As a chemiluminescence reagent, luminol is widely used in blood detection. It was synthesized as early as 1853. Since Albrecht first reported the chemiluminescence reaction of luminol with oxidant in alkaline solution in 1928, it was found for the first time that this compound has a wonderful property, which can emit blue light when it is oxidized.
A few years later, someone thought of using this property to detect blood stains. The blood contains hemoglobin, and the oxygen we breathe in from the air is transported to all parts of the body by this protein. Hemoglobin contains iron, which catalyzes the decomposition of hydrogen peroxide, turning hydrogen peroxide into water and monooxygen, which then oxidizes luminol to make it glow.
When examining bloodstains, luminol reacts with heme, a protein responsible for transporting oxygen in hemoglobin, showing a blue-green fluorescence. This detection method is extremely sensitive. It can detect only one millionth of blood. Even if a small drop of blood drops into a large tank of water, it can be detected. The luminol reaction in criminal investigation, generally speaking, is that at the scene of a murder, as long as blood splashes out and touches any object, No matter what kind of cleaning method is used afterwards, as long as the luminol reagent is sprayed on it and observed in the dark environment, there will be blue and white fluorescence due to fluorescence reaction in the place with blood stains.
The disadvantages of luminol:
1. Luminol fluoresces in the presence of copper, copper containing alloys, 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's time to shine is limited, so we should seize the time to take photos
There are several ways to avoid interference in inspection
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 safest way is to use luminol luminescence method to detect the suspected bloodstain, and then use other methods to determine that it is indeed bloodstain. Moreover, after being treated by luminol, the DNA contained in the bloodstain has not been destroyed, and it can be extracted for identification.
Desheng is an old chemical reagent company specializing in the development and production of blood test reagents. Luminol is one of the most commonly used liquid-phase chemiluminescence reagents because of its simple structure, easy synthesis, good water solubility and high luminescent quantum efficiency.
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