Dual-Response\nVisual Fluorescent Probes for the Determination\nof Vanadate and Morphology over a Wide pH Range

Vanadate has become an important indicator for environmental\ntesting\ndue to its high toxicity, mobility, and difficulty in degradation.\nIn addition, depending on its dynamic aggregation, analyzing vanadate\nis not a single content test; it needs further morphological analysis.\nPrevious research has tended to construct a single functional platform\nwith complicated procedures and expensive equipment, making it difficult\nto obtain a comprehensive picture of vanadate in a short time. Herein,\nwe constructed a dual-response fluorescent probe EuTAT@Rh B formed\nby Eu<sup>3+</sup>, 2-aminoterephthalic acid (TAT), and rhodamine\nB, which could generate structural changes based on the morphology\ndistribution characteristics of vanadate with pH. In the concentration\nrange from 5 × 10<sup>–7</sup> to 2 × 10<sup>–4</sup> mol/L, the detection limits (3σ/slope, σ = <i>s</i>/<i>I</i><sub>0</sub>) of orthovanadate VO<sub>4</sub><sup>3–</sup> and metavanadate VO<sub>3</sub><sup>–</sup> were 1.67 × 10<sup>–8</sup> and 2.0 × 10<sup>–9</sup> mol/L, respectively. In addition, under 254 nm UV light, the spirolactam\nring-controlled structures varied with pH and vanadate concentration,\nproducing different types of photochromic structures, which were able\nto correspond essentially to the pH range of vanadate morphology distribution.\nThus, a window with both vanadate and pH signals was constructed under\nthe dual channels of UV and fluorescence, and we successfully achieved\nthe visual integrated analysis of vanadate. This dual-channel visualization\nmethod has the advantages of simplifying the analysis process and\nimproving the detection efficiency, which is of great significance\nin practical applications and provides a way to identify other polymeric\nsubstances.