The Comparison of Four DNA Extraction Techniques From Blood for Forensic Application




Otto, Jennifer Blake


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The results of the phenolphthalein sensitivity study indicate that dilutions of blood down to a 1:1,000 level can be detected with the phenolphthalein presumptive test. Even though this value is not as sensitive as reported by other studies (17), a 1:1,000 level of detection is adequate for day to day use for forensic casework blood presumptive testing. The 1:1,000 dilution level samples were able to amplify and genotype complete or almost complete profiles, so any evidentiary items that give a positive phenolphthalein result should provide an analyst with a good genetic profile. Results from the Quantiblot quantification procedure for the four extraction methods show that the organic extraction with PLG yields the most human DNA out of the four techniques at the 1:10, 1:100, and 1:1,000 blood dilution levels. The organic extraction with PLG tubes also provided the best genetic profiles at the 1:100 and 1:1,000 levels. These results support the use of the organic extraction technique with the addition of the Phase Lock Gel tubes. This method will provide a forensic analyst with the highest yield of human DNA from low copy number blood samples. The organic method provides an analyst with a clean and complete profile at dilution levels lower than the other techniques tested in this project. Although any of the four DNA extraction techniques would provide a high DNA yield and complete genetic profile for known samples with ample DNA, the organic method provides the highest yield of DNA at low levels where sample/evidence consumption may be an issue. When comparing the costs of the four extraction methods per reaction, Chelex 100 is by far the most affordable. One 50g bottle of Chelex 100 resin can be used for approximately 5000 extractions at ~$0.02 per sample. The organic method with PLG tubes is the next affordable, with a price of ~$0.80 per sample. The QIAGEN and DNA IQ kits are more expensive and both cost ~$1.70 per sample. Based on this cost analysis, it may be cost effective to use the Chelex 100 method for known blood samples or evidentiary samples with a large stain present, and the organic method with PLG tubes for any evidentiary blood samples that are small and in limited quantity.