Crime scene investigators have long known that fibers found at a crime scene can provide valuable clues to help find the individual who committed the crime, especially when “fiber transfer” occurs during the commission of a crime. A wide variety of techniques are used to compare fibers, including visual comparison of characteristics, such as material, color, diameter, and cross-sectional shape. Fibers can also be compared through fluorescence, refractive index and an optical property known as birefringence.
The research effort was split between chemists in the university’s textile chemistry program and engineers and computer scientists in the school’s precision engineering center. According to the researchers, the textile focus was to find the optimum extraction conditions for hundreds of fabrics and dye combinations. The engineers and computer scientists worked to develop an automated device that could extract 10 nanograms of the dye from a minute fabric sample.” Once the dye was extracted it was analyzed in a time-of-flight mass spectrometer in less than 10 minutes.
The researchers noted that the 2009 National Academy of Sciences Report on Forensic Science called for improved quantitative analysis of trace evidence and said their research did just that. Through the development of an automated micro-fluidic dye extraction system and the use of statistics-based methodologies, the researchers said their work moved toward the elimination of subjective assessment by analysts.
The ability to do statistical error calculations is critical, they noted, because “one of the long-standing challenges of trace evidence analysis of dyed fibers is the paucity of statistical rigor in comparing a standard and unknown fiber. Statistical rigor can only be achieved via objective methods that are repeatable, reproducible, and enable comparison to a comprehensive database of dyes.”
They concluded by saying: “The methods developed in this project are a step towards identification of dyes within fibers and with minimal loss of fiber that could enable objective comparison of dyed fibers, and ultimately as a statistical error calculation that could be meaningful in the courtroom.”
About This Article
The research described in this article was funded by NIJ cooperative agreement number 2011-DN-BX-K561, awarded to the North Carolina State University Precision Engineering Center. This article is based on the grantee report: “Microfluidic System for Automated Dye Molecule Extraction and Detection for Forensic Fiber Identification”(pdf, 172 pages).