Oxygen vacancies rich Co-Mo metal oxide microspheres as efficient oxidase mimetic for colorimetric detection of sulfite

Modulation of surface oxygen vacancies (Ov) by defect engineering is an attractive strategy for designing high performance transition metal oxide nanozymes. In this work, we reported the fabrication of the CoMoO4 oxidase-like nanozyme, i.e. CoMo-300r, by first pyrolyzing the CoMo layered double hydroxide precursor in an air atmosphere at 300 °C and subsequent NaBH4 reduction strategy. Various characterization outcomes confirm the mesoporous structures of both CoMo-300r and no NaBH4 treated CoMo-300, while the specific surface area of CoMo-300 is significantly increased from 103.54 m2·g−1 to 165.24 m2·g−1 after NaBH4 reduction. Also, NaBH4 reduction treatment leads to the formation of Ov rich CoMoO4 and reduced metal ion species on the surface, promoting the redox reaction kinetics. The CoMo-300r prepared at a molar ratio of Co to Mo of 1:2, pyrolysis temperature of 300 °C and 10 mM NaBH4 exhibited the best oxidase-like activity. The oxidase-like activity of CoMo-300r is 2.6-fold times that of no NaBH4 treated optimal CoMo-300. The CoMo-300r can effectively promote TMB oxidation to produce blue color and has the Michaelis-Menten constant of 0.0428 mM, which was lower than most cobalt-based oxide nanozymes and indicated a higher affinity for TMB. In terms of inhibition of SO32− on the CoMo-300r/TMB system, a sensitive SO32− colorimetric sensing platform was established. The linear range and limit of detection for sulfite determination were 0.2–40 μM and 0.09 μM, respectively. The relative standard deviation for the determination of 10 μM sulfite was 1.41% (n = 11). The method was successfully applied to the detection of sulfite in white wine. This work provides a new strategy to fabricate high activity oxidase mimetic for food analysis.