Luminol

  As we well know that the investigation of blood stains (forensic hematology) continues to occupy a preferential place in Criminalistics, since, frequently, clothes stained with blood during a violent act are washed to try to eliminate the traces. On the other hand, the spectacular advance in research technology on DNA analysis by PCR has endowed criminology with the possibility of studying minimal evidence that, with other methods, it would be impossible to analyze. This type of sample poses a greater difficulty in detecting the stain. In this article we will analyze the sensitivity of luminol to find invisible blood stains; On these spots that are trying to extract and amplify DNA, the results indicate that luminol is very effective in detecting invisible signs. In addition, it is necessary to point out that there is no interference of the reagent in the subsequent extraction and amplification of the DNA.

WHAT IS FLUORESCENCE?

It is the phenomenon by which a substance emits visible light, when irradiated with light, of a shorter wavelength than that absorbed.

WHAT IS PHOSFORESCENCE?

It is the same phenomenon as fluorescence, but the emission of light occurs slowly.

WHAT IS LUMINOL?

It is a substance that, when oxidized in a basic medium, emits light. The oxidant can be H2O2, ClNa, perborate and others.

Luminol is a chemical that glows with a bluish light when it comes in contact with blood. It even reacts with multi-year traces of blood. An ultrasensitive chemical, it can detect blood at one portion per million. In simple terms, this means that if there is even one drop of blood in 999,999 drops of water, the luminol will glow. Luminol is a very sensitive reagent that allows the search and location of blood spots. Due to the application method, it is very useful when large areas are to be surveyed. Furthermore, it has already been proven that its application on (visible) blood stains does not prevent DNA analysis by PCR.

HOW DOES LUMINOL HELP SOLVE CRIMES?

The victims of bloody, violent crimes cannot disappear without a trace which is the basic assumption on which crime scene investigators operate. Not how hard the killer tries to clean up the blood and dispose of the body, some telltale blood traces will remain. Tiny blood particles can cling to most surfaces for years at a time, without ever being considered.

Luminol is effective in revealing these traces. There is a chemical reaction between various chemicals and hemoglobin (a protein in the blood that carries oxygen), that produces light. There is a breakdown of the molecules, which then change to form different molecules. In the chemical reaction of luminol, the original molecules (reactant) have more energy than the new molecules (products). The extra light is discarded by the molecules in the form of light photons. This phenomenon is known as chemiluminescence.

The luminol helped provide clues as to how events may have unfolded or the kind of weapon used. For example, the blood splatter patterns from a blunt object versus a sharp knife will be different. Sometimes, the bloody shoe prints give a lot of clues about the assailant's movements after the attack. Luminol can also lead researchers to discover new evidence. For example, if there is a positive reaction to luminol sprayed on a carpet, then removing the rug can reveal blood-soaked floorboards.

THE INTENSITY OF BRIGHTNESS AND ITS DURATION IN THE EMISSION OF LUMINOL

The temperature, the pH, the catalyst and the same concentration of the luminol will influence the light that is obtained to be more dimmer and the duration of the emission. Although there are several methods to detect blood stains, the application of luminol is interesting because it is a very sensitive test, which allows it to be used in the detection of stains that have been previously washed. The reaction will be catalyzed by the hemoglobin contained in the blood.

APPLICATION AND EFFECTS OF LUMINOL:

An application of this oxidation of luminol is used by specialists to look for clues in cases of homicides, to discover an eventual presence of human blood stains at the scene of a crime, producing luminescence when applied in places where there was blood, even if it has been washed or if the place where it was found has been repainted. Luminescence is produced by applying ultraviolet light to the area suspected of being covered with blood.

Luminol is typically used at a crime scene where the killing is suspected to have happened but there is no trace