A double‐barreled approach: The addition of ferrocene to an antiestrogen drug skeleton was found to induce cytotoxicity towards breast‐cancer cells that are resistant to the common antiestrogen drug. The efficacy of this drug has been related to the proton‐coupled electron transfer observed in the presence of pyridine as a base (see picture).

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Integration of microelectrodes in microfluidic devices has attracted significant attention during the past years, in particular for analytical detections performed by direct or indirect electrochemical techniques. In contrast there is a lack of general theoretical treatments of the difficult diffusion-convection problems which are borne by such devices. In this context, we investigated the influence of the confining effect and hydrodynamic conditions on the steady-state amperometric responses monitored at a microband electrode embedded within a microchannel. Several convective-diffusive mass transport regimes were thus identified under laminar flow on the basis of numerical simulations performed as a function of geometrical and hydrodynamic parameters. A rationalization of these results has been proposed by establishing a zone diagram describing all the limiting and intermediate regimes. Concentration profiles generated by the electrode across the microchannel section were also simulated according to the experimental conditions. Their investigation allowed us to evaluate the thickness of the diffusive-convective layer probed by the electrode as well as the distance downstream from which the solution becomes again homogeneous across the whole microchannel section. Experimental checks of the theoretical principles delineated here have validated the present results. Experiments were performed at microband electrodes integrated in microchannels with aqueous solutions of ferrocene methanol under pressure-driven flow.

Using an ultramicroelectrode placed inside the diffusion layer of a larger working electrode we demonstrated to which extent amperometric and potentiometric detections allow spatially resolved information at the micrometric scale, so that the composition of a diffusion layer created in the vicinity of a millimetric working electrode can be examined with adequate precision. The validity of both methods was established experimentally in steady state conditions through the investigation of a simple redox reaction as well as for more complex mechanistic situations. The amperometric detection is also used to probe a time‐expanding diffusion layer, thus showing the transition from perfect Cottrellian behavior to steady state imposed by spontaneous convection.

The development of any particular analytical or preparative applications using electrochemical techniques in microfluidic devices requires integration of microelectrodes. This involves detailed predictions for optimizing the design of devices and selecting the best hydrodynamic conditions. For

Gekoppelte Wirkung: Durch das Anfügen von Ferrocen an das Gerüst eines Antiöstrogenwirkstoffs ließ sich Cytotoxizität gegen Brustkrebszellen induzieren, die gegen den gängigen Antiöstrogenwirkstoff resistent sind. Als Erklärung für die Wirksamkeit dieser Substanz wird der protonengekoppelte Elektronentransfer in Gegenwart der Base Pyridin herangezogen (siehe Bild).

Natural convection in macroscopically immobile solutions may still alter electrochemical experiments performed with electrodes of micrometric dimensions. A model accounting for the influence of natural convection allowed delineating conditions under which it interferes with mass transport. Several electrochemical behaviors may be observed according to the time scale of the experiment, electrode dimensions, and intensity of natural convection. The range of parameters in which ultramicroelectrodes behave under a true diffusional steady state was identified. Mapping of concentration profiles was performed experimentally by scanning electrochemical microscopy in the vicinity of microelectrodes of various radii. The results validated remarkably the predictions of the model, evidencing in particular the alteration of the diffusional steady state by natural convection.

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