Identification of Microplastics with Portable Raman Microscopy

Significance of the Topic

Plastic pollution, especially microplastics in marine environments, poses serious ecological and health risks. Reliable identification of microplastics is essential for monitoring sources, distribution, and potential biological impacts.

Objectives and Study Overview

This study evaluates the application of portable Raman microscopy for rapid, in-situ identification of microplastics recovered from estuarine surface waters. It aims to demonstrate the method's accuracy in polymer classification and highlight its suitability for field use.

Methodology and Instrumentation

Water samples from Delaware Bay were collected via plankton net tows, preserved, size-fractionated, and treated to isolate microplastics. Particles (300–5000 µm) were manually sorted by morphology under stereomicroscopy. Raman spectra were acquired using an i-Raman® EX portable system with 1064 nm excitation to suppress fluorescence. A video microscope with 50× objective enabled precise targeting. Spectral matching against a reference library was performed using BWSpec® and BWID® software.

Used Instrumentation

• i-Raman® EX portable Raman system (1064 nm, InGaAs detector)
• Raman Video Micro-Sampling System with 20× objective and coaxial LED illumination
• Video microscope setup (50× magnification, 9.15 mm working distance)

Key Results and Discussion

The method identified polyethylene, polypropylene, and polystyrene in various microplastic morphologies (fragments, fibers, beads). Hit Quality Indices (HQIs) exceeded 95 for most samples, confirming robust matching. Challenges included black particles with strong absorption and delicate fibers prone to laser-induced damage at higher power. Additional spectral features revealed colorant pigments, providing forensic insight into sample origins.

Advantages and Practical Applications

• Rapid, non-destructive polymer identification on-site
• Suppression of fluorescence via near-infrared excitation
• High spatial resolution for small particles (<100 µm)
• Ability to detect additives and pigments for source tracking

Future Trends and Potential Applications

Advancements in portable spectrometer sensitivity and expanded spectral libraries will further enhance field-based microplastic analysis. Integration with automated image analysis and machine learning promises higher throughput and improved classification. The approach may extend to soil, air, and biotic tissues for comprehensive environmental monitoring.

Conclusion

Portable Raman microscopy with 1064 nm excitation provides a reliable, field-capable solution for microplastic identification. Its non-destructive nature, minimal sample preparation, and strong spectral specificity support its adoption in routine environmental assessment.

References

1. Law, K.L. et al. Annual Review of Marine Science, 9, 205–229 (2017).
2. Galloway, T.S., Cole, M., Lewis, C. Nat. Ecol. Evol., 1 (2017).
3. Jambeck, J.R. et al. Science, 347, 768–771 (2015).
4. Hale, R.C. et al. J. Geophys. Res. Oceans, 125 (2020).
5. Clark, J.R. et al. Front. Ecol. Environ., 14, 317–324 (2016).
6. Vermeiren, P. et al. Mar. Pollut. Bull., 113, 7–16 (2016).
7. Cohen, J.H. et al. Environ. Sci. Technol., 53, 14204–14211 (2019).
8. Masura, J. et al. NOAA Technical Memorandum NOS-OR&R-48 (2015).