HER2-staining of MCF7 and SKBr3. Selective HER2 staining demonstrated in MCF7 (HER2−) and SKBr3 (HER2+) cells. First row: MCF7, from left to right: DAPI counterstain (fluorescent blue), HER2 stained with Liquid Permanent Red (red), and a composite of all channels. Second row: SKBr3, in the corresponding channels. Positive membrane staining was visible in SKBr3 cells only. Additionally, assessment of HER2 staining was also possible using bright-field microscopy, as demonstrated in the lower two rows (third row: MCF7, and fourth row: SKBr3).