Triple-enzyme mimetic activity of Fe3O4@C@MnO2 composites derived from metal–organic frameworks and their application to colorimetric biosensing of dopamine

Novel Fe 3 O 4 @C@MnO 2 composites were successfully synthesized for the first time via an interfacial reaction between magnetic porous carbon and KMnO 4 , in which the magnetic porous carbon was derived from the pyrolysis of Fe-MIL-88A under N 2 atmosphere. Interestingly, the obtained Fe 3 O 4 @C@MnO 2 composites were found to have triple-enzyme mimetic activity including peroxidase-like, catalase-like, and oxidase-like activity. As a peroxidase mimic, Fe 3 O 4 @C@MnO 2 composites could catalyze the oxidation of TMB into a blue oxidized product by H 2 O 2 . As a catalase mimic, Fe 3 O 4 @C@MnO 2 could catalyze the decomposition of H 2 O 2 to generate O 2 and H 2 O. As an oxidase mimic, Fe 3 O 4 @C@MnO 2 could catalyze the direct oxidation of TMB to produce a blue oxidized product without H 2 O 2 . Reactive oxygen species measurements revealed that the oxidase-like activity originated from 1 O 2 and O 2 − ∙and little∙OH generated by the dissolved oxygen, which was catalyzed by the Fe 3 O 4 @C@MnO 2 in the TMB oxidation reaction. The oxidase-like activity of Fe 3 O 4 @C@MnO 2 was investigated in detail. Under the optimized conditions, a rapid, sensitive, visual colorimetric method for dopamine detection was developed based on the inhibitory effect of dopamine on the oxidase-like activity. The proposed method allows for dopamine detection with a limit of detection of 0.034 μM and a linear range of 0.125–10 μM. This new colorimetric method was successfully used for the determination of dopamine in human blood samples. Graphical abstract