The development of fluorescence molecules for the fast and effective detection of L-tryptophan (L-Trp) has attracted a lot of attention because it is an important amino acid for baby growth, nitrogen equilibrium in adults, improving sleep, and mood regulation. A dimedone-phenylalanine-based chiral sensor (SDPA) was synthesized and exhibited a strong fluorescence quenching by Fe3+ and Cu2+ in a water/DMSO (3/7) solution with a detection limit of 2.29 × 10-6 M and 6.37 × 10-6 M, respectively. The factors affecting fluorescence sensings, such as the pH and competing cations, were studied. The sensor can be reused at least five times after being treated with EDTA. The Job plot, ESI-MS spectra, 1H NMR spectra, absorbance, and fluorescence titration experiments were investigated to study the mechanism of SDPA-Fe3+ and SDPA-Cu2+ complexation. The SDPA-Cu2+ complex can detect L-tryptophan and L-cysteine at trace levels by turn-on fluorescence with a detection limit of 9.35 × 10-6 M and 8.86 × 10-6 M, respectively. Moreover, applying the SDPA-Cu2+ complex for quantitative analysis of L-tryptophan in real sleep-improving capsules resulted in good recovery. The L-tryptophan level of the Elining capsule was determined at 190.8 ± 10.5 mg/g (mg L-tryptophan/g medicine), which is close to the announced quantity of 180 mg/g. Besides, the SDPA-Cu2+ complex can selectively detect free L-Try molecules and L-Try residues in proteins.
Keywords: Cu(2+); Cysteine; Fe(3+); Fluorescence; Sensor; Tryptophan.
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