The forensic biology and serology is one of the crucial discipline in the field of forensic sciences. Generally, the forensic serology deals with the analysis of blood, serum, saliva, semen, hair
and other bodily fluids to establish the relationship of the perpetrator to the crime scene. The major concern of forensic serologists to collect the biological evidence present at the crime scene in an adequate way preventing them from contamination.
Blood is one of the crucial evidences and can be commonly found at the crime scene like murder, vehicular accidents, sexual assaults etc. The forensic serologists must answer the following questions at the time of examining blood, blood stain or smears:
1) Is it blood or not?
2) Is it human blood or originate from any other species?
3) If it’s human blood then how closely it can be related to the particular individual?
The preliminary step to examine whether it’s a blood or not, various colour tests are carried out by specialised forensic at the crime scene.
The phenolphthalein test is based on the haemoglobin pigment present in blood which possess peroxidase like activity. The phenolphthalein reagent and hydrogen peroxidase mixture are applied on the bloodstain, thus causes the formation of deep pink colour. The change in colour indicates the presence of blood.
The luminol test is the most sensitive test to detect bloodstains. The bloodstain shows fluorescence instead of producing colour. The luminol reagent is sprayed on the suspected areas, the emission of light can be viewed and thus bloodstain will produce a faint blue glow.
The confirmatory test is performed in the laboratories to determine whether it’s a human blood or not. One of the confirmatory test for origin of species is precipitin test carried out on bloodstain. The precipitin test involves the reaction of antiserum with the corresponding antigen. Another version of precipitin test is the Gel Diffusion method. The extracted bloodstain antigen and human antiserum is placed at different holes opposite to each other. The line of precipitate forms when antigen and antiserum meet, thus confirming the presence of human blood. The precipitin test gives best result even the blood stain is 10-15 years older.
– Ravshish Kaur Kohli
(M.Sc. -Forensic Science), Amity University