Why Blood May Glow in the Dark

By SHILLINGTON, David

Science mimics nature to produce illuminating toys and tools. — —————– Popular television programmes often depict forensic testing at crime scenes where small traces of blood are detected using Luminol. It is used to detect blood (which may be old, dry or in small quantities) and relies on a process known as chemi-luminescence.

The process mimics one used by glow worms and fireflies where chemical energy is converted into light without much heat. The investigators apply the luminol substance to the ground or surface being investigated (in the dark) and wait for the blood luminol mixture to glow.

The chemical formula for the compound responsible for this reaction is relatively simple, containing only carbon, nitrogen, hydrogen and oxygen atoms, although the chemical name is a terrible mouthful! When this compound is placed in a basic solution in the presence of a catalyst such as iron (found in blood) the luminol is oxidised (oxygen atoms replace nitrogen atoms) releasing energy as light. The luminol test is good for following blood trails in crime scene work to determine the movements of injured people. This aids the forensic team in putting together a possible sequence of events.

Audiences at rock concerts may wave “glow sticks” to the music beat. Glow sticks exploit these luminol-type reactions using similar compounds inside a variety of plastic containers to form necklaces, bracelets and tubes. Glow sticks generally contain a peroxide to facilitate oxidation and use other chemicals to change the chemi- luminescent energies and hence their colours. These reactions were discovered nearly 100 years ago.

Another light emitting process involves fluorescence, where ultraviolet light is first absorbed by a chemical compound (the molecules become excited) and then the chemical gives off energy as visible light (fluoresces). Luminol (which is chemiluminescent) and other fluorescent chemicals are commonly used in biology and biochemistry for a multitude of other tests such as chromatography, (a method for separating and sorting chemical substances), immunoassay (measures minute concentrations of biological matter in blood) DNA probes, and DNA fingerprinting. In a western blot, (also known as an immunoblot) specific proteins can be determined in a sample. Here specific antibodies are reacted with the protein and the technique is particularly useful in cancer detection and for immunisation research. This test is commonly used as a quality control check in industry.

Television viewers watching crime scene investigations have also seen simulated results of this test appear as bands on a gel which is often held up to the light in dramatic fashion by the laboratory technicians to confirm a match with the suspect.

ELISA, (enzyme linked iummunosorbent assay ) is another commonly employed technique that relies on fluorescence for protein detection.

The protein produces a coloured compound when the antibody has detected or matched the specific protein after reaction with an enzyme (biological catalyst). The fluorescence is then recorded using digital photography.

Tests using luminol are only a small fraction of the possible tests done on blood at a crime scene. Tests performed on blood in routine or specialised medical settings are numerous and vary considerably in complexity.

Technicians working in the field certainly have to be familiar with a range of analytical techniques in the “detective” work they do.

I am pleased to note that as we approach the end of the academic year, the students who study for the National Diploma in Science at UCOL are familiar with these and the many other useful techniques used in a science laboratory, and that they may have earned some “glowing” results.

* David Shillington is head of the School of Applied Health Sciences at UCOL.

(c) 2007 Evening Standard; Palmerston North, New Zealand. Provided by ProQuest Information and Learning. All rights Reserved.