I response to the question of Jan Keij as to how to block a
glutaraldehyde fixation. What about using Tris ? It has free amines
which react avidly with all aldehydes. Just replace your phosphate
buffer with a Tris buffer and your glutaraldehyde will become
"neutralized" in a single wash step.
Molecular Probes, Inc. does not offer Tris for sale nor has any
commercial interests in Tris (in case you would wonder).
Martin Poot