1. Forensic Analysis of Blood using Luminol

2. Luminol
Redox reaction with oxygen in the presence of catalyst produces a bright blue glow.
Used in forensic analysis for detection of blood
Iron in hemoglobin acts as catalyst
Other common catalysts
Biological: copper and cyanide
Laboratory: potassium ferricyanide
Luminol
5-Amino-2,3-dihydro- 1,4-phthalazinedione

3. Chemiluminescence Chemical reaction produces an excited state compound
Excited state compound passes through intermediate
Decays to ground state
Emits a photon

4. Chemical Reactions
Luminol must be activated by hydroxide salt forming a dianion:
In the presence of iron (catalyst), hydrogen peroxide decomposes to form oxygen:
2H2O2 O2 + 2H2O
-2 OH-
2 H20 +
Luminol
Dianion
Dianion Fe

5. Triplet Dianion (excited state)
The dianion reacts with oxygen producing the unstable organic peroxide intermediate:
This intermediate decomposes from higher energy states to the ground state, emitting a photon.
+O2
Dianion
Triplet Dianion (excited state)
Intersystem
Crossing hv
Triplet Dianion
(excited state)
Singlet Dianion
(excited state)
Ground State
*intersystem crossing is radiationless transition between different states of spin multiplicity

6. Chemiluminescence Triplet Dianion Singlet Dianion Energy Ground State
As shown by the red dot, Luminol is excited into the triplet dianion state chemically. Through intersystem crossing, the molecule is able to transtion into the singlet dianion state of the same energy. Finally, the molecule fluoresces from the singlet dianion state to the ground state dianion emitting a photon of energy hv.

7. Advantages & Disadvantages
Fast
Easy
Disadvantages:
Fluoresces in the presence of other compounds, including bleach & horseradish
Can prevent other testing
Possible carcinogen

8. Application
Luminol can be used in a healthcare setting for contamination assessment
P.W.M. Bergervoet*, N. van Riessen, F.W. Sebens, W.C. van der Zwet. J of Hospital Infection. 68 (2008):