Biomass‐Derived Fluorescent Carbon Quantum Dots for Effective Sensing of Dopamine and Lemon Yellow in Real Samples

Dopamine is a clinically significant neurotransmitter whose abnormal concentration is associated with neurological disorders, while lemon yellow is a widely used synthetic food dye that poses potential health risks when consumed beyond permissible limits. Thus, the selection of these two analytes establishes the versatility of the carbon quantum dots (CQDs) across biologically and environmentally relevant systems. In this work, fluorescent CQDs are synthesized from locally available sour spinach via a hydrothermal route and employed for the simultaneous detection of dopamine and lemon yellow. The as‐prepared CQDs are thoroughly characterized using fourier transform infrared spectroscopy (FTIR), UV–visible spectroscopy, transmission electron microscopy (TEM), and X‐ray photoelectron spectroscopy (XPS) analyses. These CQDs exhibit strong blue photoluminescence centered around 450 nm and show efficient fluorescence “turn‐off” responses toward both the aforesaid analytes. CQDs can detect the analytes in the micromolar range. The quenching arises primarily from static interactions between the oxidized dopamine or the chromophoric groups of lemon yellow and the CQDs in the ground state. The practical applicability of the sensor is demonstrated through the successful detection of dopamine in human serum samples and lemon yellow in commercially available soft drinks.