Valence engineering enables cobaltosic oxide enhanced peroxidase-mimicking activity for efficiently detecting dopamine

Nanozymes as a promising alternative to natural enzymes are attracting enormous attention in past decades, yet their catalytic activities remain inferior to natural enzymes owing to the difficulties in performance improvement and precise control over composition, which greatly limits their practical application. Herein, by using metal organic frameworks as the sacrificial templates, we arbitrarily synthesize cobaltosic oxide (Co3O4) nanostructures with tunable valence states of Co sites via a one-step pyrolysis facilitated by a post-thermal treatment. It is found that through balancing the content between Co3+ and Co2+, partially reduced Co3O4 (R-Co3O4) exhibits the optimal peroxidase-like activity similar to natural horseradish peroxidase with Co2+ catalytically decomposing H2O2 while Co3+ adsorbs 3,30,5,50-tetramethylbenzidine. In addition, R-Co3O4 shows good stability in wide pH (2.58–10.04) and temperature (25.5–64.5 °C) ranges. Based on R-Co3O4 nanozymes, disposable paper-based bioassays are subsequently designed, exhibiting a good sensitivity to dopamine with a paper-based detection limit estimated to be 1.4 μM.