Polydopamine-Coated Co(3)O(4) Nanoparticles as an Efficient Catalase Mimic for Fluorescent Detection of Sulfide Ion

Surface engineering of nanozymes has been recognized as a potent strategy to improve their catalytic activity and specificity. We synthesized polydopamine-coated Co(3)O(4) nanoparticles (PDA@Co(3)O(4) NPs) through simple dopamine-induced self-assembly and demonstrated that these NPs exhibit catalase-like activity by decomposing H(2)O(2) into oxygen and water. The activity of PDA@Co(3)O(4) NPs was approximately fourfold higher than that of Co(3)O(4) NPs without PDA, possibly due to the additional radical scavenging activity of the PDA shell. In addition, PDA@Co(3)O(4) NPs were more stable than natural catalase under a wide range of pH, temperature, and storage time conditions. Upon the addition of a sample containing sulfide ion, the activity of PDA@Co(3)O(4) NPs was significantly inhibited, possibly because of increased mass transfer limitations via the absorption of the sulfide ion on the PDA@Co(3)O(4) NP surface, along with NP aggregation which reduced their surface area. The reduced catalase-like activity was used to determine the levels of sulfide ion by measuring the increased fluorescence of the oxidized terephthalic acid, generated from the added H(2)O(2). Using this strategy, the target sulfide ion was sensitively determined to a lower limit of 4.3 µM and dynamic linear range of up to 200 µM. The fluorescence-based sulfide ion assay based on PDA@Co(3)O(4) NPs was highly precise when applied to real tap water samples, validating its potential for conveniently monitoring toxic elements in the environment.