Development of a microwave-based extraction for forensic biological samples

Abstract

In this study, a quick microwave-based treatment was developed as a front end for DNA analysis of forensic samples. The effect of microwave treatment is to cause cell disruption which can improve the release of DNA during direct PCR as well as with extraction methods. Exposure to microwave preprocessing improved the quality of rapid genotyping, particularly when used with low level samples. Optimal results were obtained when samples were microwaved at 300W for 40 s, resulting in improved allele detection. Overall, the addition of this simple preprocessing step improves sensitivity and allele recovery for low level DNA samples when combined with expedited DNA analysis workflows. Its main advantages include speed, low cost, compatibility with downstream DNA methods and application to a wide variety of samples.

Keywords: Direct PCR; Forensic analysis; Microwave; Microwave extraction; Rapid DNA; Saliva.

Fig. 1

Overview and speed of the microwave based rapid direct STR process.

Fig. 2

Three different condensation levels with pictures from the condensation test.

Fig. 3

Impact of different buffers on the (A) conductivity and (B) DNA yield from saliva dilutions.

Fig. 4

Microscopy of swabs dipped into saliva and then smeared on the slide. Each column represents a replicate sample. A. Non-Microwave saliva sample B. Microwaved sample for 8 s three times. The number of cells decrease; however, some cell membranes and nuclei remain intact. C. Microwave sample for 30 s (For interpretation, the reader is referred to the web version of this article).

Fig. 5

Based on Neon Bulb Calibration of Microwave, energy positions 1–4 in Row 5 were selected for further experiments.

Fig. 6

Manual Direct STR Electropherogram result of female donor A4 blood sample diluted to 1%. Control replicates were non-microwaved. Treated replicates exposed to 40 s of microwave at 300W. Microwaved and non-microwaved DNA profiles are shown. The boxes above the peaks represents the Peak Height values expressed in RFU (Relative Fluorescence Units). An average increase in peak height of 522% and additional allele recovery shown in red circles were observed.