A multifunctional fluorescence MOF material: Triple-channel pH detection for strong acid and strong base, recognition of moxifloxacin and tannic acid

A luminescent 1D metal–organic framework [Co(apba)2(H2O)2] (1) was solvothermal synthesized by using 4-(2-aminopyrimidine-5-yl)benzoic acid (Hapba) as ligand. 1 showed pronounced sensing properties with triple-channel specific recognition ability for strong acid-base and weak acid. From pH = 3.5 to 2.0, the fluorescence quenching percentage reached 1064 % per pH at 412 nm due to the protonation of –NH2. In the pH region of 3.5–4.5, 1 realizes wavelength-based pH detection depending on the wavelength shift of 30 nm from 412 nm to 382 nm originating from the protonation of nitrogen atom in pyrimidine. In the pH range of 11.5–13.4, the fluorescence quenching percentage reached 2099 % per pH relying on the interaction between OH– and uncoordinated oxygen atom on carboxylate group. This is the first example that a MOF-based pH sensor can detect strong acid-base and weak acid, and their sensitivity to pH is likewise the highest among all pH fluorescent sensors. 1 can also detect antibiotic moxifloxacin (MOX) and polyphenol compound tannic acid (TA) with the limit of detection (LOD) at the 10 ppb level. In the recognition of 1 for MOX, KSV is 2.05 × 105 M−1 (0–100 μM) and LOD reaches 43 nM, which is the first case of a MOF-based MOX sensor so far. The fluorescence response of 1 to TA is also apparent with the KSV value of 7.55 × 105 M−1 (0–0.05 μM) and LOD of 11 nM. This is as well the only instance of MOF material sensing TA to date. Moreover, 1 can continuously track MOX and TA for up to 90 days. The sensing mechanisms of pH, MOX, and TA are also discussed in detail.