Using Raman Spectroscopy to Detect Polypropylene Plastics

In a recent study published in Food Chemistry, researchers from Jiangnan University employed a top-down approach to craft micro/nanoparticle (M/NPs) models of polypropylene (PP) particles (1).

Microplastics are tiny plastic particles resulting from the degradation of larger plastics, found widely in nature and impacting both wildlife and humans (1,2). Microplastics are present in marine species, drinking water, and various foods like salt, honey, and seafood, and can also be inhaled (2). Animal studies indicate that once absorbed, microplastics can travel to vital organs, including the liver, spleen, heart, lungs, thymus, reproductive organs, kidneys, and brain (2). Additionally, they can carry pollutants and heavy metals through the food chain. Upon ingestion, microplastics and additives can disrupt biological processes, affecting the endocrine and immune systems, mobility, reproduction, development, and potentially causing cancer (2).

Close up side shot of microplastics lay on people hand. Concept of water pollution and global warming. Climate change idea. Micro plastics concept in food and water or sea | Image Credit: © Deemerwha studio - stock.adobe.com

Polypropylene is the polyolefin most utilized in plastic food packaging (1). As a result, detecting PP particles takes on a greater importance. In their study, researchers Zhilong Yu and Yunfei Xie, both from Jiangnan University, developed and proposed a new method for detecting polypropylene (PP) micro- and nanoparticles.

Unlike most current laboratory studies that rely on man-made polystyrene (PS) spheres, this study was among the first to extensively investigate micrometer- and nanoscale PP plastic particles (1). The research aimed to bridge the gap between laboratory conditions and real-world environments, enhancing the relevance and accuracy of microplastic studies.

To achieve this, the team employed a top-down approach to craft micro/nanoparticle (M/NPs) models of PP particles. By varying solution concentrations and volumes, they synthesized PP particles with sizes ranging from 203 to 2101 nanometers (nm) (1). These particles exhibited negative charges, a characteristic that plays a crucial role in their behavior and interaction with other substances (1).

One of the key components of the study was developing a Raman-based qualitative and quantitative detection method for micro/nano PP particles. Raman spectroscopy, combined with microscopy, was used to measure the particles. This method leveraged the coffee ring effect, a phenomenon where particles in a droplet of liquid concentrate at the edge as the liquid evaporates, enhancing detection sensitivity (1).

The researchers achieved the following results: the limit of detection (LOD) for 203 nm PP particles reached 31.25 micrograms per milliliter (μg/mL) (1). For larger PP particles, ranging from 382 to 2101 nm, the LOD was even lower, approximately 3.9 μg/mL (1). What the results demonstrated was that the high sensitivity reached indicated that it could be used to detect PP particles in various environments (1).

To test the practicality of their method, the researchers introduced 203 nm PP nanospheres into real food media, such as tea beverages and tea leaves (1). The minimum LOD for these tests was consistent with the laboratory results, at approximately 31.25 μg/mL (1).

The study highlighted the numerous advantages of this new detection method. Compared to current analytical techniques, it offers higher sensitivity, reproducibility, simplicity, and convenience (1). These attributes are crucial for advancing the study of microplastics, particularly in understanding their presence and effects in food and the environment (1).

With growing public and regulatory concern about microplastics, the research team proposed a new, workable solution for monitoring and managing PP contamination in food products. The study also provided a foundation for future studies to explore the health implications of microplastic ingestion and to develop strategies for mitigating their impact, improving human health and environmental sustainability.

References

(1) Xiang, T.; Sun, Y.; Ding, D.; et al. Microscopic Raman-based Rapid Detection of Submicron/Nano Polypropylene Plastics in Tea and Tea Beverages. Food Chem. 2024, 454, 139657. DOI: 10.1016/j.foodchem.2024.139657

(2) Ziani, K.; Ionita-Mindrican, C.-B.; Mititelu, M.; et al. Microplastics: A Real Global Threat for Environment and Food Safety: A State-of-the-Art Review. Nutrients 2023, 15 (3), 617. DOI: 10.3390/nu15030617