2.5. Analysis of Cell Apoptosis

The cell apoptosis analysis was performed using the Annexin V-FITC Apoptosis Detection Kit (Nanjing Vazyme Biotech Co., Ltd., A211-01/02, Nanjing, China), following the manufacturer’s protocol. Briefly, GC-1 cells were seeded in six-well plates at a density of 1.8 × 10⁵ cells/mL per well and incubated separately with the Ni NP suspension at concentrations of 0, 25, 50, and 100 μg/mL. Subsequently, the cells were trypsinized with 0.25% trypsin (without EDTA), washed three times with pre-chilled phosphate-buffered saline, and centrifugated at 1500 rpm for 5 min. The cells were resuspended in 500 μL binding buffer and stained with 5 μL FITC and 5 μL PI in the dark for 15 min. Finally, cell apoptosis was detected by flow cytometry (FACSCalibur, BD Biosciences, San Jose, CA, USA) and then analyzed using the FlowJo_V10 software.