Dual-Response Visual Fluorescent Probes for the Determination of Vanadate and Morphology over a Wide pH Range

Vanadate has become an important indicator for environmental testing due to its high toxicity, mobility, and difficulty in degradation. In addition, depending on its dynamic aggregation, analyzing vanadate is not a single content test; it needs further morphological analysis. Previous research has tended to construct a single functional platform with complicated procedures and expensive equipment, making it difficult to obtain a comprehensive picture of vanadate in a short time. Herein, we constructed a dual-response fluorescent probe EuTAT@Rh B formed by Eu³⁺, 2-aminoterephthalic acid (TAT), and rhodamine B, which could generate structural changes based on the morphology distribution characteristics of vanadate with pH. In the concentration range from 5 × 10^-7 to 2 × 10^-4 mol/L, the detection limits (3σ/slope, σ = <i>s</i>/<i>I</i>₀) of orthovanadate VO₄^3- and metavanadate VO₃^- were 1.67 × 10^-8 and 2.0 × 10^-9 mol/L, respectively. In addition, under 254 nm UV light, the spirolactam ring-controlled structures varied with pH and vanadate concentration, producing different types of photochromic structures, which were able to correspond essentially to the pH range of vanadate morphology distribution. Thus, a window with both vanadate and pH signals was constructed under the dual channels of UV and fluorescence, and we successfully achieved the visual integrated analysis of vanadate. This dual-channel visualization method has the advantages of simplifying the analysis process and improving the detection efficiency, which is of great significance in practical applications and provides a way to identify other polymeric substances.