A post-modified metal-organic framework ZIF-90-AN as “turn-on” fluorescence probe for the highly selective and ultra-sensitive quantitative detection of common trivalent metal cations

A post-modified metal organic framework (ZIF-90-AN) was designed and synthesized by grafting of 1, 2, 4-triazine-3-amine (AN) onto ZIF-90 via Schiff base reaction. ZIF-90-AN retains the original crystal structure of ZIF-90 with good chemical and thermal stability. ZIF-90-AN in ethanol exhibited highly selective and ultra-sensitive "turn-on" fluorescence responses towards five common trivalent metal cations (Cr3+, Fe3+, Al3+, Ga3+, In3+) over the other competitive metal ions accompanied by the obvious fluorescence color changes. The fluorescence intensity of ZIF-90-AN showed a linear relationship with the concentration of trivalent metal cations with low detection limits of 4.01 μM for Cr3+, 2.08 μM for Fe3+, 1.72 μM for Ga3+, 5.73 μM for In3+ and 2.32 μM for Al3+, respectively. In addition, ZIF-90-AN can easily identified five trivalent metal cations in the test paper mode with naked eyes. Furthermore, the satisfying accuracy and recovery of ZIF-90-AN in detecting Cr3+ and Al3+ in real water samples and human serum confirmed the practical application capability. This work proves that the post-modification on MOF is an efficient approach to prepare the fluorescence probe for identification and detection of metal ions in practical samples.