Lecture 4 - Serology/Biological Evidence

Question 1

One issue with prints is that you have to match finger to finger.

Answer 1

The article used AI to solve this issue. Tracked similarities across different fingers that are unique to individuals and then trained the AI to match fingers regardless of which finger you have.

Question 1

Biological evidence

Answer 1

chemical compounds or other
material derived from a living organism

Question 2

Biological Evidence (2)

Answer 2

30 Years Ago, this would only apply to human tissue. Has now expanded into micro-organisms (bacteria, viruses) and animals (wildlife forensics)

Question 3

Two conventional areas for analyzing human biological evidence

Answer 3

Serology and DNA Analysis

Question 4

Serology

Answer 4

Detection and/or identification
of bodily fluids on evidence

Question 5

DNA Analysis

Answer 5

Determination of DNA
profile from that body fluid

Question 6

bodily fluids relevant to forensic investigations

Answer 6

blood, saliva, semen, vaginal tissue, sweat, skin, urine/fecal matter

Question 7

Serological Tests (2)

Answer 7

Presumptive/Confirmatory

Question 8

Presumptive Test

Answer 8

Establishes the possibility that a
specific body fluid is present

These are:
Fast (secs or mins)
-Simple (not many steps)
-Low sensitivity (high sample requirement)
-Prone to false result
-ex: light source, spray, no really involved chemistry

Question 9

Confirmatory Test

Answer 9

Verifies and/or identifies a
specific body fluid is present

-generally slower, more work, more expensive
-few or none false results if done correctly
-holds more weight in court
-more definitive

Question 10

False +

Answer 10

Test result indicates that a body fluid is present
when it is not present

Question 11

False -

Answer 11

Test result indicates that no body fluid is present when it is present (maybe you didn’t spray the entire area)

Question 12

ALS (P or C)

Answer 12

Presumptive

Question 13

ALS explanation

Answer 13

Not very specific for which fluid is present. Can have a lot of false (+)s.

Question 14

Presumptive tests (continued)

Answer 14

They are great tools at the scene. They can help rule out areas where bodily fluid is not present to cut down the area being searched or scrutinized. It can also help figure out what happened. It helps figure out which bodily fluids are present and where they are.

Question 15

Blood

Answer 15

• made up of 1 WBC for every 600-700 RBCs
• WBC has DNA not RBC (DNA analysis targets WBC)
  -Function of blood: provide immune response - fight infection.

Question 16

Red blood cells are the target for some serology tests because they are the biggest constituent. It still indicates blood, even if you can’t get DNA.

Answer 16

Blood has hemoglobin (reduced iron - iron(II) ) this is the crux of most of the presumptive tests of blood. They try to detect the reduced iron in the middle of the hemoglobin complex.

Question 17

Fe in hemoglobin basis for Luminol test (presumptive)

Answer 17

The presence of the reduced iron and the catalyst cleaves the NH-NH bond and replaces it with oxygens. This allows for resonance and delocalized electrons, which leads to fluorescence. Shows up blue.

BUT - many other substances cause fluorescence. Bleach, urine, feces.

Question 18

Luminol is most common but other methods target the iron in compounds (3 P) (3 C)

Answer 18

P: Fluorescein, Phenolphthalein, Tetramethylbenzidine

C: Hematrace, Ouchterlony double diffusion, Teichmann

Question 19

Fluorescein

Answer 19

super aromatic compound and then the presence of iron plus the base catalyst cleaves the ether bond, replacing it with a carboxylic acid and creates a very EN group, changes the pi bond structure and causes it to fluoresce. This shows as yellowish orange in the presence of blood.

Question 20

Phenolphthalein

Answer 20

the presence of hemoglobin will actually convert this structure will rearrange the double bonds in the structure. colorless to bright pink in presence of hemoglobin.

Question 21

Tetramethylbenzidine

Answer 21

yellow to dark blue. Hemoglobin and hydrogen peroxide changes the pi bond structure so now there’s a double bond between the aromatics.

Question 22

Blood Confirmatory Tests

Answer 22

Many are based on antigens.

Question 23

Hematrace Cards

Answer 23

Differentiate between blood from different species. The card contains human blood already. The sample is added. If the precipitation reaction is seen, it mean the blood is human. This is because antigens and antibodies are specific to a species. Only human antigens will react with the human antibodies.

Question 24

Ouchterlony double diffusion

Answer 24

the Unknown sample goes in the center of a gelatin or agar plate. The center is surrounded by antibodies from different species. Once sample is added, it diffuses out from the center and interacts with the antibodies it matches. Whatever it matches is where a precipitation reaction will be seen.

Question 25

Teichmann

Answer 25

One of the first confirmatory Tests - a microchemical reaction where the presence of hemoglobin will create a mineral precipitate only in the presence of blood

Question 26

Saliva is important…(2)

Answer 26

SA cases that only involve saliva. also: saliva has so much DNA - important for other crimes.

Question 27

Saliva: Primary Components

Answer 27

-Water, mucus
-Various digestive enzymes including
lipases (fat) and amylase (breaks down starches)
-Salts and electrolytes (Na+, Cl-, HCO3-)

Question 28

What do many presumptive tests for saliva target? Why?

Answer 28

Amylase. It is very abundant in saliva. And it’s relatively stable. Can still get a nice sample after a couple months to a year.

Question 29

Tests for Saliva.

Answer 29

Starch-Iodide, Phadebas Reagent

Question 30

Starch-Iodide

Answer 30

When in the presence of iodine, starch
produces a blue solution. If amylase is present, starch is broken down and solution becomes
colorless. Proteins from blood, semen
can also react with iodine
(i.e., false positives)

Question 31

Phadebas Reagent

Answer 31

Usually done on fabric. Spray fabric with reagent. Outline places where saliva may be. Transfer paper is added and saturated with development solution. Paper is taken off to look for color change and to see if corresponds to these suspected areas of saliva deposition. Can also be done in solution. Blue to purple color change. Amylase cleaves bond between starch and the dye, producing a color change.

Question 32

Urine

Answer 32

may be important for sexual assault, harassment, or
mischief cases - demonstrates that someone was in a certain place

Question 33

Urine Primary Components

Answer 33

Water
-Urea, creatinine, nitrogen waste products
- Nucleated Epithelial cells (low concentration) (Shed from urinary tract - chance for DNA profile)
-typically low pH, acidic due to nitrogen waste

Question 34

Urine Tests

Answer 34

Most of the tests that are described for detecting urine usually involve protein or enzyme like urease breaking down urea (into NH3 and CO2, detecting the pH change with strips.

Question 35

Urine Test Usefulness

Answer 35

Lot of false positives because many things can create a change in pH. Also, many times urine is found on fabrics which decreases the sensitivity and it’s more difficult to test as it’s embedded into porous substances. Urine also has very low DNA yield. so low chance of DNA profile.

Question 36

Two applications of serological tests.

Answer 36

Historically, determine where DNA is to isolate and test DNA for the best chance at a profile.
However, more and more recently, the focus has shifted to where this DNA has come from and how it got there. Spitting, SA, blood.