Water Stable [Tb₄] Cluster-Based Metal-Organic Framework as Sensitive and Recyclable Luminescence Sensor of Quercetin

A novel 3D metal-organic framework (MOF){[Tb₃(CBA)₂(HCOO)(μ₃-OH)₄(H₂O)]·2H₂O·0.5DMF} _n (S-1) was synthesized by the solvothermal method. The crystal structure indicates that [Tb₄O₄] cubane clusters self-assemble into an infinite chain by sharing vertex, which is further linked to adjacent chains through 1,1-cyclobutanedicarboxylic acid ligand (H₂CBA), resulting in a honeycomb arrayed framework. S-1 possesses excellent water stability and still retains intact structure after exposure to water for 10 weeks or boiling water for 10 weeks. Interestingly, S-1 acts as a luminescence sensor to selectively and sensitively detect quercetin with the limit of detection (LOD) as low as 0.23 ppm (7.6 × 10^-7 M). The relationship between relative luminescence intensity and concentration obeys linear in the range of 0-300 ppm (0-993 μM), which allows quantitative detection of quercetin. Importantly, S-1 can be reused at least six times with almost no change in luminescent intensity. Compared with the high performance liquid chromatography-mass spectrometry (HPLC-MS) method, S-1 was used to determine the content of quercetin in onionskin and apple peel samples with satisfactory results. Furthermore, a portable S-1 test paper is also developed and expected to be applied in practice. To our knowledge, S-1 is the first example of MOFs as luminescent sensor for quercetin.