Dopamine (DA), an organic chemical neurotransmitter in the human brain, plays important roles in neuronal reward, motor control, and decision making. Thus, accurate quantification of DA concentration is essential for the investigation of various dopaminergic neural circuits and diagnosis of neurological diseases. Herein, we report an overoxidized polypyrrole/sodium dodecyl sulfate (SDS)-modified multi-walled carbon nanotube (OPPy/SDS-CNT) electrode which allows detection of DA with high resolution and selectivity. By using SDS as a dopant and sodium hydroxide (NaOH) as an oxidizing agent, highly sensitive detection of DA down to 5 nM with a detection limit of 136 pM is achieved. Moreover, due to the strong electrostatic interaction between the negatively-charged electrode and the positively-charged DA molecules, selective electrochemical detection of DA is successfully demonstrated in the presence of ascorbic acid (AA) and glucose (Glc). Lastly, by demonstrating in vitro detection of DA secreted from dopaminergic cells (PC12 cells) and examining biocompatibility of the electrode, we show the potential of our OPPy/SDS-CNT electrode as a promising candidate for a functional neural interface for in vitro and in vivo monitoring of DA concentrations.