Gold nanocluster-europium(III) ratiometric fluorescence assay for dipicolinic acid

A ratiometric fluorescence assay was designed for determination of dipicolinic acid (DPA), a spore-specific compound which is used as a biomarker for Bacillus anthracis spores for food and medical product safety analysis. The dual-channel fluorescence probe integrates two fluorescent materials, Eu³⁺ ion and gold nanocluster (Au NC). The Au NC is used as a reference channel to measure background noise and the Eu³⁺ ion as the DPA-specific response signal channel. The probe was prepared through simply combing bovine serum albumin (BSA)-scaffolded Eu³⁺ ion and Au NCs. When excited at 530 nm, in the presence of DPA, the fluorescence signals of Eu³⁺ ion at 595, 617, and 695 nm increased significantly while the 650 nm signal of Au NC reference remained relatively constant. This fluorescence probe has good photo-stability and also displays good selectivity and high sensitivity for DPA with a low detection limit of 0.8 μM. The linear range of the ratiometric probe for DPA is 1-50 μM. For determination of DPA released during the germination of Bacillus subtilis spores, the detection results were in agreement with measurements by conventional calorimetry assay. The method may have potential for measuring the level of contamination and germination by spores. Graphical Abstract Dual-channel fluorescence biosensor was designed to detect dipicolinic acid, a spore-specific compound which is used as a biomarker for Bacillus anthracis spores for food and medical product safety analysis.