Touch DNA / Trace Biological Stain Visible Collection

Authors:  Song Zhihong, Zhou Xiuzhi

DNA evidence is a powerful tool to help crime solve that each human’s DNA is entirely unique. The advanced and innovative DNA collection technique can improve working efficiency and solve cases in a forensic laboratory. Biological stains (bloodstain, semen stains, urine stains, hair roots, teeth, bone, tissue, etc.) and Touch DNA (shedding skin cells) are the main sources of DNA evidence that could be extracted.

Touch DNA includes DNA from skin cells, which is transferred to objects when touched by hands or other body parts, and trace biological stain deposits in smaller amounts, both are invisible to naked eyes and too tiny amount to develop with traditional forensic lights. However, trace DNA evidence places a key role to determine the suspect in a criminal investigation.

Common sources of DNA evidence that can be extracted at the scene of crime or forensic:

1. Touch DNA: Shedding skin cells, DNA is found within nucleated cells in the human body.
2. Biological stains: Semen stain, bloodstain, urine stain, vaginal fluid stain, perspiration stain, etc. Contain large amounts of nucleated cells and therefore are rich in DNA.
3. Tissue: Body fluids, bone, teeth, etc.

Body tissue or most latent biological stain is easy to identify by the commonly used forensic light sources method, no more recommendations here. 

The most common and traditional trace DNA evidence collection method is invisible sampling, crime scene investigators and laboratories collect cells from a possible deposited area depending on their CSI experience on evidence materials analysis, for the evidence materials with uncertain collection areas rely on general judgment extraction or gridding extraction. 

Trace DNA evidence collecting procedure is very sensitive, there is a greater chance of DNA contamination or transfer and could produce much more complex test results. Therefore, the proper collection is an important step, which is depending on the examiner’s CSI experience and advanced investigation equipment. Nowadays, innovative collection methods are available to locate and collect trace DNA evidence, which is a big improvement over than traditional collection methods, increasing the extraction and detectable efficiency of trace DNA evidence. 

Trace DNA evidence visible collection technique reduces the blind and useless extraction avoids the contamination and mixture. The advanced technique adopts specially developed merged spectrums to excite Touch DNA / trace biological stains fluorescence, and reveal the imaging Touch DNA / trace biological stains under a long working distance microscope objective lens, perform revealed-discriminated-visible Touch DNA / trace biological stains sampling.

General Factors Affecting Touch DNA Yield

1. Individual skin-shedding: Age, gender, skin roughness, sweaty or dry hands, lack of handwashing, frequently touch their body with hands, etc.
2. Contact type: Pressure on object/body, friction force of touch, touch time, etc.
3. Substrate surfaces that deposit Touch DNA / trace biological stains, categorize as permeability, roughness, fluorescence intensity, etc.
4. Permeability: Non-permeable surface, permeable surface, semipermeable surface
5. Roughness: Smooth surface or rough surface
6. Fluorescence intensity (working under the matching of merged spectrums and filter): High fluorescence, weak fluorescence, non-fluorescence.

Touch DNA Imaging on Different Kinds of Substrate Surface

1. Non-permeable, smooth, non-fluorescence: metal, ceramic tile, glass, plastics, painted surface, etc.

• General imaging status: Impressions and DNA left on smooth surface, fluorescent granular skin cells spread overprints if the palm/fingerprints are available.
• Sampling method: cotton swab sampling, separately swab for different impression area.
• Application cases:
  
  
  

2. Non-permeable, rough, non-fluorescence: frosted painted surface, frosted metal, frosted plastic, rock, rubber, etc.

1. General imaging status: no clear palm/finger impressions on rough surface, Visible Touch DNA deposited as gathering areas, fluorescent granular skin cells available for collection.
2. Sampling method: cotton swab sampling.
3. Application cases:
   Visible Touch DNA on frosted al-alloy surface
   Visible Touch DNA on artificial leather
   Visible Touch DNA on leather coat
   Visible Touch DNA on frosted painted surface
   Visible Touch DNA on frosted plastic surface

3. Semi-permeable, rough, non-fluorescence: tree bark, wood stick, stone, concrete block, etc.

• General imaging status: no clear palm/finger impressions on rough surface, Visible Touch DNA deposited as gathering areas, visible fluorescent granular skin cells available for collection.
• Sampling method: cotton swab sampling, scraping or cutting etc.
• Application cases:
  Visible Touch DNA on wood stick surface   
  Visible Touch DNA on stone surface

4. Semi-permeable, smooth, non-fluorescence: white latex painted wall surface etc.

• General imaging status: Impressions and Touch DNA left on a smooth surface, visible fluorescent granular skin cells spread overprints if the palm/fingerprints are available.
• Sampling method: Tape Lift method, separately sampling for different impression areas.
• Application cases:
  
  Visible Touch DNA on white latex painted wall surface.

