1：Experimental Design and Method Selection:

The probe L was designed to mimic natural protein binding sites, utilizing FRET effects for ratiometric detection. Solid phase peptide synthesis was employed for synthesis, and fluorescence measurements were conducted in aqueous buffer.

2：Sample Selection and Data Sources:

The probe L was synthesized and characterized. Metal ion solutions were prepared from perchlorate salts. HeLa cells were used for cytotoxicity and imaging studies.

3：List of Experimental Equipment and Materials:

Instruments included HPLC with Vydac C18 column, ESI-MS spectrometer (Bruker Daltonics Esquire 6000), spectrofluorometer (Cary eclipse), lifetime spectrometer (Edinburgh Instrument FSL920), pH meter (pHS-3E), confocal microscope (Zeiss LSM 710). Materials included Fmoc-protected amino acids, dansyl chloride, Rink Amide resin, solvents, and cell culture reagents.

4：0). Materials included Fmoc-protected amino acids, dansyl chloride, Rink Amide resin, solvents, and cell culture reagents. Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Synthesis involved SPPS, dansylation, cleavage, purification, and characterization. Fluorescence measurements were done in HEPES buffer at pH 7.4. Cytotoxicity assays involved incubating HeLa cells with L and measuring survival. Cell imaging was performed after incubating cells with L and Cd2+.

5：Cytotoxicity assays involved incubating HeLa cells with L and measuring survival. Cell imaging was performed after incubating cells with L and Cd2+. Data Analysis Methods:

5. Data Analysis Methods: Fluorescence spectra were analyzed for intensity changes. Binding constants were determined using non-linear curve fitting. Detection limits were calculated as 3σ/k. Theoretical calculations used Sybyl 6.9 and VMD for structure optimization.