Iron 2 chloride

Bulk black phosphorus crystal (purity > 99.9%) was purchased from Nanjing Muke Nanotechnology (Nanjing, China). Iron (II) chloride and aqueous ammonia were purchased from Shanghai Macklin Biochemical Co., Ltd (Shanghai, China). Doxorubicin hydrochloride, methylene blue and N-methylpyrrolidone (NMP) were purchased from Aladdin (Shanghai, China). DMEM-H, RPMI-1640, fetal bovine serum (FBS), phosphate buffer saline of pH 7.2–7.4 (PBS), trypsin-EDTA, the penicillin-streptomycin solution were purchased from Gibco, Thermo Fisher Scientific. Cell counting kit-8 (CCK-8) was purchased from APExBio Technology (Shanghai, China). H₂O₂ assay kit (S0038) and ROS assay kit (S0033) were purchased from Beyotime Biotechnology (Shanghai, China). Fe₃O₄@PEI nanoparticle was obtained from Xi’an Ruixi Biological Technology (Xi’an, China). Annexin V-FITC/PI apoptosis detection kit and Calcein-AM live-cell staining kit were purchased from Solarbio Life Sciences (Beijing, China).

First, 5 mL of deionized water and both ammonium metatungstate (AMT, (NH₄)₆H₂W₁₂O₄₀·xH₂O, 99.5%, Guangzhou Chemical Reagent Factory, Guangzhou, China) and iron (II) chloride (FeCl₂·4H₂O, Macklin Biochemical Co., Ltd., Shanghai, China) were added to a beaker to prepare a mixture of ammonium metatungstate and iron (II) chloride. Then, solutions with various concentrations of ammonium metatungstate in the solution were made: 0.100 mol/L, 0.125 mol/L, 0.150 mol/L, 0.175 mol/L, and 0.200 mol/L. The concentrations of iron (II) chloride were 0.10 mol/L, 0.15 mol/L, 0.20 mol/L, 0.25 mol/L, and 0.30 mol/L. The precursor solution was produced by sonicating the solutions. Referring to Table 1, the experiment samples are sorted into 25 groups by Taguchi design. The color of the solution changes from yellow to dark brown as the iron (II) chloride concentration rises. Figure 1 shows one example (The 25 samples’ UV-VIS can be found in the Supplementary Materials).