A large Stokes shift peptide-based fluorescent probe for Cd²⁺ and Hg²⁺ detection in aqueous solution and its...

Realize the efficient and sensitive detection of cadmium ions (Cd²⁺) and mercury ions (Hg²⁺) based on different response modes is of great significance because their large emissions seriously harm the ecological environment and human health. Herein, a novel peptide-based fluorescent probe named DGGC was synthesized and characterized with satisfactory water solubility (100 % aqueous solution) and significantly large Stokes (230 nm). DGGC exhibited high selectivity and excellent sensitivity towards Cd²⁺ based on fluorescence enhancement response and Hg²⁺ based on fluorescence quenching response. The limit of detections (LODs) for Cd²⁺ and Hg²⁺ were as low as 8.6 nM and 35.1 nM, respectively. The results of fluorescence titration, Job's plot analysis and ESI-HRMS data revealed that DGGC combined with Cd²⁺ and Hg²⁺ in a 2:1 stoichiometric ratio. Additionally, the bioimaging results demonstrated that significant discrimination sensitivity of DGGC for imaging of Cd²⁺ and Hg²⁺ in living cells and zebrafish larvae. In addition, DGGC showed high precision and accuracy in the quantitative analysis of Cd²⁺ and Hg²⁺ in various real samples. Furthermore, DGGC monitored Cd²⁺ and Hg²⁺ contamination on the surface of rice, leaves, kiwifruit and pumpkin under 365 nm UV light using naked eyes. The fluorescence change of DGGC after the addition of Cd²⁺ and Hg²⁺ was used as an INHIBIT logic gate. More significantly, the smartphone colour recognition App was successfully applied to the semi-quantitative detection  of Cd²⁺ and Hg²⁺ without the need for a large instrument.