A cationic lanthanide-based fluorescent sensor for highly selective and on-site detection of chromium oxyanions

The detection of Cr(VI) oxyanions in aquatic environments has garnered significant attention due to their biotoxicity, environmental risks, and pivotal role in the nuclear fuel cycle, particularly in environmental and industrial applications. However, existing fluorescent probes for CrO₄²⁻ and Cr₂O₇²⁻ are often constrained by low sensitivity, poor selectivity, and complex detection procedures. In this study, we report the development of a hydrolytically stable cationic lanthanide-based cluster, Tb-bppCOO, which exhibits excellent chemical and photoluminescence stability across a broad pH range (4–10). The intrinsic luminescence of Tb³⁺ facilitates the detection of CrO₄²⁻ and Cr₂O₇²⁻ through a luminescence quenching mechanism, exhibiting a good linear Stern–Volmer relationship (I₀/I = 1 + Ksv [Q]) in the concentration range of 0–80 μM. The quenching effect is attributed to the partial overlap of the absorption peak of Tb-bppCOO with the absorption of Cr(VI) at 365 nm, allowing chromium oxyanions to compete for excitation light upon adsorption, thereby achieving selective detection of CrO₄²⁻ and Cr₂O₇²⁻ with detection limits of 148 nM and 58 nM, respectively. Moreover, integration of Tb-bppCOO into PVDF films demonstrates its potential as a promising material for on-site and semi-quantitative analysis of Cr(VI) oxyanions in aqueous solutions.