5. Permeable, rough, weak-fluorescence: clothing, fibers, unbleached paper, Nylon material, nonwoven fabric, etc.

• General imaging status: Visible fluorescent granular skin cells spread over contact surface.
• Sampling method: Tape Lift method or cutting.
• Application cases:
  Visible Touch DNA on Cloth Surface    Visible Touch DNA on Sweater surface
  Visible Touch DNA on Felt Surface     Visible Touch DNA on Meltblown Cloth
  Visible Touch DNA on Nylon Woven Bag Visible Touch DNA on Cotton Thread

6. Permeable, rough, strong-fluorescence: A4 paper, clothing, fibers etc. that contained fluorescent dyes.

• General imaging status: Visible fluorescent granular skin cells spread over contact surface, but are influenced heavily by the fluorescent substrate.
• Sampling method: Tape Lift method or cutting.
• Application cases:
  Visible Touch DNA on A4 paper

7. Non-permeable, rough, strong-fluorescence: mineral, etc. that have a fluorescent response.

• General imaging status: Visible fluorescent granular skin cells spread over contact surface, but are influenced heavily by the fluorescent substrate.
• Sampling method: Cotton swab sampling.
• Application cases:
  Visible Touch DNA on pebble which contained fluorescent response.

8. Non-permeable, smooth, strong-fluorescence: plastic products that contained fluorescence. 

• General imaging status: Visible fluorescent granular skin cells and touch impressions spread over contact surface with oblique light illuminating, influenced heavily by fluorescent substrate with direct illuminating.
• Sampling method: Cotton swab sampling or Tape Lift method.
• Application cases:
  Plastic switch box which contained fluorescer. Direct illuminating
  Visible Touch DNA on plastic switch box which contained fluorescent. Oblique illuminating, 

9. Semi-permeable, smooth, weak-fluorescence: some wood log etc.

• General imaging status: Visible fluorescent granular skin cells and touch impressions spread over contact surface with oblique light illuminating, influenced heavily by fluorescent substrate with direct illuminating.
• Sampling method: Cotton swab sampling or scraping.
• Application cases:
  Visible Touch DNA on wood stick, Direct illuminating
  Visible Touch DNA on wood stick, oblique illuminating

10. Permeable, rough, non-fluorescence: concrete block, porous stone, cinder block etc.

• General imaging status: Visible fluorescent granular skin cells spread over contact surface.
• Sampling method: Cotton swab sampling or scraping.
• Application cases:
  Visible Touch DNA on porous stone
  Visible Touch DNA on concrete block,

11. Semi-permeable, smooth, strong-fluorescence: coated paper with smooth surface etc.

• General imaging status: Visible fluorescent granular skin cells spread over contact surface with oblique light illuminating, influenced heavily by fluorescent substrate with direct illuminating.
• Sampling method: Tape Lift method or cutting
• Application cases:
  Coated paper, Direct illuminating
  Visible Touch DNA on coated paper, oblique light illuminating

12. Trace Biological Stains: semen stain, bloodstain, urine stain, vaginal fluid stain, perspiration stain, etc. 

• Trace Bloodstains: Blood stains can be excited fluorescence on substrates like deep-colored clothing etc. However, it is easy to identify on the light color surface with white light and a microscopic lens.
• Trace Semen stains: Body fluids itself has a strong fluorescence response, the stains are visible as green or white fluorescence.
• Sampling method: Cotton swab sampling, Tape Lift method, or scraping
• Application cases:
  Trace Blood stains on dark color clothing
  Trace Semen stains on dark color clothing    

Trace DNA Evidence Visible Collection Technique — Recommended Sampling Methods

1. Pointed Tip Cotton Swab Sampling: Swab the visible area of trace DNA evidence with little deionized water or sterile water on the cotton tip and avoid saturating the swab, keep collected DNA samples in proper place, it’s the best to do DNA amplification on the same day DNA sample is collected to avoid low testing results. Generally recommended for non-permeable substrates, such as painted surface, metal, stone, etc. hard, non-porous items.
2. Small-size Tape Lift method: The located areas of trace DNA evidence for Touch DNA gathering areas could be sampled with a small-size tape. Generally recommended for permeable/semi-permeable substrates, such as clothing, paper, latex painted walls, etc.
3. Cutting: Cutting the visible area of trace DNA evidence, the method is a priority recommended and generally used for soft items, such as clothing, paper, etc. 
4. Scraping: The located areas of trace DNA evidence could be scraped with a sterile scalpel blade, then swabbing or tape lifting. Generally recommended for non-permeable/semi-permeable substrates, in which the DNA evidence stains are dry and hard, or in the gap/dent, such as stone, wood, metal, latex painted wall, etc.

