Supramolecular Cyclodextrin-Enhanced Spectrofluorimetric Determination of Serotonin in Human Urine : Mechanistic...

A sensitive and robust spectrofluorimetric method for the determination of serotonin (5-HT) in human urine was developed based on the inclusion of the neurotransmitter into cyclodextrins (β-CD, HP-β-CD, and HP-γ-CD). The formation of 1:1 host-guest complexes was confirmed by Job's method and double reciprocal analysis. Inclusion of serotonin within cyclodextrin cavities enhanced fluorescence quantum yield through microenvironmental shielding and restriction of non-radiative relaxation pathways by reducing solvent-induced quenching and restricting intramolecular relaxation, without altering the intrinsic excitation or emission wavelengths. The method exhibited excellent linearity over the range of 10-380 ng mL⁻¹, with limits of detection between 0.02 and 0.7 ng mL⁻¹ depending on the cyclodextrin derivative used. Intra- and inter-day precision (RSD) were below 5%, and recoveries in spiked human urine samples ranged from 93% to 101%, demonstrating both accuracy and reproducibility. Among the cyclodextrins tested, HP-β-CD provided the highest sensitivity due to its efficient quantum yield enhancement and solvent shielding effects. Compared to traditional chromatographic methods, this cyclodextrin-assisted spectrofluorimetric approach offers a rapid, cost-effective, and reliable alternative for serotonin quantification in biological matrices. This strategy may be extended to other small aromatic fluorophores or biomarkers for clinical and bioanalytical applications.