If you are looking for only activated caspase 3 try the R & D catalogue # AF835.
Steam Ag retreival for 25 min, promary Ab incubation of 1 hour, Dako LSAB+ kit
for secondary and SA-HRP for 15 min each.  Dab for 15 minutes.  This will only
detect activated Caspase 3.

Good luck!
Christine Klein
MD Anderson Cancer center