There is a publication on the subject, namely "A novel assay to measure loss
of plasma membrane asymmetry during apoptosis of adherent cells in culture"
by van Engeland et al. (Cytometry 24:131-139, 1996)
Good luck,
Bert Schutte
Department of Molecular Cell Biology & Genetics
University of Maastricht
Maastricht
The Netherlands
Email: bert.schutte@molcelb.unimaas.nl