microelectrodes, the results show that several regimes may be achieved. To delineate respectively the involvement of planar diffusion, hemispherical diffusion and natural convection in the overall mass transport, the experimental voltammograms and concentration profiles were compared to simulated ones accounting for each contribution. Excellent agreement was observed between data and predictions establishing that convection influences cyclic voltammetry even at microelectrodes reputed to be immune owing to their micrometric sizes.

Invariance of Exocytotic Events Detected by Amperometry as a Function of the Carbon Fiber Microelectrode Diameter.
C. Amatore, S. Arbault, Y. Bouret, M. Guille, F. Lemaître, Y. Verchier, Anal. Chem., 81, 2009, 3087-3093.

Etched carbon fiber microelectrodes of different radii have been used for amperometric measurements of single exocytotic events occurring at adrenal chromaffin cells. Frequency, kinetic, and quantitative information on exocytosis provided by amperometric spikes were analyzed as a function of the surface area of the microelectrodes. Interestingly, the percentage of spikes with foot (as well as their own characteristics), a category revealing the existence of sufficient long-lasting fusion pores, was found to be constant whatever the microelectrode diameter was, whereas the probability of overlapping spikes decreased with the electrode size. This confirmed that the prespike foot could not feature accidental superimposition of separated events occurring at different places. Moreover, the features of amperometric spikes investigated here (charge, intensity and kinetics) were found constant for all microelectrode diameters. This demonstrated that the electrochemical measurement does not introduce significant bias onto the kinetics and thermodynamics of release during individual exocytotic events. All in all, this work evidences that information on exocytosis amperometrically recorded with the usual 7 µm diameter carbon fiber electrodes is biologically relevant, although the frequent overlap between spikes requires a censorship of the data during the analytical treatment.