A highly sensitive and selective fluorescent “on–off-on” peptide-based probe for sequential detection of Hg2+ and S2− ions: Applications in living cells and zebrafish imaging

[Display omitted] •A novel peptide-based fluorescent probe DNC for sequential detection of Hg2+ and S2− was synthesized.•The detection limits of Hg2+ (8.4 nM) and S2− (5.5 nM) were significantly low.•DNC were successfully applied for sequential detection of Hg2+ and S2− in living cells and zebrafish.•DNC achieved selective and sensitive sensing toward Hg2+ and S2− on test strips.•Smartphone with RGB Color Picker was employed to analyze the different Hg2+ and S2− concentrations. Mercury ions (Hg2+) and sulfur ions (S2−), have caused serious harm to the ecological environment and human health as two kinds of highly toxic pollutants widely used. Therefore, the visual quantitative determination of Hg2+ and S2− is of great significance in the field of environmental monitoring and medical therapy. In this study, a novel fluorescent “on–off-on” peptide-based probe DNC was designed and synthesized using dipeptide (Asn-Cys-NH2) as the raw material via solid phase peptide synthesis (SPPS) technology with Fmoc chemistry. DNC displayed high selectivity in the recognition of Hg2+, and formed non-fluorescence complex (DNC-Hg2+) through 2:1 binding mode. Notably, DNC-Hg2+ complex generated in situ was used as relay response probe for highly selective sequential detection of S2− through reversible formation-separation. DNC achieved highly sensitive detection of Hg2+ and S2− with the detection limits (LODs) of 8.4 nM and 5.5 nM, respectively. Meanwhile, DNC demonstrated feasibility for Hg2+ and S2− detections in two water samples, and the considerable recovery rate was obtained. More importantly, DNC showed excellent water solubility and low toxicity, and was successfully used for consecutive discerning Hg2+ and S2− in test strips, living cells and zebrafish larvae. As an effective visual analysis method in the field, smartphone RGB Color Picker APP realized semi-quantitative detections of Hg2+ and S2− without the need for complicated device.