Quantifying Cell Proliferation with Colony Assay

Colony formation assays can provide cell proliferation information complement to that of cell growth curve. The cell growth and proliferation ability were analyzed by cell growth curves and colony forming assay, respectively [18] (link). The procedure for the colony assay was performed as previously described [13] (link). In brief, both sham and exposed NHEK (2.0×10³) and HaCaT (5×10²) cells were seeded in a 10 cm petri dish and then placed in the incubator. After 144 h of ELF-EMF exposure, the colonies of each petri dish were washed with PBS and fixed with 3 mL of Carnoy's solution (methanol: acetic acid 3∶1, v/v) for 3 min. Then cells were washed with PBS and fixed in 100% methanol for 30 min; subsequently, they were stained with the KaryoMAX Giemsa Stain Solution (Gibco BRL, Grand Island, NY) for 10 min. Each dish was washed with water and dried overnight at room temperature. A colony was defined as a cluster of more than 50 cells. Three independent experiments were conducted.