Synthesis of Carbon Dots via Hydrothermal Reaction for Selective Detection of Serotonin

Serotonin (5-HT) is a significant neurotransmitter involved in the regulation of mood, social behavior, depression, and other neurological activities. In this work, we synthesized nitrogen-doped carbon dots using naturally occurring amino acids such as L-aspartic acid and L-cysteine by employing a one-step hydrothermal reaction. The amino acid-derived carbon dots (CDs) are called AACDs. The as-synthesized AACDs showed strong blue-color emission under UV light and photoluminescence (PL) emission maximum wavelength at 457 nm with an excitation wavelength of 344 nm. The AACDs had superior aqueous solubility due to the carboxyl (-COOH) and amine (-NH₂) functional groups on their surface. 5-HT could be detected by adding cobalt ions (Co²⁺) to the AACDs. The Co²⁺ ions facilitate cross-linking between free amino and carboxylate groups. Fluorescence quenching by AACDs incorporating Co²⁺ ion was observed to be dependent on the concentration of serotonin. The limit of detection (LOD) of AACDs for 5-HT was 2.24 μM.