In this article, polydopamine (Pdop) functionalized multiwalled carbon nanotubes (MWCNTs@Pdop) were firstly synthesized and employed as the template for the dispersion of Pt nanoparticles to form Pt/MWCNTs@Pdop hybrid nanocomposite. The characterizations of the Pt/MWCNTs@Pdop were investigated by SEM, transmission electron microscopy, x‐ray diffraction, and voltammetry. Based upon the Pt/MWCNTs@Pdop nanocomposite, a modified carbon disk electrode was fabricated and successfully applied to the simultaneous detection of four important monoamines, including dopamine, epinephrine, norepinephrine, and serotonin, using capillary electrophoresis—amperometric detection system. Compared with the bare electrode, the four analytes at the Pt/MWCNTs@Pdop electrode exhibited higher sensitivity, broad linear responses from 0.5 to 1.0 × 102 nmol/L. The detection limits (S/N = 3) were lower than 9.2 × 10−10 mol/L. More importantly, the effect of noise exposure on monoamines (MAs) in hippocampus and hypothalamus was investigated for the first time. Compared with the control group, the levels of the MAs all varied to different extents after rats receiving the same noise stimulation. The results showed that the proposed method could be applied to the determination of low levels of MAs in biological samples and screening the target molecules for the diagnosis and treatment of various related diseases.