Detection of touch DNA evidence on swab by SYBR®Green I Nucleic Acid Gel Stain

Abstract

Invisible touch DNA sample is one of the most common sample types received in the DNA laboratory. However, the appearance of DNA from touch sample collection cannot be observed until the DNA detection process is completed. The objective of this study focused on effectiveness of SYBR®Green I Nucleic Acid Gel Stain (SYBR Green I, Invitrogen, USA) using four types of swabs; including cotton, rayon, nylon, and foam swab, for collecting touch DNA from objects. Touch DNA samples were collected from 1 male and 1 female volunteers and stained with 5x SYBR Green I. This study demonstrated 3 experimental designs; including effectiveness, stability and visualizing of touch DNA mockup study. The results showed that the foam swab was the only swab type that could distinguish between touch DNA with and without SYBR Green I fluorescence; therefore, the foam swab was studied in the mockup experiment step and was appropriate for the study of the stability of SYBR Green I stained swab. Furthermore, our results on stability study showed that touch DNA on foam swab stained with 5x SYBR Green I fluorescence immediately faded on Day 1 , but remained until Day 28 in the dark at room temperature. The mockup study using a foam swab that collected touch DNA on objects and stained it with 5x SYBR Green I revealed that SYBR Green I fluorescence was visualized differently from that without touch DNA. These outcomes indicated that SYBR Green I can be used as a stain in the touch DNA screening method on foam swabs for forensic laboratory, which would increase productivity by reducing time and resources cost.