Protein-sized nanozymes «artificial peroxidase» based on template catalytic synthesis of Prussian Blue

• Protein-sized nanozymes (∅ = 4 – 6 nm) with peroxidase-like activity. • Template synthesis of Prussian Blue/polyaniline composites in reverse micelles. • Size-dependence of catalytic rate constants. • Hydrogen peroxide sensors based on protein-sized nanoparticles. We report on Prussian Blue based nanozymes, comparable in size with the natural enzyme peroxidase. Protein-sized nanoparticles have been synthesized in course of reduction ferric ion (Fe 3+ ) and ferricyanide ([Fe(CN) 6 ] 3- ) one-to-one mixture in reversed micelles (isooctane|AOT|water) used as templates. Aniline chosen as the best reductant for this aim has led to formation of composite (according to Raman spectroscopy) Prussian Blue – polyaniline nanoparticles. The protein-like size of the nanoparticles (∅ = 4 – 6 nm) has been confirmed by DLS and TEM imaging. Kinetic investigations of peroxidase-like activity in reversed micelles resulted in catalytic rate constant belonging to the same size-dependence as regular bulk catalytically synthesized nanozymes (slope ≈ 2.6), allowing to denote the reported Prussian Blue nanoparticles synthesized in reversed micelles as nanozymes «artificial peroxidase». Hydrogen peroxide sensors made by dipping the suspension of the latter onto the electrode support, displayed twice higher sensitivity as compared to the Prussian Blue film-based ones. Protein-sized nanozymes «artificial peroxidase» would obviously provide an advantage over regular nanozymes in (bio)sensors and analytical kits.