Obtaining genetic profiles from biological samples deposited on different materials under varying conditions is essential for human identification and crime scene reconstruction. However, bloodstains are often degraded by environmental exposure, time, surface type, and cleaning attempts, which may reduce DNA quality and quantity, affecting the recovery of interpretable STR profiles. This study evaluated the feasibility of obtaining genetic profiles from blood samples deposited on various materials such as cotton, knives, wool, wood, silk, and synthetic materials. Three individuals donated blood for the study. Blood from three donors was applied to these surfaces and exposed to simulated crime scene conditions in Peru’s coastal, highland, and jungle regions for one and three months. After 1 month and 3 months, the samples were divided into three groups: unwashed, washed with 3gr of detergent in powder (Sapolio, Peru), and washed with detergent (3gr) plus bleach (5ml). Depending on the sample type, 1 cm² was taken with a scalpel with a sterile blade (cotton, silk, and synthetic material) or with a sterile swab (knife and wood). DNA was extracted from these samples using the Prepfiler Express kit and the AutoMate Express Forensic DNA extraction system (Thermo Fisher Scientific). DNA concentrations in each sample were determined using a Qubit fluorometer. A target input of one nanogram of DNA from each sample was amplified by direct PCR using the Verifiler™ Express PCR Amplification Kit (Life Technologies), following the manufacturer's instructions. Amplified products were detected using the Applied Biosystems™ 3500XL Genetic Analyzer (Life Technologies), according to the manufacturer's recommended protocol. After capillary electrophoresis, the data were imported into GeneMapper® ID-X v1.5 software (Thermo Fisher Scientific, 2015) to generate genetic profiles, which were analyzed according to the manufacturer's recommendations. After one month the unwashed samples yielded concentrations ranging from 0.35ng/ul (knife) to 1.16ng/ul (wood), month the washed samples with detergent yielded concentrations ranging from 1.45ng/ul (cotton) to 8.51ng/ul (silk) and the washed samples with detergent plus bleach yielded concentrations ranging from 1.13ng/ul (cotton) to 8.51ng/ul (silk) . After three months unwashed samples yielded concentrations ranging from 3.64ng/ul (wood) to 4.31ng/ul (knife), washed samples with detergent yielded concentrations ranging from 1.56 ng/ul (wool) to 6.35ng/ul (wool) and washed samples with detergent plus bleach yielded concentrations ranging from 1.75ng/ul (synthetic) to 10.21ng/ul (cotton). The various conditions under which the samples were evaluated did not compromise typing or the generation of genetic profiles.

Authors

• Ana Valverde-Vilcherrez (Facultad de Ciencias Biológicas, Universidad Nacional Mayor de San Marcos, Peru)
• Sonia Guillen Ramirez (Laboratorio de Microbiología Molecular y Biotecnología, Facultad de Ciencias Biológicas, Peru)
• Carlos Neyra-Rivera (Facultad de Ciencias de la Salud, Universidad Tecnológica del Perú, Peru)
• Edgardo Delgado Ramos (Posgrado, Universidad Privada Norbert Wiener, Peru)
• Ericson L. Gutierrez (Universidad San Ignacio de Loyola, Unidad de Investigación para la Generación y Síntesis de Evidencias en Salud, Peru)
• Bruce Budowle (Department of Forensic Medicine, University of Helsinki, Finland)