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The accurate and simultaneous detection of neurotransmitters, such as dopamine (DA) and epinephrine (EP), is of paramount importance in clinical diagnostic fields. Herein, we developed cerium-molybdenum disulfide nanoflowers (Ce-MoS 2 NFs) using a simple one-pot hydrothermal method and demonstrated that they are highly conductive and exhibit significant peroxidase-mimicking activity, which was applied for the simultaneous electrochemical detection of DA and EP. Ce-MoS 2 NFs showed a unique structure, comprising MoS 2 NFs with divalent Ce ions. This structural design imparted a significantly enlarged surface area of 220.5 m 2 g -1 with abundant active sites as well as enhanced redox properties, facilitating electron transfer and peroxidase-like catalytic action compared with bare MoS 2 NFs without Ce incorporation. Based on these beneficial features, Ce-MoS 2 NFs were incorporated onto a screen-printed electrode (Ce-MoS 2 NFs/SPE), enabling the electrochemical detection of H 2 O 2 based on their peroxidase-like activity. Ce-MoS 2 NFs/SPE biosensors also showed distinct electrocatalytic oxidation characteristics for DA and EP, consequently yielding the highly selective, sensitive, and simultaneous detection of target DA and EP. Dynamic linear ranges for both DA and EP were determined to be 0.05~100 μM, with detection limits (S/N = 3) of 28 nM and 44 nM, respectively. This study shows the potential of hierarchically structured Ce-incorporated MoS 2 NFs to enhance the detection performances of electrochemical biosensors, thus enabling extensive applications in healthcare, diagnostics, and environmental monitoring.

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.