Trace DNA Evidence Visible Collection Technique — Extraction Procedure

1. Be sure to wear appropriate personal protective equipment: gloves, face mask, hair nets, shoe covers, etc.
2. File the collected evidence materials
3. Clean the Trace DNA Evidence Development Device and other tools with medical tissue with 75% alcohol
4. Place the evidence material in the working area of the device
5. Setting ideal light source and filter according to the evidence substrate, continuously detect evidence material and observe in the computer screen, photographing and sampling once revealed the Touch DNA / trace biological stains.
6. Label the tubes with identifying information, at the same time, diagrammatic drawing, remark and photograph collection area on evidence material carefully and ready for tracing to the source and secondary extraction.

Trace DNA Evidence Visible Collection Technique — Matters to Attention

1. Reduce the contamination and damage by physical contact or retransfer
2. Wear proper personal protective equipment is necessary.
3. Anti-contamination evidence bag is required, reduce collected evidence materials interacting with other objects.
4. Fingerprint brush and reagents are not recommended, which could physically damage DNA evidence and interfere DNA analysis. 
5. Dry the wet evidence materials in the shade and avoid exposure to direct sunlight
6. Separately collect Touch DNA in different trace Touch DNA gathering areas, and then collect scattered Touch DNA with a specific size area (e.g. 1-2cm²).
7. DNA can easily be degraded from exposure to sunlight, temperature, bacteria, mold etc., collect in time.
8. Proper storage of DNA evidence is required (e.g. keep dry). DNA testing result is also influenced by storage time, but in the experiment, even 20-30 year’s DNA evidence with proper storage can have a positive result and solve the case.
9. Human body’s Touch DNA comes with high individual differences, the number of shedding skin cells, the transient touch and subsequent objective element may result in the deposited nucleated cells numbers; the reagents, technique process, sequencers that DNA detection used are closely related to DNA testing results, trained and experienced personnel who are well-versed in the techniques and possess specific domain knowledge are necessary.

Conclusion

Developing and collecting TOUCH DNA / Trace Biological Stains is always a technique challenge in crime investigation, so the aim of this article is to highlight the available VISIBLE sampling technique, and provide recommendations for the collection of potential Touch DNA items and to discuss the potential evidential value and matters need attention. The state-of-the-art visible collection technique performs observation, locating, identifying, and collecting TOUCH DNA, improving the results from DNA evidence, which is a major step forward in the forensic technique field.

References

1. The Forensic Experts Group. https://www.forensicexperts.com.sg/value-trace-evidence
2. How to Swab for Touch DNA Evidence(2019). From: https://blog.puritanmedproducts.com/how-to-swab-for-touch-dna-evidence
3. MBADNACONSULT.Touch DNA Resources. From: MBA DNA CONSULTING,   https://mbadnaconsulting.com/2012/02/10/touch-dna-resources/
4. Valentine, Julie L. Ph.D., RN, CNE, SANE-A, FAAN1; Presler-Jur, Paige MS2; Mills, Heather MSFS3; Miles, Suzanne BS3. Evidence Collection and Analysis for Touch Deoxyribonucleic Acid in Groping and Sexual Assault Cases.From: Journal of Forensic Nursing,  https://journals.lww.com/forensicnursing/Fulltext/2021/06000/Evidence_Collection_and_Analysis_for_Touch.2.aspx
5. Stephen Gustitis, Attorney at Law, Texas.   Touch DNA and Criminal Defense Lawyers. From: https://www.hg.org/legal-articles/touch-dna-and-criminal-defense-lawyers-44900
6. Role of Touch DNA, When No Other Relevant Evidences are Present at Scene of Crime. from： Legal Desire Media and Insights, https://legaldesire.com/role-of-touch-dna-when-no-other-relevant-evidences-are-present-at-scene-of-crime/