Alkaline phosphatase-fast red, a new fluorescent label. Application in double labelling for cell cycle analysis.

We have observed that the red reaction product of alkaline phosphatase immuno-conjugates and certain substrate preparations produces a brilliant red fluorescence that is visible by fluorescence microscopy using both fluorescein and rhodamine filter combinations. This provides a level of sensitivity greater than that obtained with other commonly used red fluorochromes or by inspection of the reaction product under bright field illumination. Of particular value, the reaction product is unaffected by the denaturing conditions required for the detection of incorporated nuclear BrdU with FITC conjugated anti-BrdU antibody and provides a simple and robust method for the simultaneous detection of cell proliferation and cell surface markers.