Goals of biological evidence Goals of biological evidence collectioncollection

• Collect as much sample as possible from a single Collect as much sample as possible from a single source—keep it concentratedsource—keep it concentrated

• Ensure that the sample is not inadvertently mixed Ensure that the sample is not inadvertently mixed with other biological samples—change gloves if with other biological samples—change gloves if contaminatedcontaminated

• Handle the sample in a manner that minimizes Handle the sample in a manner that minimizes deterioration—air-dry quickly (and no heat or deterioration—air-dry quickly (and no heat or sunlight exposure)sunlight exposure)

Further recommendations for Further recommendations for collection of biological evidencecollection of biological evidence

• Handle as little as possible—submit the Handle as little as possible—submit the item with the stain still on ititem with the stain still on it

• If stain is on a large porous surface (e.g., a If stain is on a large porous surface (e.g., a rug) cut out the stain area (plus unstained)rug) cut out the stain area (plus unstained)

• Collect with slightly moistened (with dist. Collect with slightly moistened (with dist. water) cotton swab—keep it concentrated, water) cotton swab—keep it concentrated, and take a control swab tooand take a control swab too

Taking care to avoid Taking care to avoid contaminationcontamination

• Don’t allow one evidence stain to come into Don’t allow one evidence stain to come into contact with other biological samples, including contact with other biological samples, including transfer from tools and glovestransfer from tools and gloves

• Don’t talk or cough over evidence stainsDon’t talk or cough over evidence stains• Collect and package stains separatelyCollect and package stains separately• Clean tools (e.g., tweezers) thoroughly, with Clean tools (e.g., tweezers) thoroughly, with

distilled water stream, dry with tissue, repeatdistilled water stream, dry with tissue, repeat• May use disposable toolsMay use disposable tools

Packaging biological evidencePackaging biological evidence

• Allow stains to air-dry as much as possible before Allow stains to air-dry as much as possible before placing in paper bag or envelope—do not use placing in paper bag or envelope—do not use plasticplastic

• Use separate paper containers for each item and Use separate paper containers for each item and package stains and controls separatelypackage stains and controls separately

• Ensure that the paper container is large enough to Ensure that the paper container is large enough to allow circulation around the evidence itemallow circulation around the evidence item

• For garments, use clean paper to prevent different For garments, use clean paper to prevent different stains from contacting each otherstains from contacting each other

Proper collection and procedures are critical to avoid

Contamination

How else will you detect it and reduce/avoid contamination?

Typically, it looks like a mixture:

A combination of DNA from two/more persons

Contamination at autopsy—teeth from decomposed body

Contamination at autopsy—mixed reference

Contamination at autopsy—resolution

Contamination in the lab

From sample From sample with high with high level of DNAlevel of DNA

To sample To sample with low with low level of DNAlevel of DNA

PCR Product Contamination—the Thousand to One Nightmare

It only takes It only takes a minuscule a minuscule amount of amount of amplified amplified product…product…

……to cause a to cause a typing typing disasterdisaster

Contamination—Prevention

• Sample items one-at-a-time• Separate evidence samples from

reference samples• Use protective gear• Separate work areas with dedicated

equipment

Monitoring for Contamination—Controls ‘R’ Us

Bloodstain (Evidence)

Substrate Control

Reagent Blank—for Evidence

Victim’s Reference Sample

Reagent Blank—for References

Negative Amplification Control

Quality Control Sample

Positive Amplification Control

Summary 1• Screening samples for biological evidence includes both physical (e.g. Screening samples for biological evidence includes both physical (e.g.

alternate light sources) and chemical (presumptive tests) detection alternate light sources) and chemical (presumptive tests) detection methods. methods.

• 3 steps- Visualization, Presumptive testing and Confirmation3 steps- Visualization, Presumptive testing and Confirmation– Blood detection include observation of color, microcrystalline tests, luminol Blood detection include observation of color, microcrystalline tests, luminol

detection, chemical presumptive tests based on hemoglobin's peroxidase-like detection, chemical presumptive tests based on hemoglobin's peroxidase-like activity, antibody species tests, and DNA analysis. activity, antibody species tests, and DNA analysis.

– Semen detection includes observation of fluorescence, Acid phosphatase Semen detection includes observation of fluorescence, Acid phosphatase detection methods, then microscopic examination, P30 testing and DNAdetection methods, then microscopic examination, P30 testing and DNA

– Saliva detection includes microscopic examination, amylase detection and DNASaliva detection includes microscopic examination, amylase detection and DNA

Summary 2

• Safety- In collecting biological evidence, safety is paramount. Safety- In collecting biological evidence, safety is paramount. Wear gloves- away from face- Properly dispose of Wear gloves- away from face- Properly dispose of gloves/wash handsgloves/wash hands

• Collect as much sample as possible - keep it concentrated- not Collect as much sample as possible - keep it concentrated- not inadvertently mixed -change gloves if contaminatedinadvertently mixed -change gloves if contaminated

• Handle the sample in a manner that minimizes deterioration—Handle the sample in a manner that minimizes deterioration—air-dry quickly (and no heat or sunlight exposure)air-dry quickly (and no heat or sunlight exposure)

• Prevent contamination- Prevent contamination- Sample items one-at-a-time- Separate evidence samples from reference samples- Use protective gear- Separate work areas with dedicated equipment- Clean the area, tools and run QC

• Monitor for contamination with controls