Sometimes forensic labs can find ample DNA in the evidence collected at a crime scene. Other times, investigators are not as fortunate. Evidence samples with low amounts of DNA may not yield a profile that investigators can use to match or exclude potential suspects.

Researchers have a potential solution: direct polymerase chain reaction (PCR). This DNA amplification method allows scientists to add a swab or sample directly to the PCR, which eliminates the loss of DNA that traditionally occurs during DNA extraction and quantification.

Laboratories in the United States already use direct PCR for reference samples where the DNA donor is known, but current federal quality assurance standards keep them from using direct PCR for forensic evidence. The federal standards require all unknown forensic samples to undergo DNA quantification prior to amplification.

Direct PCR Outperformed Standard PCR for Many Trace DNA Items
NIJ-funded researchers, led by Jonathan Davoren of Bode Technology, sought to reassess the current FBI guidelines for processing unknown forensic samples. They also assessed the operational requirements needed to maximize DNA recovery using direct PCR, which produced practical data about trace DNA evidence collection and analysis.

Davoren's team sought to better understand:

• How different types of materials work with the direct PCR process by comparing evidence collection results from a variety of items using direct PCR and standard PCR. (Exhibit 2)
• How well direct PCR works (a) after items have been stored for various periods of time and (b) when items are resampled after their initial analysis, by examining the quality of the DNA profiles produced.

First, researchers collected DNA from11 items and processed them using the standard PCR (extraction, quantification, and amplification) and direct PCR methods (no extraction or quantification). The researchers then assessed the quality of theDNA profile based on whether the profile met the criteria to be uploaded into CODIS (the CODIS eligibility success rate).

The direct PCR method produced higher quality DNA samples than standard PCR for trace DNA found on certain items, such as the plastic slides, polyester, metal tool, handgun grip, wood handle, and foam cup (Exhibit 3). However, the direct PCR method produced lower quality DNA samples than the standard PCR method for other items, including the vinyl shutter, denim, 100% wool, concrete bricks, and cartridge casings (Exhibit 4).

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