Identification of Forensic Fabrics Using a Portable Raman Spectrometer

Significance of the Topic

The analysis of textile fibers represents a critical component in forensic casework as it can link suspects to crime scenes or exonerate the innocent. Traditional FTIR techniques often face challenges from strong absorption by fabrics or mounting substrates, complicating spectral interpretation. Portable Raman spectroscopy offers non-destructive testing without sample preparation and minimal interference from glass or mounting media, making it highly valuable for rapid on-site and laboratory forensic screening.

Objectives and Study Overview

This study evaluates the capability of a handheld Raman spectrometer to identify six undyed fabric types commonly encountered at crime scenes. By building a spectral library and applying a correlation algorithm, the goal was to determine how reliably each fabric could be distinguished within minutes using a match threshold based on hit quality index values.

Methodology and Overall Approach

A reference library was created from the Raman spectra of six undyed fabrics including diacetate, bleached cotton, polyester, polyamide nylon, acrylic and wool. Unknown test samples were measured and their spectra compared automatically against the library. A hit quality index score of 80 or above was set as the criterion for positive identification, reflecting at least 80 percent spectral correlation to a library entry.

Used Instrumentation

The study utilised the following equipment and software:

• Handheld Raman spectrometer with 1064 nanometer laser excitation and fiber optic probe holder
• Video microscope sampling accessory with 20 times objective, coaxial LED illumination and XYZ adjustment for microsample alignment
• Library creation and material identification software featuring performance tests and custom library management

Key Results and Discussion

Rapid and unambiguous identification was achieved for diacetate, bleached cotton, polyamide and acrylic based on distinct Raman signatures. Polyester and wool spectra were highly similar by overall correlation, but specific protein-related bands detected in wool enabled differentiation. In particular, an amide I band near 1653 per centimeter and a disulfide S-S band at 523 per centimeter serve as markers for animal-derived fibers, confirming wool versus polyester.

Benefits and Practical Applications

The demonstrated method allows forensic practitioners to perform on-site screening of fiber evidence with minimal sample handling. The high selectivity of Raman signatures and rapid library matching reduce analysis time to a few minutes, supporting efficient case workflows in both field and laboratory settings.

Future Trends and Potential Applications

Advances in portable Raman instrumentation are expected to further enhance sensitivity and spectral resolution. Integration of expanded spectral libraries and machine learning algorithms may improve discrimination of complex or mixed fiber samples. Potential extension of the approach to dyed fibers and blends can broaden forensic utility.

Conclusion

Portable 1064 nanometer Raman spectroscopy provides a powerful non-destructive tool for forensic fabric identification. Its ability to deliver rapid, reliable results with minimal interference underscores its practicality for both crime scene investigators and forensic laboratories.

Reference

Li Ling Cho Identification of textile fiber by Raman microspectroscopy J Forensic Science 2007 6 1 55-62