As dopamine is an important neurotransmitter involved in neural signaling and certain diseases, it is crucial to detect it in patients to regulate bodily functions. In this study, novel S-doped, P-doped, and S,P-co-doped graphene oxide pencil graphite electrodes were prepared in a single step via the chronoamperometric method for use in a dopamine sensor. The anodic oxidation potentials of dopamine, uric acid, and caffeine were observed to be distinct from one another in the presence of the others by the fabricated S,P-co-doped GO/PGE. This enables its use as a new electrochemical sensor for the selective determination of DA, UA, and CAF. In a 0.1 M phosphate buffer solution at pH 7.4, the oxidation current increased linearly over the concentration range from 0.01 µM to 0.001 M DA. The limit of detection (LOD) obtained by DPV was 14.5 nM, and the limit of quantification (LOQ) was 48.5 nM. The applicability of the fabricated S,P-co-doped GO/PGE electrode was successfully demonstrated in the determination of DA in commercial pharmaceutical samples. Promising results were observed, with a recovery range of 100–105%, indicating that this could be a valuable platform for developing additional enzyme-free electrochemical sensors.