A simple protocol to improve touch DNA analysis using direct STR amplification

Traditionally, when processing DNA samples, a multiple-step procedure is followed; after a sample has been collected, DNA is then extracted and quantified before a profile is generated. During the process, valuable DNA can be lost and/or consumed. When processing reference samples, where DNA is usually in abundance, DNA loss may not be a concern for the analysts. However, DNA loss from samples that have minimal amounts of DNA could be detrimental to successful analysis. Touch or contact DNA samples are collected when an individual has handled an object, leaving behind genetic material. Genetic and environmental factors can affect the amount of touch DNA deposited; thus, it is important that as much DNA is retrieved from the surface being sampled and made available for analysis. A new collection method, using Promega's SwabSolution™ as a swab wetting agent, is proposed. In comparison to traditional methods, the new procedure significantly increased both the amount of amplifiable DNA retrieved and the number of alleles amplified and maintained with acceptable peak height ratios of heterozygote loci. The proposed method coupled with direct PCR protocols has shown to be a reliable and effective procedure for the analysis of touch DNA samples across a variety of different surfaces.