First Ultrathin Pure Polyoxometalate 2D Material as a Peroxidase-Mimicking Catalyst for Detecting Oxidative Stress...

Although two-dimensional (2D) materials with ultrathin geometry and extraordinary electrical attributes have attracted substantial concern, exploiting new-type 2D materials is still a great challenge. In this work, an unprecedented single-layer pure polyoxometalate (POM) 2D material (2D-1) was prepared by ultrasonically exfoliating a one-dimensional (1D)-chain heterometallic crystalline germanotungstate Na₄[Ho(H₂O)₆]₂[Fe₄(H₂O)₂(pic)₆Ge₂W₂₀O₇₂]·16H₂O (1) (Hpic = picolinic acid). The 1D polymeric chain of 1 is assembled from particular {Ge₂W₂₀}-based [Fe₄(H₂O)₂(pic)₆Ge₂W₂₀O₇₂]^10- segments through bridging [Ho(H₂O)₆]³⁺ cations. 2D-1 is formed by π-π interaction driving force among adjacent 1D polymeric chains of 1. Also, the peroxidase-mimicking properties of 2D-1 toward detecting H₂O₂ were evaluated and good detection result was observed with a limit of detection (LOD) of 58 nM. Density functional theory (DFT) calculation further confirms that 2D-1 displays outstanding catalytic activity and active sites are located on Fe centers and Hpic ligands. Under the catalysis of uricase, uric acid can be transformed to allantoin and H₂O₂, and then, H₂O₂ oxidizes TMB to its blue ox-TMB in the presence of 2D-1 as a catalyst. Then, we utilized this cascade reaction to detect uric acid, which also exhibits prominent results. This research opens a door to prepare ultrathin pure POM 2D materials and broadens the scope of potential applications of POMs in biology and iatrology.