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 (CVav% = 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 (CVav% = 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.
Keywords: copper detection; copper poisoning; copper-dependent diseases; fluorescence quenching; serotonin; serotonin-derived fluorophore; urine analysis.