Evaluation of Phadebas Forensic Press test paper as a source of biological material for immunochromatographic testing and DNA analysis

Saliva is commonly found at crime scenes and other biological fluids, such as semen, urine, blood, and fecal matter may be present alongside saliva on an article of clothing, such as underwear. Forensic testing is required to detect saliva in order to corroborate events related to a crime and to identify stains that can be used in DNA analysis. A cross-reactivity study was carried out to determine the specificity of the Phadebas® Forensic Press test for saliva stains. Whole blood, semen, urine, fecal matter, vaginal secretions, condoms, lubricants, vinegar, and PBS were all tested for reactivity with the Phadebas® paper. Only fecal matter and urine demonstrated cross-reactivity within the 60-minute test window. As conservation of sample is a necessity in forensics, a study was carried out to determine if a cutting from Phadebas® paper performs similarly to a cutting from the original sample or stain in immunochromatographic testing with RSID^TM-Saliva. Testing of extracts from fabric cuttings allowed for detection of 1:100 dilutions of saliva, whereas only neat, 1:5 and 1:10 dilutions were able to be detected when using Phadebas® paper extracts. These samples were stained and examined under a microscope to determine if enough nucleated epithelial cells were present for STR analysis. Of the 81 fabric extracts examined, 15 were shown to reach the threshold where either a partial or full STR profile would be expected. In contrast, none of the Phadebas® extracts reached the threshold, indicating that a cutting from the original stain is a more reliable source for DNA analysis. Overall, these results support that the Phadebas® Forensic Press test is useful for detecting latent and diluted saliva stains but should be considered a screening method only due to false positive results observed with urine and fecal matter. Furthermore, using Phadebas® Forensic Press test paper as a source of biological material for immunochromatography or DNA analysis is not as successful as using the stained substrate itself, and should be avoided whenever additional sample is available for direct testing