Naked-Eye Displacement-Induced Off-On-Off Detection of Aluminum and Fluoride in Water

This study examined Rh-TPA, a rhodamine-triphenylamine conjugate functioning as a dual-mode chemosensor, in water. The Rh-TPA exhibits a selective fluorescence "turn-on" response only toward aluminum; however, in co-ion systems, this response is suppressed by fluoride. This observation limits the probe's effectiveness as an aluminum sensor in ion mixtures containing fluoride ions. Therefore, the highlight of this study is that the Rh-TPA-Al³⁺ complex can be used as a selective "turn-off" fluoride sensor. For quick, field-ready use, the Rh-TPA-Al³⁺ complex can be applied to filter paper strips and read with a smartphone camera through simple RGB analysis. Overall, these features make the Rh-TPA-Al³⁺ a practical tool for on-site environmental monitoring of fluoride ion levels.