01 - Forensic Escape Room: Design Your Own Biotech Adventure
Introduction Explore the world of forensic science with these fun and exciting escape room activities! Try forensic blood detection and agarose gel electrophoresis experiments, decipher clues, and solve puzzles. Learn to design your own escape room to have students unravel the evidence and free the innocent. Background Information Excerpts from EDVO-Kits 191 & 130 An abundance of material evidence can be left behind at the scene of a crime. This evidence can include blood on clothing, walls or floors, or even on the potential murder weapon. In some cases a few cells caught under the victim’s nails during a struggle can provide a wealth of information. Evidence can be obtained based on microscopic examination and biotechnological analysis, and then compared to a sample obtained from a person of interest who may have been at the site of the crime. Advances in molecular biology and genetics over the past 30 years have produced a variety of applications that have forever changed forensic science. Human tissue is made up of cells that contain DNA, which can be col- lected from evidence. When combined with the polymerase chain reaction (PCR) and DNA fingerprinting a very small amount of DNA from a biological sample can be analyzed. In many cases the crime can only be solved, and the criminals brought to justice, through the meticulous work of forensic scientists. DETECTION OF BLOOD SPATTERS: Presumptive & Confirmatory Tests The most common presumptive forensic blood test is the Kastle-Meyer test (Box 1). The Kastle-Meyer test uses a compound known as phenolphthalein (pr. fee-nawl-thal-een), which reacts with the iron carried by hemoglobin. First, presumptive blood is gathered on a cotton-tipped swab. The cellular membranes of cells on the swabs are then broken open (lysed) by applying a few drops of 95% ethanol. Phenolphthalin solution is then applied, followed quickly by hydrogen peroxide. If the cotton swab turns pink, it means that there was likely hemoglobin in the sample. BOX 1: Chemistry of the Kastle-Meyer Test The phenolphthalein (C 2 0H 16 O 4 ) used in the Kastle-Meyer test has been reduced, i.e. it has gained electrons, and is actually called phenolphthalin (C 2 0H 14 O 4 ) . The reaction in the Kastle-Meyer test is based on the reac- tion between the iron in hemoglobin and hydrogen peroxide (H 2 O 2 ). The iron in hemoglobin reduces (sup- plies electrons to) the H 2 O 2 , creating water (H 2 O). This reaction depletes the hemoglobin of electrons, which are in turn supplied by phenolphthalin. The oxidation, i.e. the release of electrons, of phenolphthalin turns it back into phenolphthalein, which has a characteristic pink color. Fe 4+ + C 2 0H 14 O 4 + H 2 O 2 → C 2 0H 16 O 4 + H 2 O + Fe 3+ Presumptive tests, such as the Kastle-Meyer, must be confirmed using a test that definitively detects blood. These are known as confirmatory tests. Confirmatory tests are often much more expensive and can take more time than presumptive tests. The most common confirmatory test for blood is the Rapid Stain Identification of Human Blood (RSID). The RSID works similarly to a pregnancy test. The sample is applied to the test strip, and antibodies that recognize blood proteins specifically bind to the sample. If the antibodies bind and the sample is positive for blood, a visible line is shown in the viewing window. Another confirmatory test for blood is ABO blood type testing. Testing for blood groups relies on the precipitation of an antigen-antibody complex, called agglutination. Only blood will produce this agglu- tination, which is why it is classified as a confirmatory blood test. In addition to being a confirmatory test, ABO blood typing is also a faster and more affordable identity test than other analysis techniques such as DNA fingerprinting. Indeed, forensic blood typing serves both as a confirmatory test and provides information about the suspect in the form of their blood type. Even though blood typing cannot point to a specific person as the criminal, it can point to a group of people that share the same blood type or eliminate suspects whose blood type does not match.
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