A label-free fluorescent peptide probe for sensitive and selective determination of copper and sulfide ions in aqueous systems.

A label free fluorescent peptide probe (HDSGWEVHH) was used for Cu 2+ and S 2- determination in aqueous solution. Our results demonstrated that HDSGWEVHH is highly selective and sensitive for monitoring free Cu 2+ concentration via quenching of the probe fluorescence upon Cu 2+ binding. The mechanism of the complexation is investigated with Cyclic Voltammetry (CV), 1 H nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) spectroscopy and computational techniques. Theoretical calculation results indicated the binding ratio of the probe to Cu 2+ is 2 : 1 and the binding constant was obtained as 1.72 × 10 8 M -1 . Cu 2+ concentration can be detected with the detection limit of 16 nM. Free Cu 2+ concentration released from the metallothionein-Cu complex at different pH values was detected. Cu 2+ concentration in real water and tea samples was also detected, and the results were consistent with the ones monitored by atomic absorption spectrometer. Because of the exceedingly small K sp value of CuS (1.27 × 10 -36 ), S 2- can sequester Cu 2+ from HDSGWEVHH to restore the tryptophan (W) fluorescence. Thus the HDSGWEVHH-Cu 2+ complex can also be used for S 2- detection. The S 2- concentrations can be monitored with a detection limit of 19 nM. The assay is also amenable to measurement of S 2- concentration in pure water samples. Thus the probe designed herein is sensitive, label free, low cost, and environmentally friendly for Cu 2+ and S 2- determination in aqueous solutions.