Ferroelectric BaTiO3 nanoparticles as peroxidase mimics for colorimetric detection of glutathione S-transferase at physiological pH

The long-standing challenges in peroxidase-mimicking nanozymes catalysis lie in their generally lower catalytic activity in comparison to natural enzymes, as well as only exhibiting specific activities within acidic environments. Herein, BaTiO₃ nanoparticles (BTO NPs) operated optimally at a physiological pH and exhibited excellent peroxidase-like activity with the catalytic constant (K_cat) up to 1.99×10⁴ s⁻¹ and 9.41×10³ s⁻¹ for 3,3′,5,5′-tetramethylbenzidine (TMB) and H₂O₂ substrate, respectively, which is fourfold and twofold that of horseradish peroxidase (4.00×10³ s⁻¹ and 3.48×10³ s⁻¹). Mechanism studies suggested that BTO NPs generated internal electric fields due to spontaneous polarization, which drove free carrier separation in different directions. The free carriers led to redox reactions with H₂O₂ and dissolved oxygen, which produced a variety of reactive oxygen species (ROS), such as ^•OH, ¹O₂ and O₂^•⁻, thus effectively oxidizing the chromogenic substrates. Furthermore, due to its strong reducing property, glutathione (GSH) can inhibit the oxidation of TMB. Conversely, glutathione S-transferase (GST) reduces the inhibition of GSH by facilitating the reaction between GSH and 1-chloro-2,4-dinitrobenzene. Ultimately, a colorimetric method was established for the detection of GST at physiological pH, with a linear range of 0.025 − 5.0 U·L⁻¹. This work demonstrated the great promise of screening novel peroxidase mimics with super activities from ferroelectric materials.