An effective electrochemical sensing platform for fluoride ions based on fluorescein isothiocyanate–MWCNT composite?

New Journal of Chemistry Pub Date: 2018-05-23 DOI: 10.1039/C8NJ01703D

Abstract

Fluorogenic F? sensors based on fluorescein isothiocyanate (FITC-OSi) are highly selective because they rely on reactions between silica and F?. However, the low intrinsic fluorescence quantum yield of FITC-OSi and the susceptibility of fluorescent signals to be changed by factors other than F? concentration have limited their practical use. Herein, we show that the intrinsic redox properties of FITC-OSi can be used instead of its fluorescence as the transducing signal to overcome these challenges. FITC-OSi and pristine multiwalled carbon nanotubes (p-MWCNTs) were assembled on GCEs to form FITC-OSi–p-MWCNT–GCE electrodes. Cyclic voltammetry was used to analyse its current response in the presence of F? using an experimental design that mimicked the operation of a screen-printed electrode. The electrode generates two anodic current signals at different potentials with F? addition due to the oxidation of FITC phenolates formed during the reactions of silica and F?. This reaction is irreversible and diffusion controlled. The anodic current is proportional to the amount of F? in solution and a maximum RSD of 5% was recorded after repeated experiments. This showed the stability of the electrode and reproducibility of its current response. p-MWCNTs were used to tune the charge transfer properties of the electrode and allow the anodic current to be detected. The method used to incorporate p-MWCNTs into the electrode and their loading significantly affected the current response of the electrode. The electrode worked well in tap water and showed high selectivity, sensitivity, and a low detection limit of 0.26 μM, which was lower than the drinking water standard set by the EPA and WHO. This work shows that reliable and robust F? sensing electrodes based on fluorogenic sensors can be prepared, which opens the door for applications in new technologies, such as screen-printed electrodes.

Graphical abstract: An effective electrochemical sensing platform for fluoride ions based on fluorescein isothiocyanate–MWCNT composite
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