Ratiometric fluorescence determination of the anthrax biomarker 2,6-dipicolinic acid using a Eu3+/Tb3+-doped nickel coordination polymer

Abstract

Tb³⁺/Eu³⁺@Ni-BTC (H₃BTC = 1,3,5-benzenetricarboxylic acid) composites were prepared by soaking the Ni-BTC parent framework in Tb³⁺ and Eu³⁺ ethanol solutions. Various factors were optimized, with the ratio of Tb³⁺ : Eu³⁺at 6 : 4, the soaking time being 30 h, and the MOF dosage being 100 μg. The sensitivity tests of DPA detection by the optimized Tb³⁺_0.6/Eu³⁺_0.4@Ni-BTC indicated a linear relationship of I₅₄₅/I₆₁₃ = 1.24098·C_DPA + 3.80396 where C_DPA = 2–20 μmol L⁻¹, and the limit of detection was calculated as 14.7 nM. Tb³⁺_0.6/Eu³⁺_0.4@Ni-BTC exhibited high selectivity without interference from seven interferents. The detection mechanism is inferred as that DPA sensitizes Tb³⁺ and transfers energy to Eu³⁺, however it blocks the energy transfer from HBTC²⁻ to Eu³⁺. Tb³⁺_0.6/Eu³⁺_0.4@Ni-BTC can be regarded as a potential candidate for a quantitative ratiometric fluorescence sensor for DPA detection with high sensitivity and selectivity.