A ratiometric fluorescent sensor made of a terbium coordination polymer for the anthrax biomarker 2,6-dipicolinic acid with on-site detection assisted by a smartphone app

2,6-Dipicolinic acid (DPA) is the biomarker of anthrax spores, whose detection is in great need. A hydrothermal reaction of 2,6-naphthalenedicarboxylic acid (H2NDBC) with Tb3+ gave out a terbium coordination polymer, [Tb(NDBC)(COO)] (Tb-NDBC). Tb-NDBC featured combined emissions related with the intraligand charge transition of NDBC2‒ and characteristic 5D4→7F5 transition of Tb3+. The influences of response time, pH, and MOF dosage on the detection performances of DPA were explored and optimized. The sensitivity test of Tb-NDBC revealed a linear response of I545/I394 = 0.00728·CDPA + 0.63237 with limit of detection (LOD) of 5.21 µM in the linear range of 0-400 µM. It also showed a high selectivity that nine amino acids did not affect its detection performances. Tb-NDBC showed high sensitivity and selectivity to DPA detection in human serum and natural lake water. The paper-based sensor of Tb-NDBC displayed visible emission color conversions at 90 μΜ, and a linear equation of G = 0.77533∙CDPA + 139.66 through recognizing the green values (G) of the paper-based sensor. A smartphone APP was programmed based on the linear equation and the returned CDPA from the APP were close to theoretical values, showing the potential in DPA on-site detection.