To avoid water competition in indicator-displacement assays (IDA), encapsulation of the receptor into a polymer film or behind a water-impermeable polymeric membrane are methods that have been generally investigated. The new results obtained by Jean-Marc Vincent and his colleagues from the Institut des Sciences Moléculaires in Bordeaux, France, show that the use of a fluorous phase should now be considered as a possible alternative.

Vincent's group first reported in 2002 preliminary results on reversible phase-switching of pyridyl-tagged compounds between hydrocarbon and perfluorocarbon (PFC) phases. The growing interest on ethanol as an energy source naturally attracted the Bordeaux team's attention, and the French chemists hypothesised that their methodology could be employed to develop a "simple" colorimetric assay for ethanol detection and/or titration. In this work Vincent et al. clearly demonstrated that compartmentalization of a chemosensing ensemble in a PFC may allow its use in conjunction with an aqueous phase (containing the analyte) without interference due to interactions with water (Scheme 1). 

Scheme 1Principle of the compartmentalised fluorous IDA.

The simple fact that ethanol can be selectively detected in a vast amount of water, whilst ethanol and water should exhibit similar coordinating properties towards copper(II) ions, is a significant result.   

A major drawback of the present ethanol assay remains in the use of chloroform, a toxic chlorinated solvent as a detection phase. To counter this problem, the authors are now employing their efforts to develop water-soluble indicators.