The role of l-histidine as molecular tongs: a strategy of grasping Tb 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 , was constructed by coordination of Tb 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 firmly to form a stable lanthanide-doped nanoparticle (His@ZIF-8/Tb). Owing to the unsaturated coordination of Tb with the amino acid group, the resultant His@ZIF-8/Tb showed reserved response sites of Tb to DPA because of its unique molecular structure. After the His@ZIF-8/Tb coordination with DPA, the intrinsic fluorescence emission of the Tb 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 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 ( = 0.999) ranging from 0.08 to 10 μmol L and an ultralow limit of detection (LOD) of 0.02 μmol L. This strategy for the design of functionalized MOFs to construct sensing probes and the resultant His@ZIF-8/Tb 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.