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Published: Fri, 02 Feb 2018
Latest techniques in forensic science
Acid phosphatase activity is significantly greater in semen than in any other bodily fluid and so the colour change reaction should occur more rapidly, however, this is not sufficient to enable discrimination between AP from seminal sources, and AP from vaginal or other sources. Prostate specific antigen is often considered a confirmative test due to the fact that it is almost exclusively produced by the prostate gland. However, note should be taken when looking at PSA levels as an indicator of seminal fluid presence, due to the fact that Laux et al (2008)found there to be a presence of PSA in female ejaculate almost to the same volume of PSA found in human semen. For this reason it should be used in conjunction with microscopic analysis. The issue with microscopic analysis of semen is that the spermatozoa’s presence (at least as a whole body + tail) is dependent on the age of the sample.
Presumptive tests for blood – Kastle-Mayer test is still one of the most commonly used and remains effective for a presumptive test as it can detect the presence of haemoglobin, even at dilutions down to 1×107. A positive test result is indicated by a pink/purple colour change. The stain is first swabbed or blotted with moist filter paper, to this ethanol is added to improve sensitivity of the test, then 1 drop of phenolphthalein which is the colour indicator and then hydrogen peroxide.
Shanan et al (2007) performed various tests using different dilutions of blood and various household products in an attempt to evaluate and compare 6 presumptive tests for blood. The tests evaluated were Luminol, Phenolphthalein, LMG, Hemastix™, Hemident™ and Bluestar©. Post presumptive procedures they also tested the samples for DNA to determine whether or not the tests had damaged or destroyed the DNA. This research found that LMG had the lowest sensitivity of the 6 presumptive tests (1:10,000 – as opposed to 1:10,000,000 for the other 5) and no DNA could be extracted from the sample after being tested with the LMG. With Hemident™, no DNA could be recovered from the sample once it had undergone presumptive testing. This could be due to error in procedure. DNA was not damaged and could be recovered from Luminol, phenolphthalein, Hemastix™ and Bluestar©. As should be done in all scenarios involving the use of these presumptive tests, controls were performed.
Luminol reacts with the iron found in haemoglobin. As only a little of the iron is needed to catalyze the luminescence, luminal can be used to detect trace amounts of blood. It is a process known as chemiluminescence – the generation of electromagnetic radiation as light by the release of energy from a chemical reaction (Quickenden et al 2001). Luminol is not suitable as confirmative proof of the presence of blood as it will react with other iron and copper containing compounds as well as some household products.
As with the entire presumptive test for blood catalogue, this cannot give an indicator of species, serological tests will have to be performed. Hexagon OBTI works using an antibody/antigen reaction. Human haemoglobin reacts with a reagent of anti-human antibodies and blue particles. Hermon et al (2003) validated the use of Hexagon OBTI. They collected various types of blood, tissue and body fluids for testing purposes. The Kastle-Meyer test correctly produced a positive result for all the blood stains; however the Hexagon OBTI only indicated positive results for human bloodstains. Other tests for origin of species include precipitin tests, in which the blood sample is reacted with anti-human antibodies or antisera (Gunn, 2006) If a white line is formed where the 2 samples meet (The blood and the antisera) it is indicative that the blood is human.
Commonly used confirmative tests for blood include the Takeyama test and the Teichmann’s test. Both of these are microcrystalline tests. For both tests, the sample is placed on a microscope slide and covered with a cover slip. The reagent (Takeyama or Teichmanns) is then added over the cover slip and allowed to flow underneath. The slide is then gently heated on a hot plate for around 20 seconds (at 65°C) before being removed and viewed under a microscope. Teichmann’s reagent consists of 100ml glacial acetic acid, 0.1gm KCL, 0.1g KBr, and 0.1g KI. Takeyama reagent consists of, 65ml of distilled water, 20ml pyridine, 10ml 10%NaOH , and 5ml 10% glucose. (These reagent compositions are the standards set by Miller (1969) in their research paper) The appearance of pink hemochromogen crystals when using the Takayama test is indicative of the presence of blood. Brown Ferroprotoprophyrin crystals will form if blood is present using the Teichmann’s.
Techniques for the microscopic analysis of the morphological features have changed very little over the years. The pigment distribution, presence (and relative size) of medulla, cuticular scaling shape etc are all examined when trying to decipher the hairs source (i.e. human or animal). Drug testing from hair samples ia a fairly recent phenomenon, especially in samples belonging to deceased individuals. Mass spectrometry is a commonly used approach as the results can be easily compared to a library of substances (Kintz et al 2005)
A. Gunn. 2003. Essential Forensic Biology. Wiley and sons Limited.
Dalia Hermon ; Moshe Shpitzen ; Carla Oz ; Baruch Glattstein ; Myriam Azoury ; Ron Gafny. 2003. Use of the Hexagon OBTI test for detection of human blood at crime scenes and on items of evidence, part 1: Validation studies and implementation. Journal of Forensic Identification. 53:5 p566-575
P. Kintz , A. Tracqui and P. Mangin. 2005. Detection of drugs in hair for clinical and forensic applications. International journal of legal medicine. 105:1 p1-4
Dale L. Laux, M.S. & Sarah E. Custis (PDF). Forensic Detection of Semen III. Detection of PSA Using Membrane Based Tests: Sensitivity Issues with Regards to the Presence of PSA in Other Body Fluids. Midwestern Association of Forensic Scientists. http://mafs.net/pdf/forensicdetectionsemen3.pdf. Retrieved 2008-05-11.
L. B. Miller. 1969. Hemochromogen crystal formation with minute amounts of blood. Journal of Forensic Science. 9:1-2 P84-86
S.S Tobe, N Watson, and N N Daeid. 2007. Evaluation of 6 presumptive tests for blood. Their specificity, sensitivity and effect on high molecular weight DNA. Journal of Forensic Science. 52:1
T. I. Quickenden and P. D. Cooper. 2001. Increasing specificity of the forensic Luminol test for blood. Luminescence ;16:251-253
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