The Comet Assay: An Overview of Techniques

The comet assay is a gel electrophoresis method that is used to visualize and measure DNA strand breaks in individual cells using microscopy. In its simplest form, cells are embedded in agarose on a microscope slide, immersed in a lysis solution to remove lipids and proteins, and exposed to a weak electric field to attract broken, negatively-charged DNA towards the anode. After electrophoresis, DNA is stained using a fluorescent dye, and viewed using a fluorescence microscope. Individual images can then be digitized and analyzed for informative properties such as the distance the DNA has migrated and the percent of DNA that has migrated. These features give an indication of the number of strand breaks present in the cell.