(Invited) Improved the Impedance Spectroscopy Measurements with Non-Contact Microelectrodes Embedded into a Flexible Polymer Comprising a Microfluidic Network
Authors: Kechadi Mohammed , Tribollet Bernard , Gamby Jean 
Published: February 2020

In the last decade, the flexible microdevices were abundtly developed for microfluidics. Among the electric measurement strategies for sensors or biosensors, the electric impedance spectroscopy on insulated polymer sandwiched between two microelectrodes is promising as new technique for detection strategy because of the absence of direct contact between the microelectrodes and solution flowing in the fluidic microchannel.

Our strategy is based on the capacitive coupling between the microelectrodes galvanically isolated in a dielectric polymer such as polyethylene terephthalate (PET) into which a fluidics microchannel is designed by laser photoablation procedure [1],[2]. In other words, the capacitive coupling takes place between the two planar microband electrodes located on one side of the dielectric polymer and the fluidics microchannel solution in contact with the other side. In brief, the thin dielectric polymer layer (e=5 µm) is sandwiched between the two microelectrodes (electronic charges) and a flow microchannel (ionic charges).

More recently a detailed methodology for non-contact impedance in such dielectric microdevice has been published [3,4] that presents a procedure to eliminate the impedance contribution of the PET layer which separates the two embedded microelectrodes. This procedure enables a clear observation of the impedance of the solution in the microchannel associated in series with the interfacial impedance (PET surface / Solution).

Indeed, eliminating the contribution of the impedance of the polymer enables new applications such as conductometry in the high-frequencies [4]. Conversely, this configuration permits in the low-frequencies the monitoring the interfacial impedance change onto polymer. Indeed, the PET surface charge state depends on the chemical surface modification of the PET.

Some applications and results of the use of the non-contact impedance spectroscopy over a fluidics microchannel will be presented. For instance, the adsorption monitoring of proteins on the polymer surface or the contactless conductivity variation while a chemical reaction takes place in the fluidic channel. Modelling of the interface constituted by PET/microelectrode/electrolyte were investigated using the electrical equivalent circuits approach or using numerical calculations permittingto extract the value of the interfacial impedance for an ultralow protein concentration. The promising results obtained with a detected labelling-free protein represent a competing method with optical instruments using surface plasmon resonance (SPR).

References

[1] J. Gamby, J.-P. Abid and H. H. Girault, J. Am. Chem. Soc.
2005, 127, 13300-13304.

[2] J. Gamby, J. P. Abid, B. Tribollet and H. H. Girault, Small
2008, 4, 802-809.

[3] M. Faure, M. Kechadi, B. Sotta, J. Gamby and B. Tribollet, Electroanalysis
2013, 25, 1151-1158.

[4] M. Kechadi, J. Gamby, L. Chaal, H. Girault, B. Saidani and B. Tribollet, Electrochim. Acta
2013, 105, 7-14.