Two dimensional iron metal-organic framework nanosheet with peroxidase-mimicking activity for colorimetric detection of hypoxanthine related to shrimp freshness

Two dimensional iron metal-organic framework nanosheet (2D Fe MOF) was facilely synthesized at room temperature by simple stirring of iron salts and terephthalic acid ligand in a mixed solution containing triethylamine. Its morphology and structure were fully characterized by TEM, AFM, XPS and TEM element mapping. Then, its peroxidase-mimicking activity was studied by using H₂O₂ and 3, 3', 5, 5'- tetramethylbenzidine as substrate. K_m and V_max of 2D Fe MOF towards H₂O₂ were 0.02 mM and 2.08 × 10^-8 M s^-1, respectively. Through the formation of cascade reaction between xanthine oxidase and 2D Fe MOF, a visual method for hypoxanthine (Hx) detection was constructed to evaluate aquatic products freshness. After effective validation, this method presented wide linear range (5.0-500.0 μM), low limit of detection (3.29 μM), satisfied accuracy (recovery of 94.78-99.85%), and good selectivity. By using this method, Hx content in shrimp samples at different storage time were determined.