UC Davis - Cutting Comparison

Objective: Determine how much touch DNA the M-Vac can recover from cotton fabric compared to the common collection technique of cutting a small portion of the material.  This study will help determine which method, M-Vac or cuttings, will yield the most touch DNA from fabric.

Methods: Female volunteer wears a cotton shirt for 8 hours.  Upper chest region of the shirt is divided into 3 regions, center, right and left.  Male volunteer grabs region 2 for 45 seconds.  Male volunteer runs until perspiring then grabs region 3 for 45 seconds.  A cutting is taken from each region and each region is collected using the M-Vac.  Control collections were taken with both methods from the shirt prior to the experiment.

Extraction/Analysis: Extract the DNA using the QIAmp^® DNA Investigator Kit (Qiagen).  DNA quantification was done with Quantifiler Duo^® Kit (ABI). DNA amplification was done with AmpFISTER^® Identifiler^® PCR Kit and YSTR Kit (ABI).

Results:  The M-Vac collected significantly more DNA material than was obtained through cutting with P values ranging from 0.0011 to 0.0079.

Conclusions: Touch DNA is typically not visible to the naked eye, even with the use of ALS (Alternative Light Source).  Therefore, using a collection technique that only covers a small area can limit the DNA recovered.  Cuttings are typically restricted to a 1 cm2 fragment, whereas the M-Vac can collect one sample from a much larger area.  Compared to cuttings, the M-Vac collects more touch DNA because it is capable of covering a much larger surface area.  In some trials, the cutting resulted in little or no DNA; however, the M-Vac is capable of collecting touch DNA.  Regardless of the collection method used, more touch DNA is recovered if the contributor has sweaty hands.