1：Experimental Design and Method Selection:

The study designed a fluorescence-based detection method using β-cyclodextrin-modified carbon dots (β-CD-CDs) as nanoprobes. The method leverages host-guest recognition between β-CD and cholic acid (CA), and photoinduced electron transfer (PET) between carbon dots and ferrocenylmethyl trimethylammonium iodide (Fc+). The fluorescence quenching and recovery phases were optimized for CA detection.

2：Sample Selection and Data Sources:

Human serum and urine samples were used. Serum was purchased from Chongqing Manuik Technology Co. Ltd., and urine was sampled from healthy adults. Samples were diluted 100 times without complex pretreatment.

3：List of Experimental Equipment and Materials:

Materials included mono(6-amino-6-deoxy)-β-CD, cholic acid, lithocholic acid, deoxycholic acid, chenodeoxycholic acid, Fc+, MgCl2, NaNO3, NaCl, KCl, urea, glucose, glycine, ascorbic acid, DL-tryptophan, glutathione, DL-tyrosine, EDC HCl, NHS, dialysis bags, phosphate buffer solution (PBS), and ultrapure water. Equipment included LS-55 photoluminescence spectroscope, Cary 300 UV–vis spectrophotometer, Tecnai G2 F20 TEM instrument, and Nicolet 380 FTIR spectrophotometer.

4：Experimental Procedures and Operational Workflow:

Synthesis of N-CDs from fish scales via hydrothermal treatment; synthesis of β-CD-CD nanoprobes via covalent bonding using EDC and NHS; construction of β-CD-CD-Fc+ probes by mixing β-CD-CDs, Fc+, and PBS, followed by addition of CA; optimization of pH, Fc+ concentration, and incubation times; fluorescence measurement under excitation at 340 nm and emission at 420 nm.

5：Data Analysis Methods:

Fluorescence intensity ratios (F/F0-1) were used to quantify CA concentration. Linear calibration curves were established for CA concentrations 0–1 μmol·L?1 and 1–650 μmol·L?1. Detection limit was calculated as LOD = 3s/k, where s is standard deviation and k is slope. Recovery rates were calculated for spiked samples.