The monoamine neurotransmitter dopamine-containing cells originate at the brain’s mesencephalic-diencephalic junction and project to several forebrain targets. Within the central nervous system, dopamine plays a crucial role in reward, motivation and motor control. In the periphery, it is involved in renal vasodilation, natriuresis, and diuresis. Dysfunction in dopaminergic neurotransmission has been implicated in several neurological and psychiatric conditions including mood disorders, schizophrenia, Parkinson's disease, and obsessive-compulsive disorder. It is imperative to understand the property of such a key brain molecule. Therefore, here, we use a continuous-wave (CW) laser closed-aperture (CA) Zscan technique to unravel the nonlinear property of dopamine at physiological condition (pH~7.4). Interestingly, we observe that dopamine shows nonlinearity when exposed to various input laser intensity. We attribute the origin of observed nonlinearity majorly governed by saturated atomic absorption mechanism along with insignificant contribution from thermal lensing effect. Our approach is simple and robust, and our observations have opened up new avenues for investigating dopaminergic processes by utilizing its nonlinear property. This study is of immense importance to researchers in the fields of nonlinear optics, biophysics, and neuroscience.