1：Experimental Design and Method Selection

The study involved the preparation of NaYF4:Yb,Tm/ZnO/CdS composite film electrode by pulsed laser deposition (PLD) to utilize the upconversion luminescence of NaYF4:Yb,Tm nanophosphors under 980 nm laser excitation for AFP detection.

2：Sample Selection and Data Sources

Alpha-fetoprotein (AFP) samples were used to test the biosensor's sensitivity and detection limit. The materials for the composite film were selected based on their ability to absorb specific wavelengths of light emitted by the upconversion nanophosphors.

3：List of Experimental Equipment and Materials

Bulk NaYF4:Yb,Tm powders, zinc oxide (ZnO) power, cadmium sulfide (CdS) target, chitosan (CS), and other chemicals were used. Equipment included a JEOL JSM-7500 field emission scanning electron microscope (SEM), Rigaku D/max 2550 X-ray diffractometer, and a CHI660D electrochemical analyzer.

4：Experimental Procedures and Operational Workflow

The composite film was prepared by PLD, followed by the immobilization of anti-AFP antibody on the electrode surface using chitosan. The biosensor's performance was evaluated through photocurrent measurements under 980 nm laser excitation.

5：Data Analysis Methods

Photocurrent responses were analyzed to determine the biosensor's sensitivity and detection limit for AFP. Electrochemical impedance spectroscopy (EIS) was used to analyze the biosensor construction process.