Development of a modified p-dimethylaminocinnamaldehyde solution for touch DNA analysis and its application to STR analysis.

We developed an acid-free p-dimethylaminocinnamaldehyde (DMAC) solution containing silicone oil that was suitable for spraying on clothing for analysis of biological samples such as touch DNA. We investigated the effect of this solution and irradiation with blue light emitting diode (LED) light on short tandem repeat (STR) analysis. To examine the effect of adding acid to the DMAC solution on visualizing biological samples, saliva sample was deposited on T-shirt. The T-shirt was sprayed with acid-added DMAC or acid-free DMAC solution and left for 2 h before irradiation with the blue LED light. We observed no differences between the fluorescence intensities achieved with these two solutions. To examine the effect of acid addition to the DMAC solution on STR analysis, sweat samples were smeared on glass slides and dried. The slides were sprayed with acid-added or acid-free DMAC solution and irradiated with the blue LED light. Samples were collected from the slides with swabs, and DNA was extracted from each sample using a PrepFiler Express™ Forensic DNA Extraction Kit and quantified using a Human DNA quantification kit (Takara RR281). The extracted DNA was amplified using an AmpFℓSTR Identifiler Plus PCR Amplification Kit for STR typing. We found that addition of acid to DMAC had little effect on DNA contained in the biological samples and STR analysis. To investigate whether DMAC could be used to visualize biological samples on clothes, saliva, sweat, and finger and palm prints were deposited on separate T-shirts. Biological samples were treated with DMAC and observed after 2 h, 1, 2, or 3 days under the blue LED. All biological samples were visualized and emitted fluorescence after 2 h. To examine the effects of the DMAC solution and LED irradiation on STR analysis, including DNA extraction, quantification, and STR typing, saliva and sweat were smeared on glass slides and dried. Touch DNA samples were deposited on glass slides directly. The slides were then sprayed with DMAC solution, sprayed with DMAC solution and irradiated with the blue LED, or left untreated. Samples were collected from the slides with swabs, and DNA was extracted, quantified, and amplified using the above kits. These results suggest that the DMAC solution and blue LED light will have no adverse effects on STR analysis. Therefore, this method will be very useful for touch DNA analysis in forensic investigations.