Serotonin-Derived Fluorophore: A Novel Fluorescent Biomaterial for Copper Detection in Urine

We took advantage of the fluorescent features of a serotonin-derived fluorophore to develop a simple and low-cost assay for copper in urine. The quenching-based fluorescence assay linearly responds within the concentration range of clinical interest in buffer and in artificial urine, showing very good reproducibility (CV% = 4% and 3%) and low detection limits (16 ± 1 μg L and 23 ± 1 μg L). The Cu content was also estimated in human urine samples, showing excellent analytical performances (CV% = 1%), with a limit of detection of 59 ± 3 μg L and a limit of quantification of 97 ± 11 μg L, which are below the reference value for a pathological Cu concentration. The assay was successfully validated through mass spectrometry measurements. To the best of our knowledge, this is the first example of copper ion detection exploiting the fluorescence quenching of a biopolymer, offering a potential diagnostic tool for copper-dependent diseases.