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_av% = 4% and 3%) and low detection limits (16 ± 1 μg L^-1 and 23 ± 1 μg L^-1). The Cu²⁺ content was also estimated in human urine samples, showing excellent analytical performances (CV_av% = 1%), with a limit of detection of 59 ± 3 μg L^-1 and a limit of quantification of 97 ± 11 μg L^-1, which are below the reference value for a pathological Cu²⁺ 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.