Piezoelectric BaTiO3 nanoparticles as oxidase mimics breaking pH limitation for colorimetric detection of glutathione reductase

Piezoelectric nanozymes driven by available ultrasonic (US) irradiation are receiving considerable attention for the reactive oxygen species (ROS)-enabled ability that depends on intrinsic polarization and energy-band tilting. In this work, piezo-response barium titanate (BaTiO3) nanoparticles (NPs) were successfully constructed and used as oxidase mimics to clarify the underlying mechanism between the piezoelectric effect and enzyme-like properties. Under US activation, BaTiO3 NPs can generate a built-in electric field inside the materials, which promotes electron-hole pairs separation and initiates the cascade redox reactions with surrounding molecules (e.g., H2O and O2) to yield multiple ROS. In the absence of H2O2 or dissolved oxygen, the synthesized BaTiO3 NPs displayed exceptional oxidase-like activity at neutral pH and could catalyze the chromogenic reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) with a high catalytic constant (Kcat) as 2.11 × 103 s−1. Fascinatingly, glutathione (GSH) inhibited the TMB oxidation owing to its strong reducibility, based on which, a colorimetric assay for glutathione reductase (GR) detection could be rationally achieved. The linear range and detection limit were determined to be 0.01–1 U/mL and 0.0092 U/mL, respectively. This study not only unveils the essential mechanism of piezocatalysis-nanozyme coupling process, but also blazes a new pathway for the rational design of nanozymes with high activity for biochemical analysis.