DNA swabbing has revolutionized crime scene investigation. Now forensic professionals can extract information from even the tiniest of samples of epithelial cells, blood, semen, saliva, urine, bone, and other tissue.
But DNA testing for forensic analysis is only as effective as the sample collection methods. Improper sample collection, transport, and testing can lead to contaminated evidence and potentially invalidated results.
To ensure your forensic swabbing methods pass muster, we recommend you follow the steps outlined in each of these three key stages of effective DNA swab sampling:
We cover best practices for each step in detail below, including the appropriate materials to use, and the preferred precautions and methods for forensic swabbing.
The first step to effective DNA swabbing is careful preparation. You must ensure that your crime scene techs are equipped with the right equipment to do their job well. To start, you should ensure all techs have the right tools for this task.
Contamination of samples can become a huge issue in court—potentially compromising months or even years of detective work with a single stray hair or bead of sweat. That’s why well-fitting personal protective equipment such as gloves, masks, overalls, shoe covers, and hair covers should be employed at all times during DNA swab use and specimen collection.
You should also have a few crime scene evidence collection kits equipped with the necessary tools of your trade. These collection kits are essential for ensuring the rapid collection of evidence necessary to reduce contamination. These kits may include the following:
A full list of crime scene essentials, including a breakdown of the various types of evidence collection kits and their contents, is available from the National Institute of Justice.
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When it’s time for your department to reorder your collection equipment, choose a product made especially for forensic sample collection, with particular capabilities for touch DNA, blood, DNA under fingernails, buccal cells, and more.
According to a study released by the National Criminal Justice Reference Service, swabbing is the preferred sample collection method over taping for recovering DNA. Additionally, swabs do a better job of both collecting and releasing samples than tape, and are also preferable to cuttings as altering evidence in this way may compromise its integrity. However, getting the most accurate results depends upon using the most appropriate swabs for this task.
DNA swabs are critical elements of any crime scene investigation kit. To prevent the risk of cross-contamination that can compromise evidence, forensics investigators must use swabs that are free of human contaminants including DNA, DNase and RNase.
There are two types of DNA swabs used in crime scene investigations:
The most common swabs used for the collection of specimens in crime scene investigations remain cotton swabs. These versatile cotton-tipped applicators are produced in a DNA-controlled environment to reduce the risk of contamination.
Depending on the sample type (blood, saliva, touch DNA, etc.) the swabbing method you employ may vary. Whatever swabbing methods you use, changing gloves and forceps after each item is the easiest way to avoid cross contamination.
There are three popular techniques for swabbing.
For a more comprehensive overview of how to swab for touch DNA, please see our earlier post.
A study conducted by The U.S. National Library of Medicine found that the double swab technique improves the quality of DNA swab profiles.
The California Department of Justice lays out several considerations for swabbing blood and bodily fluids.
The most important aspect of collecting cells is ensuring the swab is completely dry during transport to prevent mold and other bacterial growth.
Traditionally, swabs have been dried and then transported in an envelope or drying box, but in recent years specially designed collection tubes have become increasingly popular for both their convenience and effectiveness in preserving samples.
There are products on the market for DNA testing and forensic evidence collection packaged in resealable dry transport tubes. These products, patented by Puritan, include ID labels in every package.
These self-contained tubes ensure safe transport, and are also designed to fit into traditional test tube racks effectively. Some transport tubes also eliminate roll if laid on a flat surface or clinician's bench. Each tube is fitted with a breathable Tyvek® filter that allows the swab to dry while maintaining the integrity of the sample during transport. Transport tubes are available to hold swabs of five inches or six inches in length.
Many crime scene investigators opt to use a cotton swab that comes complete with its own aerated tip protector for convenient, reliable DNA or evidence collection. The Cap-Shure swab features a reclosable, ventilated cap over the swab that allows investigators to air dry and transport samples without risk of contamination.
Puritan is committed to helping crime scene investigators and forensic scientists get the accuracy upon which they depend. If you have questions about the right tools for your specific task, or want to discuss our customization options, we encourage you to reach out at any time.