Lila Chaal

A real time affinity biosensor on an insulated polymer using electric impedance spectroscopy in dielectric microchips.

This paper presents development of real time monitoring of binding events on flexible plastic in microchips. Two planar carbon microelectrodes are integrated into an insulated polyethylene terephthalate microchip without direct electrical contact with the solution in the microchannel. It has been possible to probe the electric impedance changes through the interface constituted by the microelectrode/PET microchannel/solution when a biomolecular interaction takes place on the polymer surface. This new transduction for biosensing was demonstrated for the molecular recognition of BSA immobilized on the polymer microchannel surface using the corresponding rabbit anti-BSA antibodies as an analyte in the flow microchannel at the nanomolar range concentration. The equilibrium association constant was determined for the affinity reaction between both ligands and was obtained equal to 5 × 10(7) M(-1). The promising results obtained with this new device make it a competitive biosensor.

Free Contact Microchannel Impedance Through Two Antiparallel Planar Microelectrodes

The present work describes new results using a contact free impedance device, which permits to reach a best understanding of the free contact transduction. Measurements were carried out through a polyethylene terephthalate (PET) microchannel photoablated. Impedance measurement of empty microchannel at different PET thickness separating the two electrodes demonstrate that the recorded impedance is not changed whatever the PET thickness. The result shows that the polyethylene (PE) film lamination has an effect on the impedance measurement in empty microchannel. Then impedances diagrams in the filled microchannel were plotted by subtracting impedance contribution in empty microchannel from the global microdevice response. The Nyquist diagram of filled microchannel exhibits a loop diameter from high to medium frequencies, and a capacitive behavior at low frequencies. The loop diameter obtained is inversely proportional to the microchannel conductivity. Modeling impedance of microsystem highlighted the effect of microchannel rough surface phenomena.

Structural, Viscoelastic, and Electrochemical Characteristics of Self-Assembled Amphiphilic Comblike Copolymers in Aqueous Solutions

Self-assembly in aqueous solutions of an amphiphilic comblike polyelectrolyte (80C12) that consists of a polystyrene (PS) backbone onto which quaternary ammonium pendant moieties have been grafted has been investigated by light scattering and cryo-transmission electron microscopy measurements in the presence of KCl and methylviologen dication (MV2+) under conditions mimicking those for electrochemical measurements. Polymer chains self-assemble within branched cylindrical micelles that display viscoelastic properties, characterized by a relaxation time of 4 s. To tune this time, 80C12 was mixed with a polyoxyethylene nonionic surfactant (Brij C12E10). Relatively increasing the amount of the latter leads to a decrease in the relaxation time of the 80C12 solution. Correlatively, electrochemical experiments with a rotating disk electrode show a transition of the mass transport rate, which deviates from the classical Newtonian behavior in the same velocity domain. This result generalizes what has been already observed with solutions of linear polymers of high molecular weight and wormlike micelles based on surfactants subjected to elongational deformations. Moreover, the critical times derived from rheological and electrochemical experiments display the same trend.