MTT assay

The antitumor activities of SeNPs against different types of cancer cells were determined via MTT (3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide). After counting the cells to be measured, the cells were inoculated into 96-well plates with 10,000 cells per well for 24 h, then the cells were treated with SeNPs at certain concentrations for 24 h. Subsequently, the cells were treated with MTT solution for 3 h, DMSO was added, then the cells were placed for 15 min. Finally, an ELISA microplate reader (DYNEX, USA) was used to measure absorbance at 570 nm (OD value). The standard MTT assay curve was established via the following process: Cells were counted then inoculated into clear cell culture plates at seven concentrations: 1000/well, 2000/well, 4000/well, 8000/well, 16000/well, 32000/well, and 64000/well. They were incubated with MTT reagent at 37 °C for 3 h. After incubation, the cells were treated with DMSO at room temperature for 15 min. Absorbance was measured at OD = 570 nm, and a standard curve was drawn based on the correlation between OD values and cell numbers. The cell number was calculated via the corresponding OD value through the standard curve. The SeNP inhibition rate was calculated via the following equation: inhibition rate = (cell number(control) − cell number(SeNP treatment))/cell number(control) × 100%.