Eriochrome Black T–Eu3+ Complex as a Ratiometric Colorimetric and Fluorescent Probe for the Detection of Dipicolinic Acid, a Biomarker of Bacterial Spores

A novel ratiometric colorimetric and fluorescent dual probe based on Eriochrome Black T (EBT)–Eu3+ complex was designed to detect dipicolinic acid (DPA), a major constituent of bacterial spores, with high sensitivity and selectivity. UV–vis titration experiments demonstrated that EBT and Eu3+ ions formed a 1:1 coordination pair in water. In the presence of Eu3+ ions, the blue solution of EBT changed to magenta, however, upon the addition of DPA, the magenta color changed to blue immediately and characteristic fluorescence emission from DPA–Eu3+ complex was observed. In addition, the sensitivity of the system was further evaluated on Geobacillus stearothermophilus spores and as low as 2.5 × 105 spores were detected.