Detecting and identifying body fluids at crimes scenes provide critical information regarding the event that might have taken place and the individuals who were involved. The location and presence of body fluids, along with the DNA profile obtained, can provide police agencies with an abundance of critical information to help with their investigations.
Unfortunately, the body fluid analysis process can often take a long time. Visualisation technique might be used at the scene of the incident in order to locate body fluids initially, for example using alternative light sources (ALS). It uses various wavelengths of light in order to visualise things such as stains that would otherwise be ambiguous or invisible, and some are even able to show stains that have been covered up with paint or wiped clean. However, using alternative light sources doesn’t usually allow for the differentiation between various body fluids. After potential biofluids are found in-situ, there may be presumptive tests conducted in order to identify possible stains, and after a sample has been collected DNA analysis and confirmatory analysis will often be performed. Unfortunately, there isn’t one single method that is used for analysing all body fluids, and it might be necessary to use multiple techniques as well as a drum pump depending on what kind of biofluid it is.
The most common type of body fluid found at crime scenes that is of interest is undoubtedly blood. Blood is mainly comprised of blood cells and water, along with many metabolites, glucose, hormones, minerals and proteins. Due to blood being obviously important in forensic contexts, various tests have been developed for identifying blood. Presumptive tests might be used initially at a crime scene is order to established whether or not a suspicious stain actually is blood. The presumptive test which is most well-known is perhaps Luminol. It results in the blood having a distinctive blue luminescence, which is based on haemoglobin oxidizing the blood. Fluorescein is another similar test done on the basis of fluorescin being heme-accelerated oxidized into fluorescein, although an alternative light source is required for visualising the change. Phenolphthalein is another well-known presumptive blood test, which is also referred to as Kastle-Meyer. An alkaline solution takes on a pink colour when blood is present. Another very popular presumptive test is Leucomalachite green (LMG), which results in a distinctive change to a green colour when there is heme present in the blood. Along with all of these tests, there are several other immunological blood tests as well that are commercially available, including HemaTrace, ABAcard, and Heme Select. There appears to be an endless amount of presumptive tests that are available for detecting blood, and there are various techniques that may be used in different countries as well as between different police forces. The tests, however, are only presumptive, as suggested by the name, and additional analysis might be necessary in order to confirm a suspected bodily fluid’s identity.
There is an antibody-based method based test called RSID) Rapid Stain Identification), which may be used for confirming the presence of blood which is based on detecting glycophorin A. Also, ELISA (enzyme-linked immunosorbent assays) may be used for identifying blood as well as differentiating between various blood groups. There are certain crystal tests that might be used for confirming the presence of blood, like the Teichman test, based on hematin formation, or the Takayama test, which utilises hemochromogen crystals formation. Further analytic techniques may also be applied for identifying blood, including spectroscopic methods like fluorescence spectroscopy and UV-vis or microscopy for identifying blood cells.
There have been numerous techniques developed for identifying body fluids within forensic contexts, which range for presumptive tests for quick estimations in-situ of a likely identify all the way to confirmation laboratory-based tests. However, the existing techniques do have various problems that are associated with them. The main concern with all of the presumptive test is a lack of specificity since the tests frequently react with various substances so that false positives can be a problem. Some tests are also not especially sensitive, and therefore small body fluid amounts might produce false negatives. Confirmatory and presumption tests, finally, are typically destructive of the sample, which definitely isn’t ideal, especially if there is only a small amount of evidence that is available to begin with.