CLPEX Chat Board

I have heard two different descriptions of using Fluorescein to enhance bloody fingerprints. One is that Fluorescein is comparable to other reagents that enhance bloody prints and the other is that Flruorscein causes blurring of the ridge lines regardless of the carrier it is dissolved in.

Can anyone speak to the blurring issue?


Thanks,

Mike French
mike.french@metrokc.gov

Fluorescein is not the best choice to enhance bloody fingerprints by causing the blood to fluoresce. It is great for safety vs. luminol in detecting fine amounts of blood that is not impression evidence.

The problem with the use of fluorescein for blood impression evidence is being able to hold edge detail of the impression. Fluorescein oxidizes rapidly when it dries which causes extreme backgroud fluorescence. A commercial thickener is added to assist in retaining moisture and delaying oxidation. The problem from my research, is that the thickener is problematic in the extraction of DNA.

If Flourescein is used without the thickener it causes the blood to run as it is dissipated into the substrate. The thickener minimized this, however it is not a blood fixative.

Merbromin and Leuco Crystal violet both contain 5-sulfosalicylic acid (Aldrich 24700-6) which is an instantaneous fixative in their formulations. They have no adverse effect on DNA. Refer the below article.
http://www.latent-prints.com/images/Imp ... %20PCR.pdf

Both fluoresce stronly at 532nm and holds the edge detail well.

The below article and images demonstrate this.
http://www.latent-prints.com/cac_blood.htm
http://www.latent-prints.com/images/WEB ... /frame.htm

Not being a chemist, I assume there must be a valid reason that this fixative is not included in fluorescein formulations. I understand that an accurate ph in the fluorescein is very important for it to work and 5-sulfosalicylic acid may have adverse effects.

Dusty Clark

We are currently in the process of validating several blood processing techniques. We were not happy with flourescein as a development medium in comparison to other processes available. Its recovery rate of quality prints was poor. It's a two-step process and has a short shelf life.

About fifteen years ago I started using tetramthylbenzidine. I know it's not the safest chemical out there, it has practically no shelf life, and it's a pain in the butt to make. But when I really need to get the possible ridge detail at the scene of a serious crime, I haven't found anything that works as well. In the past fifteen years I've experimented with Amido Black, Coomasie Blue, Leucomalachite Green, LeucoCrystal Violet, Hungarian Red and o-Tolidine. If I'm processing the scene of a commercial B&E, I'll use the Leuco Crystal Violet, but if I'm processing a homicide, I'll use TMB.