Peptide-based fluorescent and colorimetric dual-functional probe for visual detection of Cu2+, Hg2+ and S2− in 100% aqueous media, living cells and paper test strips

• A novel dual-functional probe FAHK was design and synthesized based on copper peptide backbone. • FAHK showed sequential response towards Cu 2+ /Hg 2+ and S 2− via fluorescent and colorimetric methods. • The detection limit of 37.1 nM for Cu 2+ , 20.8 nM for Hg 2+ and 0.27 μM/0.12 μM for S 2− , respectively. • FAHK has low toxicity and was successfully used to image Cu 2+ , Hg 2+ and S 2− in living cells. • Test strips of FAHK were prepared for rapid and visual detection for Cu 2+ , Hg 2+ and S 2− with naked eye. In this study, a novel peptide-based fluorescent and colorimetric dual-functional probe ( FAHK ) was designed and synthesized by simulating the structure of copper peptide. FAHK exhibited high selectivity and rapid response to Cu 2+ and Hg 2+ with two non-fluorescence ensembles FAHK- Cu 2+ and FAHK- Hg 2+ formation by the 2:1 coordination mode, and the limits of detection for Cu 2+ and Hg 2+ were 37.1 nM and 20.8 nM, respectively. FAHK showed a naked eye colorimetric response for Cu 2+ and Hg 2+ in an aqueous solutions under visible light. As two new promising cascade probes, FAHK- Cu 2+ and FAHK- Hg 2+ ensemble were used for sequential selective recognition of S 2− according to the displacement approach with fluorescence “turn-on” response and colorimetric change, and the limit of detection were 0.27 μM ( FAHK -Cu 2+ ensemble) and 0.12 μM ( FAHK -Hg 2+ ensemble) for S 2− , which were well below the safety level the H 2 S standard in drinking waters (14.8 µM, WHO guidelines). What’ more, in view of low toxicity and biocompatibility, the potential application of FAHK in biological systems was demonstrated via living cells imaging. More importantly, FAHK could also be made into the paper test strips for visual detection of Cu 2+ , Hg 2+ and S 2− with the naked eye under 365 nm UV light and visible light, which suggested that better portability and operation simplicity that is favourable for on-site analysis.