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 Na 4 [Ho(H 2 O) 6 ] 2 [Fe 4 (H 2 O) 2 (pic) 6 Ge 2 W 20 O 72 ]·16H 2 O ( 1 ) (Hpic = picolinic acid). The 1D polymeric chain of 1 is assembled from particular {Ge 2 W 20 }-based [Fe 4 (H 2 O) 2 (pic) 6 Ge 2 W 20 O 72 ] 10- segments through bridging [Ho(H 2 O) 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 H 2 O 2 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 H 2 O 2 , and then, H 2 O 2 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.