Assays involve cells being seeded into wells and exposed to the treatment of interest. After treatment the cells are fixed and permeabilised to allow intracellular access of a fluorescently-tagged antibody to label the protein of interest.
A fluorescing stoichiometric DNA probe is normally applied to the cells in each well. The resulting signal is directly proportional to the number of cells and can be used to normalise the protein expression appropriately. DRAQ5™ has become the choice for this.