A visible BODIPY-based sensor for 'Naked-Eye' recognition of Ag⁺ and its application on test paper strips

In this study, a novel, highly sensitive fluorescent sensor (E)-2-((2-(benzo[d] thiazol-2-yl) quinolin-8-yl) oxy)-N'-(4-(5, 5-difluoro-1, 3, 7, 9-tetramethyl-5H-4λ⁴, 5λ⁴-dipyrrolo [1, 2-c:2', 1'-f] [1, 3, 2] diazaborinin-10-yl) benzylidene) acetohydrazide (TQB) was developed for dual mode of Ag⁺ detection (colorimetric/fluorescence), and its structural and spectral properties were characterized by ¹H NMR, ESI-MS, X-ray, ultraviolet and fluorescence photometry. It is found that TQB could specifically and efficiently identify Ag⁺ among many other metal ions in CH₃OH/H₂O (7:3 v/v, pH = 7.23) buffer. The maximum absorption wavelength of TQB is red-shifted while its fluorescence is quenched with a quenching rate of 88.7%. The energy difference between TQB and TQB-Ag⁺ complex was calculated by DFT, and the applicability of TQB was verified by paper strip test. In addition, TQB has been successfully applied to the determination of Ag⁺ in real water samples with good reversibility and recoveries.