Highly selective "turn-on" fluorescent sensing of fluoride ion based on a conjugated polymer thin film-Fe³⁺ complex

We designed a new fluorescent conjugated polymer thin film sensor via direct electropolymerization of the corresponding electroactive monomer M onto the surface of ITO electrode, and the thin film-Fe³⁺ complex was used for the highly-selective detection of fluoride ion (F^-) in water environmental samples. The as-obtained thin film could effectively detect Fe³⁺ as a selective turn-off fluorescent sensor, and exhibited outstanding reversibility. This film in the presence of Fe³⁺ showed a highly selective turn-on response toward F^- over other anions with a 5-fold enhancement in the fluorescence intensity. F^- with a relatively wide concentration range from 10 μM to 3 mM could be determined in a rather simple and sensitive manner with a detection limit of 6.78 μM (0.128 ppm). Analytical applicability of the film-Fe³⁺ complex for determining the levels of F^- in environmental water samples has been successfully demonstrated by fluorescent analysis with satisfactory results. This strategy will provide a new approach for the facile design of new molecular sensing devices and practical application in environments.