Electrochemical Sensor Research at the Laboratoire d'Electrochimie of the EPFL
This review presents some recent developments in the field of electroanalytical sensors. We first explain the working principle of electrochemistry at the interface between two immiscible electrolyte solutions (ITIES), illustrated by the example of copper transferring through a water/1,2-dichloroethane interface when the ionophore 1,4,7,10-tetrathiacyclododecane is present in the organic phase. The obtained results show that assisted ion-transfer reactions take place with both CuI and CuII, but that the interfacial process is complicated by the fact that CuI disproportionates in water and that CuII can be reduced in the organic phase.
Based on the same experimental methodology, a new type of amperometric detector for non-redox ions has been developed using a composite polymer membrane supporting a gelified organic phase that can incorporate an ionophore such as valinomycin. We report here the use of a (o-nitrophenyloctylether)-(poy(vinyl chloride) (NPOE-PVC) gel micro-interface as a detector for cations and anions in ion-exchange chromatography. The main advantage of this approach is that selectivity and sensitivity can be tailored by the choice of the ionophore and by the polarisation potential.
This ion detector has also been incorporated in a miniaturised total-analysis system (µ-TAS) fabricated in a polymer sheet by UV-laser photoablation. This microfabrication technique is used for the prototyping of a disposable capillary-electrophoresis microsystem comprising on-chip injector, separation column and electrochemical detector. This system is further used with built-in carbon-ink electrodes for the detection of electroactive species. These microsystems are now under development for immuno-sensor applications.
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