Discriminative Detection of Dopamine and Tyrosinase Based on Polydopamine Dots Triggered by Fenton-like Activity of Mn₃O₄ Nanoparticles

In this work, the inherent Fenton-like activity of Mn3O4 nanoparticles (Mn3O4 NPs) was explored to catalyze the polymerization of dopamine to blue-emitting polydopamine dots (PDA-dots), which can be used for selective detection of dopamine (DA) and tyrosinase (TYR). It was demonstrated that Mn3O4 NPs sparklingly oxidized DA to its quinone derivatives at the same time decomposing hydrogen peroxide to hydroxyl radicals that controlled the polymerization to PDA-dots. Interestingly, Mn3O4 NPs retained high activity to produce PDA-dots after repeated use of five cycles. It was found that with the polymerization of DA, the FL intensity of the produced PDA-dots changes in a dose-dependent on dopamine concentration. Therefore, under the optimum conditions, a turn-on fluorometric detection was thereby established to detect dopamine, showing a linear range of dopamine concentration from 0.050 μM to 300 μM. The Mn3O4 NPs-assisted preparation of fluorescent PDA-dots was further exploited to detect TYR by using tyramine as its model substrate. This simple strategy showed a limit of detection of 0.0048 U/mL toward TYR and displayed a linear response in the concentration range from 0.021 to 13.43 U/mL. Importantly, this study not only provides insight into how to quickly synthesize polydopamine dots that would be explored in biomedical applications but also establish a method to obtain highly discriminative and sensitive detection of dopamine and tyrosinase.