Advanced IR Spectroscopy Techniques Revolutionize Micro- and Nanoplastics Research

Study of microplastics under a microscope with detailed texture and color variations © AoteBearBro - stock.adobe.com

Microplastics (MPs) and nanoplastics (NPs), collectively referred to as MNPs, have emerged as pervasive pollutants in the environment. Found in marine ecosystems, terrestrial habitats, drinking water, plants, and even within human bodies, these minuscule plastic particles pose potential risks to both ecological and human health (1,2). To address these growing concerns, a recent review published in Analytical Methods explores the advancements in infrared (IR) spectroscopy techniques used for MNP analysis, providing a comprehensive comparison of various instruments and capabilities.

Read More: Microplastics Analysis Using FT-IR

Pioneering IR Spectroscopy Techniques

Fourier-Transform Infrared (FT-IR) Spectroscopy
The review identifies Fourier-transform infrared (FT-IR) spectroscopy as the most widely used technique for MNP analysis. With the integration of focal plane array FT-IR (FPA-FT-IR), the data collection speed has significantly improved, enabling unbiased analysis without manual presorting of particles. This method has become widely used in the automated analysis of MPs (1).

Quantum Cascade Laser Infrared (QCL-IR) Spectroscopy
Quantum cascade laser infrared (QCL-IR) spectroscopy emerges as the second most popular technique. This method allows rapid analysis of plastic particles, making it a valuable tool for researchers dealing with time-sensitive studies (1).

Optical Photothermal Infrared (O-PTIR) Spectroscopy
Optical photothermal infrared (O-PTIR) spectroscopy, known for its submicron spatial resolution, has shown great potential in furnishing detailed analysis of MNPs. This technique offers a higher resolution compared to traditional methods, providing more precise identification and characterization of plastic particles.

Atomic Force Microscopy-Based Infrared (AFM-IR) Spectroscopy
Atomic force microscopy-based infrared (AFM-IR) spectroscopy is highlighted for its ability to analyze MNPs at the nanoscale level. This technique bridges the gap between microscopic and spectroscopic analysis, offering detailed insights into the chemical composition and morphology of nanoplastics.

Comparative Analysis of IR Instruments
The review conducted by Junhao Xie, Aoife Gowen, Wei Xu, and Junli Xu from the School of Biosystems and Food Engineering at University College Dublin, Ireland, and the Department of Life Sciences at Texas A&M University, also presents a detailed comparison of the most advanced IR instruments. Metrics such as substrates/filters, data quality, spatial resolution, data acquisition speed, data processing, and cost were evaluated to provide researchers with a guide for selecting appropriate instrumentation.

Identifying Limitations and Proposing Solutions
While these IR techniques have shown great promise, the review also addresses limitations. For instance, standalone FT-IR spectrometers are suitable for large MPs but require additional microscopes for smaller particles. Similarly, while QCL-IR spectroscopy offers rapid analysis, it may not always achieve the spatial resolution needed for detailed studies. The review proposes recommendations to overcome these limitations, emphasizing the need for continuous advancements in IR spectroscopy instrument technology.

Literature Review Methodology
The literature search involved a comprehensive analysis of articles published within the past three years. Using keywords such as "IR" and "microplastic", the researchers filtered relevant studies from the Scopus database. The search was conducted on April 13, 2023, focusing on articles published in English between 2021 and 2023. This methodology ensured that the review encompassed the latest advancements and applications of IR spectroscopy in MNP research.

Conclusion
The global distribution of MNPs necessitates reliable analytical tools to assess hazards accurately. The review underscores the significance of advanced IR spectroscopic techniques, such as FT-IR, QCL-IR, O-PTIR, and AFM-IR spectroscopy, in providing precise identification and characterization of MNP particles. By understanding the principles, advantages, and limitations of these techniques, researchers can make informed decisions in selecting suitable instrumentation for their studies. This knowledge is crucial for advancing research aimed at mitigating the environmental and health risks associated with MNPs.

References

(1) Xie, J.; Gowen, A.; Xu, W.; Xu, J. Analysing Micro-and Nanoplastics with Cutting- Edge Infrared Spectroscopy Techniques: A Critical Review. Anal. Methods 2024, 16, 2177–2197 DOI: 10.1039/D3AY01808C

(2) Cordeiro, R. D.; Cardoso, V. V.; Carneiro, R. N.; Almeida, C. M. Validation of an FT-IR Microscopy Method for the Monitorization of Microplastics in Water for Human Consumption in Portugal: Lisbon Case Study. Environ. Sci. Pollut. Res. 2024, 1–22. DOI: . 10.1007/s11356-024-33966-8