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Abstract We reported a novel and readily synthesized fluorescent "turn-on" probe L (Dansyl-Glu-Pro-Gly-Cys) based on dansyl group combine tetrapeptide. The probe L exhibited highly sensitive fluorescent recognition to Cd2+ ions in HEPES buffer solutions (10.0 mM, pH 7.4). The 2:1 binding stoichiometry of L with Cd2+ were determined based on fluorescence titration and the Job's plot investigation. The competitive experiments were found to be highly selective for the Cd2+ ions even in the existence of excess competing metal ions including Zn2+, Pb2+, Hg2+ and Cu2+ ions. The binding constant of the complex L -Cd was calculated to be 5.18 × 1010 M−2, and showed great affinity compared to other probes. In addition, the detection limit of the probe L for Cd2+ ions was calculated to be 45 nM, which presented a pronounced sensitivity toward Cd2+ ions. Most importantly, the probe L had wide range of pH and good biocompatibility, and were successfully applied to selectively detected Cd2+ ions within pH range of 7–12 and bioimaging studies in live cells. Graphical Abstract Unlabelled Image Highlights • A novel fluorescent peptide-based probe (L) was synthesized. • L exhibited exclusively selective fluorescent "turn-on" response toward Cd2+ ions. • L displayed high sensitivity for Cd(II) with a low detection limit of 45 nM. • L could serve as a potential probe to detect Cd2+ ions in living cells. [ABSTRACT FROM AUTHOR]

• A new peptide-based fluorescent probe DCH was synthesized. • DCH exhibited high sensitivity to Zn2+, with detection limits of 30.49 nM. • DCH was utilized for detecting Zn2+ in two real samples with high reliability. • DCH was low toxicity and could be used to monitor Zn2+ in two living cells. Zinc (Zn2+) ions play a very important role in the environment and organisms, and it is of great significance to realize the high sensitivity and selectivity detection of Zn2+ ions. Herein, a new peptide-based fluorescent probe named DCH was rationally designed and synthesized by solid phase peptide synthesis with Fmoc chemistry. DCH exhibited excellent fluorescent "turn-on" responding to Zn2+ with highly selective and exhilaratingly sensitive in aqueous media, with detection limits (LOD) as low as 30.49 nM. ESI-MS, Job's plot curves and fluorescence titration results indicated that the stoichiometric ratio between DCH and Zn2+ was 2:1. DCH could be regenerated by adding EDTA solutions to the complex formed during interaction, and indicated that DCH was promising reversibility probe. Furthermore, DCH has excellent practical application potential through two actual water sample experiments. Importantly, DCH was successfully used in monitor cellular Zn2+ and EDTA in living HK2 cells and SV-HUC-1 cells based on good biocompatibility and exciting low toxicity. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new fluorescent probe DAHK was synthesized based on copper peptide backbone. • DAHK could detect Cu2+ in 100 % aqueous medium with obvious fluorescence quenching. • DAHK-Cu2+ ensemble exhibited fluorescent "off–on" response with H 2 S. • DAHK was successfully used to selectively detect Cu2+ and H 2 S in living cells. • DAHK was successfully applied to sensitively detect Cu2+ and H 2 S in test strips. Copper ions (Cu2+) and hydrogen sulfide (H 2 S) detection is of great significance in environmental monitoring and disease screening. Herein, a novel fluorescent probe (DAHK) was rationally designed and easily synthesized based on a copper peptide backbone labelled a dansyl fluorophore. DAHK exhibited large Stokes shift (210 nm), high sensitivity (38.9 nM) and high selectivity response to Cu2+ ions based on obvious fluorescence quenching in HEPES buffer (10.0 mM, pH 7.4) solutions. In addition, the in situ formed DAHK -Cu2+ ensemble was successfully used as a secondary probe for rapidly and sequentially detected H 2 S via fluorescence "off–on" response, and without interference by a range of other anions. The limit of detection (LOD) for 47.3 nM was determined, which was a much lower value than WHO and EPA guidelines (H 2 S) for drinking water. The reversibility of interaction of DAHK with Cu2+ and H 2 S was monitored using fluorescence emission spectra. Cells imaging experiments exhibited that DAHK had good membrane permeability and excellent low toxicity. Moreover, DAHK was successfully made into fluorescent test strips for visual detection and rapid analysis based on the exciting stability and excellent water solubility. [ABSTRACT FROM AUTHOR]