Antimonotungstate-Based\nHeterometallic Framework Formed\nby the Synergistic Strategy of In Situ-Generated Krebs-Type Building\nUnits and the Substitution Reaction and Its High-Efficiency Biosensing\nKRAS Gene

A novel antimonotungstate (AT)-based heterometallic framework\n{[Er(H<sub>2</sub>O)<sub>6</sub>]<sub>2</sub>[Fe<sub>4</sub>(H<sub>2</sub>pdc)<sub>4</sub>(B-β-SbW<sub>9</sub>O<sub>33</sub>)<sub>2</sub>]}·50H<sub>2</sub>O (<b>1</b>, H<sub>2</sub>pdc\n= pyridine-2,5-dicarboxylic\nacid) was obtained through a synergistic strategy of in situ-generated\ntransition-metal-encapsulated polyoxometalate (POM) building units\nand the substitution reaction. Its structural unit is composed of\na tetra-Fe<sup>III</sup>-substituted Krebs-type [Fe<sub>4</sub>(H<sub>2</sub>pdc)<sub>4</sub>(B-β-SbW<sub>9</sub>O<sub>33</sub>)<sub>2</sub>]<sup>6–</sup> subunit and two [Er(H<sub>2</sub>O)<sub>6</sub>]<sup>3+</sup> cations. This subunit can be regarded as a\nproduct of carboxylic oxygen atoms of H<sub>2</sub>pdc ligands replacing\nactive water ligands in the [Fe<sub>4</sub>(H<sub>2</sub>O)<sub>10</sub>(B-β-SbW<sub>9</sub>O<sub>33</sub>)<sub>2</sub>]<sup>6–</sup> species. Apparently, the substitution action of carboxylic oxygen\natoms of H<sub>2</sub>pdc ligands for active water ligands, together\nwith the coordination function of Er<sup>3+</sup> ions, plays a connection\nrole in the architecture of the three-dimensional (3-D) heterometallic\nframework. Based on the stability and high redox activity of <b>1</b>, a glassy carbon electrode modified by <b>1</b> is\nused for the construction of an electrochemical biosensor (ECBS).\nThus, such <b>1</b>-based ECBS can sensitively detect the KRAS\ngene (a key genetic marker for identifying the occurrence of malignant\ntumors) and displays a low detection limit (0.106 pM), high selectivity,\nand reproducibility. This work not only provides a feasible approach\nto prepare novel multicomponent POM-based heterometallic frameworks\nbut also establishes a new platform for biosensing the KRAS gene and\nextends the application scope of POM-based functional materials.