Advances in stem-cell-derived neuronal models have opened new possibilities for drug discovery and disease modeling; however, functional evaluation of dopaminergic activity remains a critical bottleneck in assessing neuronal maturity. To address this challenge, SIDNEY (Smart Interfacial Dopamine-sensing platform for NEurons and organoid physiologY) is presented as a graphene oxide-wrapped hierarchical gold nanopillar hybrid that enables label-free, non-destructive electrochemical monitoring of dopamine (DA) under live-cell conditions. The electrode features a hierarchical nanostructure consisting of vertically aligned gold nanopillars (primary structure) decorated with smaller gold nanoparticles (secondary nanostructure), all wrapped with a thin layer of graphene oxide. This multiscale architecture provides enhanced conductivity, a large electroactive surface area, and molecular selectivity, while supporting long-term culture and differentiation of SH-SY5Y and iPSC-derived dopaminergic neurons directly on the electrode surface. SIDNEY achieves a limit of detection of 29.5 nm in phosphate-buffered saline and 7.51 nm in artificial cerebrospinal fluid, exhibiting high selectivity against interferents through π–π stacking, hydrogen bonding, and electrostatic interactions. Beyond conventional neuronal models, SIDNEY also enables real-time functional assessment of dopaminergic activity in midbrain organoids without labeling or sample destruction. This platform establishes a practical strategy for quantitative neurochemical monitoring, offering broad utility in drug screening and neurodegenerative disease research.