Formaldehyde or ethanol? - (Aug/23/2007 )

HI all,

so my problem is that when i was in grad school, i used 70% ethanol to fix fresh frozen sections. But in my new lab they use 3 % formaldehyde. So my question is does anyone know the chemistry as to how u choose one or the other???

Please help
Pinal

---

Hi Pinal
so..formaldehyde (3% ? strange..usually it's 4%) crosslink proteins between them..so what happen is that you block all the structures and all the protein. Advantages: gives good tissue preservation and very good morphology. Disadvantage: gives a LOT of autofluorescence, so if you use a fluorescence technique (IF, FISH..and so on) you have to use a quenching agent (i.e. Glycine 0.1 M)
Ethanol..extract water and little bit of the lipids and "fix" the protein... Adv: doesn't give autofluorescence (just a little compared to PFA) Disadv: It can ruin the tissue and in any case "shrink" the cells. So if you need precise localization...it's better to use PFA!
Hope this help

---

fulvioce is almost right - the main thing you have to worry about when fixing frozen sections is the unpredictable nature of your primary antibody - some prefer paraformaldehyde (better suited to frozen than formalin or formaldehyde) others prefer alcohols (acetone, methanol, acetone/methanol 50:50 - will work faster than your ethanol)
autofluorescence only really becomes a problem if you have a weak signal from your antibody cos you can always dial it down on the microscope

dom

---