FeMoO₄ nanospheres-based nanozymatic colorimetry for rapid and sensitive pyrophosphate detection

Assays of pyrophosphate ion (PPi) are of remarkable biochemical significance due to their vital roles in the bioenergetic and metabolic processes or as disease indicators. Colorimetry is popular in the field of biosensing and detection because of its simplicity, speed and cost-effectiveness, but there is a lack of a suitable colorimetric probe. Herein, a novel colorimetric sensing platform has been established for the detection of pyrophosphate based on the FeMoO₄-H₂O₂-3,3',5,5'-tetra-methylbenzidine (TMB) system. Compared with most previously reported iron-based nanozymes, the as-obtained FeMoO₄ nanospheres with a rough surface possessed a much superior peroxidase-like catalytic activity (V_max = 28.47 × 10^-8 M s^-1) and substrate affinity (K_m = 0.174 mM) toward H₂O₂ catalysis. Due to the Fe(II) and PPi reaction, the presence of PPi could specifically restore blue oxidized TMB to colorless TMB, which led to a decrease in UV absorption at 652 nm. The absorbance change is proportional to the PPi concentration, with a linear detection range (from 0.5 to 25 μM) and a low detection limit of 0.3 μM (S/N = 3). Accordingly, its excellent selectivity and high sensitivity made it a potential colorimetric sensor for PPi analysis in actual water samples.