NCJ Number
223390
Journal
Journal of Forensic Sciences Volume: 53 Issue: 3 Dated: May 2008 Pages: 632-651
Date Published
May 2008
Length
20 pages
Annotation
This report describes the materials, methods, and results for a newly developed nondisposable tip washing routine designed to prevent cross-contamination in carryover during the automated sample processing of forensic material with the TECAN Genesis RSP 150/8 robotic workstations.
Abstract
A 2-percent sodium hypochlorite wash (one-fifth dilution of the 10.8-percent commercial bleach stock) proved to be the best overall approach for preventing cross-contamination of samples processed with the automated protocol. Steps in the bleach wash do not adversely impact the short tandem repeat (STR) profiles developed from DNA extracted robotically, and they allow for major cost savings by using fixed, nondisposable tips. The testing shows that robotic workstations equipped with fixed pipette tips can be used with confidence under properly designed tip-washing routines in the course of processing casework samples with robotic workstations. Although forensic laboratories process a wide variety of biological evidence, obtaining DNA from soil-contaminated exhibits likely represents the most challenging biological samples. The studies reported in this paper focused on this type of test samples, so as to subject the process to the most critical and aggressive testing. After describing sample preparation, this report profiles sample analysis and preparation for DNA extraction, sample and blank sample layouts for contamination checks, "direct" DNA extraction (protocol I with bead percolations), "direct" DNA extraction (protocol 2 using a TE-Shake unit), "differential" DNA extraction (protocol using a TE-Shake unit), DNA quantification, amplification conditions for DNA extracted from biological samples, amplification conditions for blank samples, and analysis of fluorescently labeled amplification products. 4 tables, 5 figures, and 54 references