Fabrication of an electrochemical sensor based on spiropyran for sensitive and selective detection of fluoride ion

In the past decades, numerous electrochemical sensors based on exogenous electroactive substance have been reported. Due to non-specific interaction between the redox mediator and the target, the instability caused by false signal may not be avoided. To address this issue, in this paper, a new electrochemical sensor based on spiropyran skeleton, namely SPOSi, was designed for specific electrochemical response to fluoride ions (F⁻). The breakage of Si–O induced by F⁻ based on the specific nucleophilic substitution reaction between F⁻ and silica would directly produce a hydroquinone structure for electrochemical signal generation. To improve the sensitivity, SPOSi probe was assembled on the single-walled carbon nanotubes (SWCNTs) modified glassy carbon electrode (GCE) through the π–π conjugating interaction. This electrode was successfully applied to monitor F⁻ with a detection limit of 8.3 × 10⁻⁸ M. Compared with the conventional F⁻ ion selected electrode (ISE) which utilized noncovalent interaction, this method displays higher stability and a comparable sensitivity in the urine samples.