A water-stable MOF-AgClO₄-abtz as fluorescent sensor for detection of folic acid based on inner filter effect

Folic acid (FA, Vitamin B9), as a water-soluble chemical compound of the vitamin B groups, plays an important role to human health. Thus, it is of great significance to develop sensitive assays for detection of FA. Herein, we prepared a water-stable metal-organic frameworks {[Ag₂(μ₂-abtz)(μ₃-abtz)(ClO₄)]⋅(ClO₄)}_n (MOF-AgClO₄-abtz; abtz = 1-(4-aminobenzyl)-1, 2, 4,-triazole) material, which exhibited a high fluorescent quantum yield of 78.97%, good water dispersibility and excellent chemical stability. Then MOF-AgClO₄-abtz was developed as a "turn-off" fluorescent sensor for detection of FA via inner filter effect (IFE). The IFE mechanism was mainly originated from the spectrum overlap between fluorescence emission of MOF-AgClO₄-abtz at 350 nm and UV-vis absorption band of FA ranging from 340 to 360 nm, resulting in fluorescence quenching. Furthermore, the proposed method exhibited a good linear response to FA in the concentration range of 0.1-30 μM, and the limit of detection (LOD) was calculated to be 49 nM (S/N = 3). The great reproducibility of the method was checked for three replicate detections of 20 μM FA to find relative standard deviation (RSD) of 3.4%. This method also exhibited excellent long-term stability by detecting 30 μM FA for 7 days, the RSD value was obtained to be 2.8%. Ultimately, this method was employed for sensitive detection of FA in human serum and plasma samples with quantitative spike recoveries ranging from 95.3% to 104.6%.