Lanthanide-based luminescent metal-organic framework as an optical sensing platform for rapid and reliable assessment...

A rapid and sensitive fluorescence-based method for antioxidant capacity assessment was developed using a lanthanide-based metal-organic framework (LVMOF-1). The Eu³⁺-MOF, incorporating an electron-deficient viologen ligand, enables host-guest interactions with phenolic antioxidants, leading to a quantitative quenching of a composite optical signal driven by a resonance convolution of native Eu³⁺ photoluminescence and second-order scattering, inner filter effect and colloidal modulation. Using gallic acid as a model compound, the system exhibited a non-linear Langmuir-type response that was successfully linearized through logarithmic transformation, enabling reliable quantification of total antioxidant capacity over an extended concentration range. The method showed excellent analytical performance, with a limit of detection of 0.0077 mg L^-1, good linearity (R² = 0.992), and reproducibility below 7% RSD. Compared to conventional assays (Folin-Ciocalteu, DPPH, ABTS, and FRAP), it provided higher sensitivity, shorter analysis time (≤ 2 min), and improved robustness in complex matrices, inherently minimizing color-induced spectral interferences due to the high sensitivity of fluorescence detection. Application to honey, tea, and wine samples showed very strong correlations with established methods (Pearson r = 0.947-0.996). These results were further supported by Bland-Altman analysis, which confirmed good overall agreement with method-dependent differences, and principal component analysis (PCA), which revealed a common underlying antioxidant capacity dimension. Additionally, the LVMOF-1 assay showed the best greenness (AGREE score 0.59) and lowest cost (0.63 € per sample), highlighting its potential as a sustainable alternative for routine antioxidant screening.