We often see on TV that when the police find evidence of crime, the ground is clean. How do they know where there is blood? And through what to test the bloodstain? We have to mention our little detective Lumino.
Luminosity of Luminol
Luminol, also known as luminol, is a kind of chemiluminescent molecule. It is easily soluble in lye, soluble in dilute acid, almost insoluble in water, and hardly soluble in alcohol. The suitable fluorescence wavelength was 425nm (chemiluminescence was detected in 60 mm K2S2O8, 100 mm K2CO3, pH 11.5). In the presence of hydrogen peroxide, it can be transformed into excited state aminophthalic acid, which emits strong fluorescence. It is a kind of blood that can not be observed by naked eyes at the scene of crime, and can show a very small amount of blood form (occult blood reaction). The chemical name is 5-amino-benzoylhydrazide.
At room temperature is a blue crystal or pale yellow powder, is a relatively stable synthetic organic compounds. The chemical formula is c8h7n3o2. At the same time, luminol is a kind of strong acid, which can stimulate eyes, skin and respiratory tract. Hemoglobin contains iron, which can catalyze the decomposition of hydrogen peroxide, turning hydrogen peroxide into water and monooxygen, which then oxidizes luminol to make it glow. Therefore, luminol is widely used in criminal investigation, bioengineering, chemical tracing and other fields.
In forensic medicine, luminol reagent uses the reagent to identify blood. Even if the blood stains are wiped, the heme in the blood will still remain. When luminol reagent is sprayed on the heme, it will oxidize with reactive oxygen species and release blue purple fluorescence. It is an organic substance used to identify blood. In biology, luminol is used to detect the presence of copper, iron and other substances in cells.
But it also has some disadvantages
1. Luminol fluoresces in the presence of iron, ferroalloys, horseradish or some bleaching agents. So if the crime scene is completely bleached, luminol's fluorescence will strongly mask the presence of any blood stains.
2. Luminol can detect a small amount of blood in animal blood and urine, so if there is urine or animal blood in the room to be tested, the test results will be biased.
3. Luminol reacts with excreta and emits the same light as blood.
4. Luminol may interfere with other tests, but luminol does not interfere with DNA extraction.
5. Luminol needs to be used in a dark environment, otherwise the fluorescence is difficult to identify.
6. Luminol luminescent time is limited, we should seize the time to take photos and record.
How can we avoid interference
1、 Let the site dry for a few days, the interference of bleach will disappear, and the bloodstain can make luminol glow even after many years.
2、 Use a compound that can inhibit the interference of hypochlorite. It's obvious that antioxidants should not be used because they will inhibit the reaction of blood stains with luminol. According to the chemical structure of hypochlorous acid, such as the chlorine atom it contains, suitable inhibitors have been found. The safe way is to use luminol luminescence method to detect the suspected blood substance, and then use other methods to determine that it is indeed blood.
Moreover, it was found that after the bloodstain was treated with luminol, the DNA contained in it was not destroyed, and it could be extracted for identification.
Through the above, it is not difficult to guess how those bloodstains were detected.
Since its establishment in 2005, Desheng company has been committed to the development and production of luminescent reagents, blood collection additives, biological buffers, etc., with rich experience.
