An assessment of DNA extraction methods from blood-stained soil in forensic science

Abstract

In forensic crime scene investigations, biological fluids such as blood are commonly found in soil. However, the analysis of blood-stained soil can be challenging due to the presence of inhibitors which limit the effective extraction and amplification of the deoxyribonucleic acid (DNA) required to produce a reportable DNA profile. There are some extraction methods that have been applied to blood-stained soil in forensic science, but these have produced sporadic results. This research has taken a number of different extraction methods from the fields of ancient DNA and environmental DNA and broken them down into the individual steps of pre-treatment, incubation, separation and purification. These steps were assessed independently then combined into various extraction methods to determine the best technique that can effectively and reliably profile human DNA from blood-stained soil. Testing involved assessment of three extraction buffers, (cetyltrimethylammonium bromide, guanidine thiocyanate, and proteinase K), four pre-treatment methods, (polyvinylpyrrolidone, ethylenediaminetetraacetic acid, hydrochloric acid, and sodium hydroxide), three separation steps, (centrifugation, phenol chloroform, and chloroform) and four purification steps, (size exclusion chromatography, bind elute columns, isopropanol precipitation and silica magnetic beads). The most effective procedure was found to be a polyvinylpyrrolidone pre-treatment with a proteinase K extraction buffer followed by magnetic silica bead purification with or without centrifugation. However, centrifugation separation was found to be equally effective after the pre-treatment step as after the incubation step. Our results shows that most of the current forensic procedures would benefit from the addition of a pre-treatment step prior to processing through the automated DNA profiling pipeline.

Keywords: Blood-stained soil; DNA extraction; DNA profile; Degraded DNA; Forensic soil; Humic acids; Inhibition; Pre-treatment.