In this study we have developed a highly sensitive optical sensor for the detection of epinephrine using carbon dots co-doped with samarium and nitrogen (Sm,N-CDs) with a very low detection limit of 28.1 nM and a broad linear dynamic range from (0–105 nM). Various techniques were employed to characterize the synthesized material, aiming to understand its morphological and physicochemical characteristics. The synergistic effect of the synthesized Sm,N-CDs demonstrated excellent optical performance, high selectivity and photostability. Additionally, good recovery findings were obtained when the sensor’s viability for Epinephrine detection in biological fluid samples that had been spiked was evaluated. In addition, we have developed an smartphones-based sensor to record the solution’s fluorescent color shift as it is being sensed. Using a mobile phone application to examine the green, red, and blue values from these photos, the comparable LOD was found to be 17.21 μM in a (0–90 μM) wide linear range of concentration. This straightforward, affordable, and quick screening device is highly demanding for the on-the-spot identification of the analytes at remote locations where advanced instrumentation is typically unavailable. Density functional theory was used to examine energy, stability, band gap, and how Ep interacted with the Sm,N-CDs nanoparticles.