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APO-DIRECT™ Procedure


For Cat. No. 556381, see Technical Data Sheet for methods.


Direct 1


  1. Suspend the cells in 1% (w/v) paraformaldehyde in PBS (pH 7.4) at a concentration of 1-2 x 10 6 cells/ml.
  2. Place the cell suspension on ice for 30-60 minutes.
  3. Centrifuge cells for 5 min at 300 x g and discard the supernatant.
  4. Wash the cells in 5 ml of PBS, then pellet the cells by centrifugation. Repeat the wash and centrifugation.
  5. Resuspend the cell pellet in the residual PBS in the tube by gently vortexing the tube.
  6. Adjust the cell concentration to 1-2 x 10 6 cells/ml in 70% (v/v) ice cold ethanol. Let cells stand for a minumum of 30 minutes on ice or in the freezer. See note below.
  7. Let cells stand for a minimum of 30 min on ice or in the freezer.


Staining Protocol


  1. Resuspend the positive (brown cap) and negative (clear cap) control cells by swirling the vials. Remove 1.0 ml aliquots of the control cell suspensions (~1 x 10 6 cells/ml) and place in 12 x 75 mm centrifuge tubes. Centrifuge the control cell suspensions for 5 min at 300 x g and remove the 70% (v/v) ethanol by aspiration, being careful to not disturb the cell pellet.
  2. Resuspend each tube of control cells with 1.0 ml of Wash Buffer (blue cap) for each tube. Centrifuge as before and remove the supernatant by aspiration.
  3. Repeat the Wash Buffer treatment (step 2).
  4. Resuspend each tube of the control cell pellets in 50 µl of the Staining Solution (prepared as described below).


Staining Solution1 Assay6 Assays12 Assays
Reaction Buffer (green cap)10.00 µl50.00 µl100.00 µl
TdT Enzyme (yellow cap)0.75 µl 4.50 µl9.00 µl
FITC-dUTP (orange cap)8.00 µl 48.00 µl 96.00 µl 
Distilled H2032.00 µl  192.00 µl 284.00 µl 
Total Volume50.75 µl 305.50 µl 609.00 µl 


  1. Incubate the cells in the Staining Solution for 60 min at 37°C. The reaction can also be carried out at RT overnight for the control cells. For test samples, the 60 min incubation time at 37°C may need to be adjusted to longer periods of time.
  2. At the end of the incubation time, add 1.0 ml of Rinse Buffer (red cap) to each tube and centrifuge each tube at 300 x g for 5 min. Remove the supernatant by aspiration.
  3. Repeat the cell rinsing with 1.0 ml of the Rinse Buffer, centrifuge and remove the supernatant by aspiration.
    Note: PI/Rnase treatment is not necessary if cell cycle is not being analyzed (Proceed to step 11).
  4. Resuspend the cell pellet in 1.0 ml of the PI/RNase A solution (amber bottle).
    Note: If the cell density is low, decrease the amount of PI/RNase A solution to 0.3 ml.
  5. Incubate the cells in the dark for 30 min at RT.
  6. Analyze the cells in PI/RNase A solution by flow cytometry.
  7. Analyze the cells by flow cytometry within 3 hr of staining. Cells may begin to deteriorate if left overnight before analysis.