CLPEX Chat Board

We are re-examining our SOPs regarding blood print development and would like some clarification on some issues.

There are many references regarding "fixing" blood with either methanol or heat before processing with certain stains. Why does the stain need to be fixed?

Second, there is a wide range of "fix" times and temperatures in supporting literature. Why? We previously had used halogen lamps at a crime scene to "fix" a stain on a surface, is this sufficient? And naturally because we need to satisfy ASCLD, how can we gauge temperature on the blood-bearing surface to know when enough is enough? We know that some biological stains on slides just need a quick pass over a flame to "fix". We have also seen references to 100 degress Celcius for 1 hour. So what is the deal?

Third, if the stain is using methanol for the carrier does the stain need to be "fixed" with metahnol prior to development?

Thanks for any help.

Patrick Warrick

"Fixing" the blood print tends to bond the proteins to the substrate so they are not so easily washed away by your reagent and the denatured proteins are more receptive to the dyes in the reagent. Your blood print can still be washed away even after fixing so you should still exercise gentle application of your reagent...no sloshing or forceful pouring or spraying!

The older and darker a blood print, in general, the better fixed it will be to the surface. Blood impressions which have just recently dried are more apt to be washed away. The methanol fix is quick and can be done with a gentle immersion for a few minutes or a rinse by wash bottle application. Do not forget though that painted or finished wood surfaces will be damaged by methanol (along with your print!) so do a spot check to determine if this fix is safe to use on your evidence. Many of the blood enhancement reagents have water based formulations that utilize mild acid fixers such as 5-sulphosalicylic acid or citric acid. These would be recommended for surfaces in which methanol can not be used. My experience with "heat" fixes were 100C for 20-30 minutes and I found this to be a less desirable way to bond the print to the surface.

As for crime scene application, if you can find a way to bring the blood impression back to the Lab for enhancement you will be better off. This may require cutting out areas of drywall or floor sections. Some of the "heme" reagents (o-tolidene) are applied without fixing, but usually via a "fine misting" which would limit running of the impression, and the ether in the reagent promotes rapid drying. But if the impression is on a vertical surface more prone to running, you have to use techniques which prevent this such as a blotting technigue (covering with a paper towel and sparingly spraying the paper toweling letting the reagent slowly seep to the surface).
There are a number of excellent papers on the subject by John Fischer (out of Florida) who has done extensive research on blood print enhancement that I recommennd you try to access.