I used normal Rabbit serum in a blocking solution,then attached anti-goat primary antibody, next day used Rabbit anti-goat FITC, second primary antibody was used anti-Rabbit, on 3rd day used secondary antibody swine- anti-Rabbit, confocal microscopy show all the cells were stained for both antibodies like DAPI. How to use normal serum as a blocking solution in double immunofluorescence staining?