Forensic Serology Flashcards
What is forensic biology?
The analysis of biological fluids applied to matters concerning the law
What is forensic serology?
The identification of biological stains and body fluids
What is forensic DNA analysis?
The individualization of biological substance to a certain person by DNA profiling
What is the biggest application of forensic biology?
Sexual assault cases
What are the questions of forensic serology and DNA analysis?
Serology:
* What is it?
* Is it blood? Semen? Saliva? Or other?
* Is it human or animal?
DNA analysis:
* Is it human or animal?
* Whose blood/semen/saliva is it?
What are the two most common types of forensic biological specimen found?
Blood and semen
What are the types of biological samples collected?
(three types)
Unknown sample:
* Evidence recovered from scene
Elimination sample:
* victim, family members
* police
* CSI officers
* lab personnel
Reference samples:
* Recovered from suspects
What is the double swab technique?
First swab:
Wet swab to rehydrate cells
Second swab:
Dry swab to collect cells
What are presumptive vs confirmatory tests?
Presumptive test (screening):
* Chemical test which, by production of color or light, indicates the presence of a body fluid
Confirmation test:
* Verifies the presence of a specific compound, (specific type of body fluid)
Using ALS to determine a presumptive test:
(Stain darkening vs fluorescing)
If stain darkens under ALS:
Phenolphthalein (+ ABA hematrace) (blood)
If stain fluoresces under ALS:
Acid Phosphatase
Using acid phosphatase to determine a presumptive test:
Positive:
Christmas tree stain (+ sperm, - P30)
Negative:
Phadebas (saliva)
Best ALS for each fluid type
Semen & Saliva:
Blue light or UV
What are the blood presumptive tests?
Color tests:
* Tetramethylbenzidine (TMB) Test (Hemastix)
* Kastle-Meyer (Phenolphthalein)
Chemiluminescence and Fluorescence Tests:
* Luminol
NOTE: They target Hemoglobin
How does the Tetramethylbenzidine (TMB) Test work?
Uses a reagent strip that will turn blue/green
How does the Kastle-Meyer test work?
- Add a drop of ethanol
- Add a drop of phenolphthalin reagent
- Add 1 drop of hydrogen peroxide
Positive: Turns bright pink
How does the luminol test work?
Reacts with iron in hemoglobin
1. spray chemical mixture
2. if area luminesces, test is positive
Downside: can be destructive to DNA. It is a last resort test!
What is the difference between a 1 phase and a 2 phase test?
1 Phase:
* Sample is added to compound and peroxide at same time
* cannot distinguish between true positive and false positive
* Examples: TMB and luminol
2 Phase:
* Sample and indicator compound are mixed first and then the peroxide is added
* Can indicate when some false positive reactions are occurring
* Example: Phenolphthalein
What presumptive test is most common in a crime lab and why?
Phenolphthalein (Kastle Meyer) test
* Cheap
* Fast
* Not expensive
* 2 phased test
* Safe reagent
* Highly sensitive
* Not human specific
What are the blood confirmation tests?
Microscopic test:
* Takayama crystal assay
Immunochromatographic:
* ABAhematrace (ABAcard)
How does the Takayama test work?
- Drop Takayama reagent on bloodstain
- Heat on hotplate to moderate temp.
- Examine crystal formation under microscope
Red crystal formation = positive
drawbacks: false positives can occur and sample can be destroyed if overheated
Hemochromogen (hemoglobin)
What is a Immunochromatographic test (ABAhematrace)?
- An antibody/antigen reaction
- (looks like a covid test)
- Preferred method in the US
- Target: Hemoglobin
Advantages:
* Sensitive
* Easy
* Human specific
What are the semen presumptive tests?
AP test (acid phosphatase (target))
Brentamine fast blue color detection (most common AP test)
* Acis phosphatase (AP) + fast blue –> purple blue
* Positive reaction within 1 minute = good indication of semen
Brentamine fast blue target = acid phosphatase
What is a semen confirmatory test?
Christmas tree stain:
Nuclear fast red dyes head red
Counter-stain of PIC stains tail green
Steps:
1. Apply nuclear fast red stain for 10 minutes
2. Wash with DI water
3. Apply PIC stain for 15 seconds
4. Wash with ethanol
5. Microscopic examination
What is a secondary semen confirmatory test?
30 (ABA card p30)
* Target: P30 protein
* Semen has a high concentration of P30 compared to other bodily fluids
What is a saliva presumptive test?
Phadebas reagent test:
* Target: Alpha-Amylase
* Blue color molecule released when positive
SALIgAE Saliva test (preferred test):
* Target: Amylase
* Turns yellow when positive
What is a feces presumptive test?
Edelman Test (Schiff’s reagent test):
* Target: urobilinogen
* Combine stain with a chloride mixture and view under UV light
* Glows green when positive
What are the urine presumptive tests?
Uritrace Test:
* Target: Creatinine
Nessler’s Test
* Target: Urea
Jaffe Test
* Target: Creatinine
Immunochromatographic assay
* Target: Tamm Horsfall protein
