Identification of Forensic Fabrics Using a Portable Raman Spectrometer

Importance of the Topic

Forensic fiber analysis plays a critical role in criminal investigations by providing evidence that can link suspects to crime scenes or exonerate individuals. Raman spectroscopy offers non-destructive, high-selectivity chemical fingerprinting directly on fibers without sample preparation, overcoming limitations of FTIR due to strong absorption by textiles or mounting media.

Objectives and Study Overview

This work evaluates the performance of a portable 1064 nm Raman spectrometer for rapid identification of six undyed textile fibers: diacetate, bleached cotton, polyester, polyamide (nylon), acrylic, and wool. A spectral library and Hit Quality Index (HQI) matching approach are used to assess identification accuracy under field-ready conditions.

Applied Methodology and Instrumentation

Sample Preparation and Measurement

• Six undyed fabrics tested without chemical pretreatment.
• Fibers mounted on glass slides or examined free-standing under a microscope accessory.
• Spectra acquired in situ via a portable Raman probe.

Instrumentation

• B&W Tek i-Raman EX portable Raman spectrometer, 1064 nm excitation.
• Fiber-optic probe holder for flexible access to sample surfaces.
• Raman Video Micro-Sampling System with 20× objective, coaxial LED illumination, and XYZ adjustments for targeting microsamples.
• BWID Standard Raman ID software for library creation, spectral matching, and HQI calculation.

Main Results and Discussion

Unambiguous Identification

• Diacetate, bleached cotton, polyamide, and acrylic fibers yielded distinct Raman signatures and were correctly identified with HQI ≥ 80.
• Overlaid spectra demonstrate clear separation among these four fiber types.

Challenge with Polyester vs. Wool

• Polyester and wool spectra exhibit similar general profiles, complicating HQI-only differentiation.
• Presence of protein markers in wool: an amide I band at ~1653 cm⁻¹ (cysteine backbone) and a disulfide S–S band at ~523 cm⁻¹.
• These two peaks allow reliable distinction of wool from polyester despite high spectral resemblance.

Benefits and Practical Applications

Raman fiber analysis offers:

• Rapid on-site identification within minutes, facilitating timely investigative decisions.
• Non-destructive testing preserving valuable trace evidence.
• Minimal or no sample preparation, reducing handling errors.
• High chemical specificity enabling discrimination of closely related polymers.

The portable setup suits both crime scene deployments and routine laboratory workflows.

Future Trends and Potential Applications

Emerging directions include:

• Expansion of spectral libraries covering dyed, blended, and treated textiles.
• Integration of chemometric and machine learning algorithms for automated classification and anomaly detection.
• Development of multi-modal handheld devices combining Raman with complementary optical or mass spectrometric probes.
• Cloud-based data sharing to support collaborative forensic databases and real-time identification across agencies.

Conclusion

The study demonstrates that a portable 1064 nm Raman spectrometer combined with targeted spectral libraries enables rapid, reliable, and non-destructive identification of common forensic fibers. Key protein-related bands extend the method’s discriminative power to challenging cases such as wool versus polyester.

Reference

• Cho L-L. Identification of textile fiber by Raman microspectroscopy. J Forensic Sci. 2007;6(1):55–62.