<p>A 3D neural network-shaped nitrogen-doped graphene-coated MnO₂ composite (N@Gr-MnO₂) was successfully prepared by hydrothermal method. The nitrogen content in graphene is effectively regulated by changing the amount of urea added. Upon achieving a graphene oxide (GO) to urea mass proportion of 1/200, the resultant N@Gr exhibited maximal nitrogen concentration. Moreover, XPS analyses confirmed that this configuration led to an apex in the total abundance of both pyridinic nitrogen and graphitic nitrogen, elements pivotal for catalytic proficiency. The N@Gr-MnO₂ was prepared by the combination of N@Gr (at the mass ratio of 1/200) and manganese dioxide and was used to construct an electrochemical sensor (N@Gr/α-MnO₂/GCE) to detect dopamine. There are two linear relationships between the current response of the sensor to DA concentration: the first section is 0.01 to 8.79&#xa0;μmol·L⁻¹, the corresponding linear equation and correlation coefficient (<i>R</i>²) are <i>I</i> (μA) = 7439.5 C (mmol·L⁻¹) + 2.27 and 0.986, respectively, and the sensitivity is 16,907.9 μA (mmol·L⁻¹) ⁻¹&#xa0;cm⁻². The second section of concentration is 11–104&#xa0;μmol·L⁻¹, and the corresponding linear equation and correlation coefficient (R²) are <i>I</i> (μA) = 2883.9 C (mmol·L⁻¹) + 45.5 and 0.995. The&#xa0;detection limit (S/N)&#xa0;of DA by N@Gr/α-MnO₂/GCE is 1.7&#xa0;nmol·L⁻¹. The&#xa0;sensor can be applied to the quantification detection of dopamine in human serum and urine, with a recovery percentage of&#xa0;92%, confirming its significant potential for real-world implementation.</p>