3D flower-like ferrous(II) phosphate nanostructures as peroxidase mimetics for sensitive colorimetric detection of hydrogen peroxide and glucose at nanomolar level.

Ferrous(II) phosphate nanoflowers (Fe3(PO4)2·8H2O NFs) were synthesized by a facial co-precipitation method. The structure, composition and morphology were characterized by XRD, EDX, element mapping and FESEM. The as-prepared Fe3(PO4)2·8H2O NFs exhibited excellent intrinsic peroxidase-like activity. Steady-state kinetic studies showed that Fe3(PO4)2·8H2O NFs exhibited stronger affinities with 3,3,5,5-tetramethylbenzidine (TMB) and H2O2 as the substrates compared with the natural horseradish peroxidase (HRP) and the catalytic constant (kcat) value was even higher than HRP and other reported nanomaterial based peroxidase mimics. The investigation of the catalytic mechanism by cyclic voltammetry, fluorescence spectroscopy and ESR displayed the catalytic activity of Fe3(PO4)2·8H2O NFs originated from the generation of •OH. The Fe3(PO4)2·8H2O NFs also exhibited higher robustness and better storage stability than HRP. Then, a Fe3(PO4)2·8H2O NFs-based colorimetric platform was developed to determine H2O2 and glucose. The linear range of H2O2 and glucose was as broad as 1 × 10-5-2.5 mM and 8 × 10-4-1.2 mM, and the detection limit (LOD) was as low as 5 nM and 35 nM, respectively. This simple assay offered a highly sensitive and specific strategy for H2O2 and glucose determination, which had been successfully utilized for real sample analysis with good reproducibility and accuracy.