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

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.