A switchable electrochemical redox ratiometric substrate based on ferrocene for highly selective and sensitive fluoride detection

A novel latent electrochemical probe based on a ferrocenyl carbamate derivate (FCCD) was synthesized for the highly selective ratiometric detection of fluoride (F-). FCCD was synthesized through an easy, one step reaction using ferrocenyl azide and silyl protected benzyl alcohol as precursors through a Curtius rearrangement. In presence of F-, FCCD undergoes a nucleophilic substitution reaction, which led to the removal of silyl protecting group through 1,6-quinone-methide rearrangement with concomitant release of ferrocenyl amine (FA). As the concentration of F- increases, the amount of FCCD is dissipated, while that of FA accumulated in the reaction medium were monitored through the linear changes in their redox couples. Compared with a conventional ion selective electrode, the use of a cheaper unmodified electrode as a transducer coupled with FCCD displayed higher stability, excellent selectivity and better sensitivity with LOD of 5.1 × 10-7 M (9.69 ppb). Moreover, FCCD is a selective and sensitive colorimetric visualization probe for F-. The proof-of-concept of the approach is demonstrated in direct toothpaste sample (non-transparent solutions), biological and water samples. The important advantages of this approach are high selectivity, the use of cheaper unmodified electrode, adoption of simple electrochemical methods, dual channel detection, low overpotential of the reporter, naked-eye detection, and ability to detect F- in non-transparent samples.