Dopamine (DA) is a catecholamine neurotransmitter that can cause some nervous system disorders, leading to Parkinson's disease. Thus, the development of a dopamine sensor is important for the diagnosis of these disorders. Here, we studied the adsorption of DA on semiconducting single-walled carbon nanotubes (SWNTs), including pure, and B,N co-doped (6,5) SWNTs, via DFT calculations. Our results indicated that DA can form multiple molecular interactions with pure (6,5) SWNT. However, these interactions have limited effects on the electronic properties; therefore, the band gap and conductivity of pure (6,5) SWNT did not change significantly after DA adsorption. On the other hand, regarding the adsorption of DA on a B,N co-doped (6,5) SWNT, we found that not only stronger molecular interactions such as C-H center dot center dot center dot pi interactions were established but also an N-DA-B dative bond between DA and the SWNT was formed, altering the electronic properties of this SWNT. These cooperative interactions after DA adsorption caused much more pronounced changes in the band gaps and conductivities of B,N co-doped (6,5) SWNTs than in those of pure (6,5) SWNT. Our results demonstrated that the sensitivity of a pure (6,5) SWNT to detect dopamine was enhanced in the B,N co-doped (6,5) SWNT.