Sample collection and preservation play a crucial role in whether or not viable information will be obtained from a biological sample.When collecting evidentiary samples, the goal is to maximize the potential for successful short tandem repeat (STR) analysis by recovering the greatest amount of useable DNA as possible without causing contamination. Swabbing is a common method for collecting evidentiary samples [1]. Many variables, such as the swab type, substrate upon which the biological material is deposited, swabbing method, and preservation techniques, can affect the amount and quality of DNA present at the time of analysis [2,3]. Standard swabs used for collecting biological samples for forensic casework include different fibers that are wound around a shaft [4].These fibers are typically either cotton, polyester, rayon, or other types such as padded swabs (a sleeve, usually foam, attached to a shaft) and flocked swabs (fibers, usually nylon, attached to a shaft rather than wound around) [4,5]. A 2014 study reported that
There is significant interest in the use of miRNA analysis for forensic body fluid identification. Demonstrated co-extraction and detection in DNA extracts could make the use of miRNAs a more streamlined molecular body fluid identification method than other RNA-based methods. We previously reported a reverse transcription-quantitative PCR (RT-qPCR) panel of eight miRNAs that classified venous and menstrual blood, feces, urine, saliva, semen, and vaginal secretions using a quadratic discriminant analysis (QDA) model with 93% accuracy in RNA extracts. Herein, miRNA expression in DNA extracts from 50 donors of each body fluid were tested using the model. Initially, a classification rate of 87% was obtained, which increased to 92% when three additional miRNAs were added. Body fluid identification was found to be reliable across population samples of mixed ages, ethnicities, and sex, with 72–98% of the unknown samples classifying correctly. The model was then tested against compromised samples and over biological cycles, where classification accuracy varied, depending on the body fluid. In conclusion, we demonstrated the ability to classify body fluids using miRNA expression from DNA extracts, eliminating the need for RNA extraction, greatly reducing evidentiary sample consumption and processing time in forensic laboratories, but acknowledge that compromised semen and saliva samples can fail to classify properly, and mixed sample classification remains untested and may have limitations.
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