“Fausak had never experienced anything like it. He felt as if he were in a sci- fi movie. Initially, there was the same pale green light. It got greener and brighter. It began to glow. And through its luminosity he could see the trail of blood. The trail was solid, but with streaks in it, as though someone had taken a big wet mop and wrung it out and dragged it along the floor. The length of the bloody trail measured some 55 feet.
“The shimmering glow hung in the air, above Fausak’s knees. It had become so bright that he could see the faces of the forensic men and the chemists.”*
Introduction
The fascinating chemical luminol which produces a bright luminescence when in the presence of the most minute amounts of blood is without a doubt a clear asset to the investigators repertoire. Chemiluminescence occurs when a molecule capable of fluorescing is raised to an excited level during a chemical reaction. Upon its return to the ground state, energy in the form of light is emitted. Only a few molecules are known to emit appreciable amounts of light, and of those, luminol is one of the most outstanding. Much of the early work with luminol occurred in Germany, and consequently, many of the articles require translation. The following text, however, is an attempt to unravel the history of luminol and its use in the detection of blood.
Discovery
A very good historical treatise of luminol’s discovery and mechanism of action appears in Gaensslen’s Sourcebook (1983). Most reports cite A. J. Schmitz as the first to synthesize luminol in 1902; however, a paper by Gill * Maas, Peter. 1990. In A Child’s Name: The Legacy of a Mother’s Murder, New York, New York: Simon and Schuster, p. 112.
states luminol’s discovery to be around 1853. What is certain is that in the early 1900s a chemical having chemiluminescent properties was available and being studied. A better understanding of the chemical’s nature came about in 1928 with Albrecht’s investigations. This study demonstrated that hypochlorites, plant peroxidases and blood greatly enhanced the lumines- cence of the compound with hydrogen peroxide. Albrecht also speculated on a mechanism for the reaction.
In 1934, Huntress and co-workers published an article describing a method of synthesis for the compound and coined the term luminol. Gleu and Pfannstiel (1936) prepared luminol and found that the alkaline solution, with the addition of hydrogen peroxide or sodium peroxide, produced an intense luminescence with hematin. This was independently confirmed by Tamamushi and Akiyama (1938).
Luminol caught the attention of the forensic science world after the exten- sive studies by Specht (1937). Upon the suggestion of Gleu and Pfannstiel, Specht studied fresh and old bloodstains as well as milk, coffee, sperm, saliva, urine, feces, and other body fluids. He tested numerous materials such as wallpaper, fabrics, leather, oils, varnish, wood, grass, leaves, and soil. Interest- ingly, he tested metals (copper, steel, brass, lead, and zinc) and obtained negative results. In the presence of hypochlorite, a weak luminescence was produced. The test was said not to interfere with subsequent crystal or spectral tests, nor with serological tests for species or blood groups. Specht demon- strated the ability to photograph the positive luminol reaction and obtained quality photographs of blood on various substrates including an outdoor setting. Two preparations of luminol were used and were applied as an aerosol with a glass sprayer. Specht found that dried stains produced a more intense chemiluminescence than fresh blood which produced only a “weak glow”. According to Specht, the older the bloodstain, the more intense the reaction, with blood traces a year old or more yielding luminescence. Specht com- mented on the ability to cover large areas of a crime scene or large pieces of evidence quickly with luminol and recommended that luminol be used for medicolegal examinations, believing that it was quite specific for blood.
A very nice paper by Proescher and Moody (1939) confirmed many of Specht’s findings and made three important observations:
• While the test is presumptive, large areas of suspected material can be examined rapidly.
• Dried and decomposed blood gave a stronger and more lasting reaction than fresh blood (three-year old stains gave a brilliant luminescence). • If the luminescence disappears, it may be reproduced by the applica- tion of a fresh luminol-hydrogen peroxide solution; dried bloodstains may thus be made luminescent many times over.
These authors were also among the first to describe parameters for obtaining photographs of the luminescence produced.
McGrath (1942) found the luminol reaction to be rather specific for blood, testing a wide variety of substrates including serum, bile, sputum, pus, seminal stains and feces obtaining no reaction. However, he recommended that the test should not be used as a specific test for blood. He recommended that after its application, which should be kept to a minimum, the stain be photographed and allowed to dry. The stain is then available for all the usual serological analyses. McGrath was unable to detect any differences between stained and unstained samples. Nevertheless, he used a sprayed area with no luminescence as a control for typing purposes.
Luminol’s preparation has changed over the years. Specht (1937) used a mixture of luminol, calcium carbonate and hydrogen peroxide or luminol with sodium peroxide. Proescher and Moody (1939) used sodium carbonate with hydrogen peroxide or sodium peroxide. McGrath (1942) used the meth- ods of both Specht and Proescher and Moody and noted a trace of inherent luminescence of the solution on preparation which could be removed with the addition of indazolon-4-carboxylic acid.
Essentially, the preparation requires luminol, the addition of a base (to make the solution alkaline) and an oxidant. Grodsky et al. (1951) described the preparation of a solution composed of 0.07 g sodium perborate in 10 ml water, to which is added 0.01 g luminol and 0.5 g sodium carbonate.
Weber (1966) published a preparation of luminol consisting of the fol- lowing stock solutions:
• 8 g sodium hydroxide in 500 ml water
• 10 ml 30% hydrogen peroxide in 490 ml water
• 0.354 g luminol in 62.5 ml of 0.4 N sodium hydroxide diluted to 500 ml with water
The test reagent is prepared by mixing 10 ml of each of the above stock solutions with 70 ml of water. This preparation was stated to be an improve- ment over earlier ones in that it reacted well with fresh bloodstains and was more sensitive to dilute blood samples.