Ratiometric fluorescence detection of 2,6-pyridine dicarboxylic acid with a dual-emitting lanthanide metal-organic framework (MOF)

Bacillus anthracis is an extremely dangerous bacterium with high morbidity and mortality. It is thus of great importance to detect Bacillus anthracis or its major biomarker 2,6-pyridine dicarboxylic acid (DPA) in a rapid and sensitive way. Althought metal-organic frameworks (MOFs) have found great applications in catalysis and sensing; nevertheless, there are only a few fluorescent MOFs can be used in DAP detections, and the key factors determining the detection sensitivity is not clear yet. In this study, we successfully synthesized a novel nano-sized dual-emitting lanthanide MOF, namely Eu/Tb(BTC), for the high-sensitivity DPA detection. The synthesized Eu/Tb(BTC) showed a remarkable sensitivity, excellent selectivity, and a high accuracy. Through comprehensive characterizations of the microstructure, luminescence properties, and sensing performance of products with different Eu/Tb ratios, the unique capability as a sensitive fluorescent probe (limit of detection 1087 nM) for selectively detecting DPA was demonstrated. More importantly, a possible route to control the sensitivity of detection by controlling the original energy transfer efficiency between Eu3+ and Tb3+ was revealed. This work not only provides an excellent nano-probe for qualitative and quantitative detection of biomarker of Bacillus anthracis, but also reveals an important rule for improving the sensitivity of sensing systems.