Mechanism of ferrous ions reversibly inhibiting of oxidase-Like activity of Co3O4 nanowires and its application in horticultural fertilizer analysis

Nanozymes are becoming substitutes of some natural enzymes due to their excellent properties, however, little attention has been paid to the catalytic mechanisms and especially inhibition mechanism of nanozymes, which impeded advancement in nanozymes and their wide application including bioanalysis. Herein, non-toxic filamentous virus, M13 phage templated Co3O4 nanowires (NWs) was facilely prepared, which exhibits excellent oxidase (OXD)-like activity and catalytic efficiency. The catalytic mechanism of OXD-like is oxygen vacancies, confirmed by high resolution X-ray photoelectron spectrum of O 1 s, electron paramagnetic resonance spectra and reactive oxygen species scavenging experiments. The substrate of 3,3′,5,5′-tetramethylbenzidine (TMB) for OXD-like is oxidized into blue ox-TMB, and then turned to yellow diimine, depending on TMB concentration and incubation time. Then the mechanism of ferrous ions (Fe2+) inhibition of the oxidase-like activity of Co3O4 NWs was uncovered that Fe2+ competes with TMB for oxygen vacancies. The inhibition is reversible with the type of hybrid of competitive inhibition and non-competitive inhibition with the inhibition constants (KI and KI') of 0.134 mM and 1.012 mM, respectively. Finally, on the basis of the inhibitory effect, a fast, selective and sensitive Fe2+ colorimetric analysis was proposed with two linear parts and a limit of detection of 0.21 μM Fe2+ (S/N = 3), which is applicable to detect Fe2+ in horticultural fertilizers. This study may offer a new strategy for the in-depth study of inhibition mechanism of other nanozymes, which would extend the scope of nanozyme-based biosensing.