Luminol is a chemical that emits light through chemiluminescence when exposed to certain metals like iron found in blood. When sprayed at a crime scene, luminol can detect bloodstains even if attempts were made to clean them up due to hemoglobin's stability. The oxidation reaction of luminol gains oxygen while losing nitrogen and hydrogen, producing an excited state compound that emits blue light as electrons return to the ground state. However, luminol may also react with other substances like bleach and can destroy genetic evidence in blood, so it is best used as a last resort to support physical evidence at a crime scene.

1. Chemiluminescence in Blood Stain Detection

2. In the media…

3. Blood and other body fluids found at the scene of a crime may give important physical evidence in three ways Blood typing analysis can be used to eliminate whole groups of people as suspects. Shape, position, size or intensity of a bloodstain may support a particular sequence of events. Occurrence of a blood strain in a certain place, e.g. on a weapon may substantiate an account of a crime. It is thus obviously important to be able to identify a particular stain as blood or not, or maybe even to reveal "hidden" bloodstains on dark materials or where attempts have been made to wash the blood away.

4. What is Luminol? Luminolis an organic compound When oxidized, emits light — a phenomenon known as chemiluminescence Chemiluminscence is a property in which a substance is undergoing a chemical reaction and releasing energy in the form of lights Example: firefly and glow sticks Produce chemical that, when exposed to other substances that catalyze the reaction, produce a glow Formula: C8H7N3O2 Discovered in the late 19th century

6. Scientists modified the method of using luminol over the years When placed in alkaline or basic solution (hydrogen peroxide or permanganate), luminol emits a faint glow When luminol is exposed to certain trace metals (copper, manganese, or iron), the metals act as a catalyst to create a stronger, more efficient reaction Stronger glow

7. What produces the glow? Oxidation Reaction When Exposed to alkaline conditions, Nitrogen atoms in Luminol are replaced with oxygen atoms. This causes release of nitrogen gas Energy generated from this reaction is released in the form of light Research showed that hydrogen peroxide served as the best base for luminal and Cobalt was the best metal catalyst for a strong reaction…however, there is another metal that was most significant to forensic scientists when using luminol…

8. The Luminol Reaction (* indicates an electronically excited state) Suspected bloodstain on cloth? Reveal by spraying with luminol in the dark

11. When the molecule 2 is formed, it is in an excited (higher energy) electronic state, and sheds its "extra" energy by emitting a photon of light (hn), allowing the molecule to go to its ground state form (3).

12. In aqueous solutions, the luminol oxidation is catalyzed by the presence of a metal ion, such as iron(II) or copper(II).

14. Forensic Application of Luminol 1930s: German forensic scientist discovered luminol could be used to test for presence of blood Blood is naturally alkaline (pH is slightly basic…7.35 to 7.45) Blood contains Hemoglobin, responsible for carrying oxygen throughout the body Hemoglobin contains the trace metal Iron (Fe) Iron in hemoglobin catches oxygen atoms so RBC can carry them throughout the body Iron in blood acts as a catalyst, oxidizing luminol and creating a faint glow

15. Luminol at the Crime Scene Investigators spray a luminol/hydrogen peroxide solution at a scene They examine the scene for a reaction of components of blood with the luminol Even if an attempt is made to clean blood from the scene, traces will still be visible and react with the luminol Hemoglobin is very stable Luminol can be used to detect blood at a scene that is several years old

16. Drawbacks of Luminol Forensics in the media Luminol may react with other chemicals and produce a glow, not just blood Reacts with cleaning reagents, such as bleach What can this tell us about a crime scene Luminol can also destroy genetic evidence in blood Makes DNA testing less efficient or impossible Should not be used where there is little blood evidence present You don’t want to further dilute the blood with luminol or compromise the little genetic evidence available Luminol often is used as a last resort to support trace evidence from the scene