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[Display omitted] • Bi 2 Fe 4 O 9 nanozyme as a simple and low-cost colorimetric sensor was developed for easy dopamine detection. • The sensor achieved good performance with a linear range from 0.15 to 50 μM and a detection limit of 51 nM. • The nanozyme was reused up to 4 cycles without a significant decrease in its performance. This work describes the preparation of ternary bismuth ferrite oxide nanoparticles (Bi 2 Fe 4 O 9 NPs) with an enzyme mimetic activity for dopamine (DA) qualitative and quantitative detection. Bi 2 Fe 4 O 9 NPs were prepared using a facile, low cost, and one-pot hydrothermal treatment. The chemical composition, morphology, and optical properties of Bi 2 Fe 4 O 9 nanozyme were characterized using different techniques such as Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction pattern (XRD), X-ray photoelectron spectroscopy (XPS), thermo-gravimetric analysis (TGA), dynamic light scattering (DLS), field-emission scanning electron microscopy (FESEM) imaging, FESEM-energy dispersive X-ray spectroscopy (EDS), UV–vis absorption, and fluorescence emission spectroscopy. Bi 2 Fe 4 O 9 NPs were utilized to catalyze the oxidation of a typical chromogenic peroxidase substrate, 3,3′,5,5′-tetramethylbenzidine (TMB), to form the blue-colored oxidized product (oxTMB), in the presence of hydrogen peroxide (H 2 O 2). All reactions occurred in acetate buffer solution (pH 3.5) to generate hydroxyl radicals (•OH) and the kinetics were followed by UV–vis absorbance at 654 nm. The steady-state kinetic parameters were obtained from the Michaelis-Menten equation and exhibited a good catalytic efficiency of Bi 2 Fe 4 O 9 NPs as enzyme mimetics. Michaelis–Menten constant (K m) values were estimated as 0.07 and 0.73 mM for TMB and H 2 O 2 , respectively. The presented method is efficient, rapid, cost-effective, and sensitive for the colorimetric detection of dopamine with a linear range (LR) from 0.15 to 50 μM and a detection limit (LOD) of 51 nM. The proposed colorimetric sensor was successfully applied for the detection of different concentrations of dopamine in spiked fetal bovine serum (FBS) and horse serum (HS) samples. It is anticipated that Bi 2 Fe 4 O 9 nanozyme holds great potential in biomedical analysis and diagnostic applications of dopamine-related diseases. [ABSTRACT FROM AUTHOR]