The role of l-histidine as molecular tongs: a strategy of grasping Tb(3+) using ZIF-8 to design sensors for monitoring an anthrax biomarker on-the-spot

In this study, a novel lanthanide-doped nanoprobe for monitoring dipicolinic acid (DPA), a unique biomarker of Bacillus anthracis, was constructed by coordination of Tb(3+) with l-histidine (His) functionalized ZIF-8 (His@ZIF-8). After being functionalized with His, the resultant His@ZIF-8 had abundant carboxyl and amino groups, which like tongs help His@ZIF-8 “grasp” Tb(3+) firmly to form a stable lanthanide-doped nanoparticle (His@ZIF-8/Tb(3+)). Owing to the unsaturated coordination of Tb(3+) with the amino acid group, the resultant His@ZIF-8/Tb(3+) showed reserved response sites of Tb(3+) to DPA because of its unique molecular structure. After the His@ZIF-8/Tb(3+) coordination with DPA, the intrinsic fluorescence emission of the Tb(3+) ions was triggered through energy transfer, leading to bright yellow green luminescence owing to the antenna role of DPA. Benefitting from the His functionalization and the characteristics of ZIF-8, especially the high porosity and large surface area, the developed His@ZIF-8/Tb(3+) sensing platform exhibited attractive features as a fluorescent sensor for monitoring DPA such as fast response kinetics (10 s), high sensitivity and selectivity, and being portable, easy to operate, economical and secure. This sensor platform showed a satisfactory linear relationship (R(2) = 0.999) ranging from 0.08 to 10 μmol L(−1) and an ultralow limit of detection (LOD) of 0.02 μmol L(−1). This strategy for the design of functionalized MOFs to construct sensing probes and the resultant His@ZIF-8/Tb(3+) would provide a potential strategy for the exploitation of other functionalized materials used in other research fields and promising fluorescence platforms for the detection of other targets.