Evaluating Micro- and Nanoplastics from Chewing Gum with SERS

Microplastics (MPs) and nanoplastics (NPs) often go unnoticed due to suboptimal analytical tools, making their way inside our bodies through various means, and, because of inferior analytical tools, often go unnoticed, resulting in their becoming an increasing health hazard. Although surface-enhanced Raman spectroscopy (SERS) is utilized in the finding of NPs, challenges arise at low concentrations due to their low Raman cross section, as well as their inability to situate within hotspots due to their size and shape. Cuong Cao from the Institute for Global Food Security at the School of Biological Sciences of Queen’s University in Belfast and his team of researchers conducted a preliminary exploratory study and detected the presence of MPs by automated Raman spectroscopy and subsequently NPs by using nanoparticle-on-film SERS (NPoF SERS) substrate released from chewing gum base plastic, a technique that has potential in screening a varied array of environmental pollutants, as well as a point-of-site tool when coupled with a handheld Raman instrument. Cao spoke to Spectroscopy about this work, and the resulting paper.

Your paper (1) presents a unique and cost-effective method using household aluminum foil and copper slug tape to create nanoparticle-on-film (NPoF) substrates for surface-enhanced Raman spectroscopy (SERS). What motivated this research in the first place?

This study was motivated by the need for affordable, accessible, and effective tools to address the growing environmental and health challenges posed by microplastics (MPs) and nanoplastics (NPs). Detecting both MPs and NPs is particularly difficult because existing methods often specialize in one or the other, and current techniques, such as vibrational spectroscopy and mass spectrometry, have limitations in terms of cost, complexity, or sensitivity for low concentrations and nanoscale plastic particles. We attempted to bridge this gap by combining automated Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS) with advanced filtration techniques, enabling the simultaneous detection of MPs and NPs in complex real-world samples. This cost-effective solution provides a foundation for developing universal methods to monitor plastic pollution and its impacts more effectively.

In addition, a preliminary study to know whether the plastic base containing chewing gums releases microplastics and nanoplastics (MNPs) in the oral cavity while chewing or not was performed. Again, what motivated the specificity of this study?

Concerns about chewing gum as litter have been raised by government agencies and media outlets since the early 2000s (2,3). In 2023, the UK allocated over £1 million to clean up chewing gum from streets (4). When discussed with my PhD student, Udit Pant, this led us to ask: “If chewing gum in the environment can contribute to pollution and release smaller plastic particles, could the same occur when we chew it?” Chewing gum, estimated at 574 billion pieces consumed annually worldwide (5), often contains non-biodegradable plastic bases. Yet, most people don’t realize this. For example, an Iceland-commissioned study found that 85% of 2,000 people surveyed didn’t know gum contains plastic (6). When we sought evidence-based studies on whether chewing gum releases plastic particles during chewing, we found none. This gap in research motivated us to explore potential plastic exposure from everyday products, using chewing gum as a case study to investigate the release of MPs and NPs.

What are the long-range ramifications of the presence of MNPs in the gum, or any food for that matter?

The long-term implications of the presence of MPs and NPs in chewing gum or food largely stem from their potential to serve as an overlooked source of plastic exposure during consumption. Our preliminary study demonstrated that chewing gum can release MPs and NPs into the oral cavity. Therefore, there is a possibility of ingestion of these particles through daily habits.

While we did not investigate the toxicity of MNPs within the context of this study, our preliminary findings aim to enhance scientific understanding of how everyday products may contribute to plastic exposure and does not imply intentional harm or negligence. This knowledge helps guide further research into exposure routes and potential health implications. In a broader context, it is necessary to establish transparency about the materials used in consumables and to encourage innovation aimed at reducing plastic content in products.

Would the presence be more of a potential threat in food that you swallow and digest rather than just chew, like gum?

While chewing gum is not meant to be swallowed and digested, the act of chewing does release MPs and NPs into the saliva, which is inevitably swallowed. This means that even though the gum base itself is not ingested, MNPs released during chewing can still unavoidably enter the digestive system. This suggests that everyday habits, such as chewing gum, may contribute to overall plastic exposure, warranting further investigation.

You mention in your paper that mass spectrometry (MS) and Fourier transform infrared (FT-IR) spectroscopy are currently used to detect MNPs, in addition to Raman. What are the benefits and drawbacks of these techniques?

MS, FT-IR, and Raman spectroscopy are commonly used techniques for detecting MPs and NPs. Each has its own advantages and limitations. For instance, MS is highly sensitive and provides detailed chemical information but is expensive, requires sample destruction, and cannot provide information about particle morphologies. FT-IR and Raman spectroscopy are non-destructive and user-friendly but struggle to detect very small particles like NPs. For more details on the strengths and weaknesses of these techniques, I recommend referring to reviews, including our publication in Comprehensive Analytical Chemistry (7).

Briefly summarize your findings, and the conclusions you came to after reviewing these findings.

Our study presents a method for detecting both MPs and NPs by combining automated Raman spectroscopy with a sensitive, low-cost SERS-based approach using household materials as SERS substrates. We demonstrated its effectiveness by detecting NPs at low concentrations and confirmed that chewing gum releases MPs and NPs into saliva, highlighting gum as an unrecognized source of plastic exposure. Our findings fill gaps in MNP detection and underscore the importance of raising awareness about plastic contamination in everyday products.

What advantages do the portability of your method provide?

The portability of our method, made possible by cost-effective and flexible nanoparticle-on-film (NPoF) substrates, provides key advantages. It enables the possibility of on-site detection of MPs and NPs using handheld Raman spectrometers, removing the need for lab-based analysis. This is especially beneficial for environmental monitoring, food safety checks, and industrial quality control. The use of household materials also ensures accessibility, even in resource-limited settings.

What difficulties did you encounter in your work, specifically sampling and analytical challenges?

One of the main challenges we faced was the complexity of the saliva samples in the chewing gum study. Saliva contains a mix of water-soluble and insoluble components, along with organic and biogenic matter, making it difficult to isolate MPs and NPs without losing the analytes. The sample preparation process involved multiple filtration and centrifugation steps, requiring meticulous handling to prevent contamination or particle loss. Avoiding external contamination from environmental MNPs was another hurdle, which we addressed by implementing strict cleaning procedures and working in controlled environments. Additionally, analyzing low-concentration samples of MNPs was a demanding task that required careful optimization and examination.

How can your results be applied?

Our results could be applied to environmental monitoring for detecting MPs and NPs in water, air, and soil, as well as in food safety for identifying plastic contamination in consumables and packaging. The cost-effective and portable nature of the method makes it suitable for on-site and real-time analysis, enabling its use in both industrial and resource-limited settings.

What are the broader implications?

This study contributes to addressing MNPs pollution, which is a global concern, by introducing an effective and accessible method to detect MPs and NPs while uncovering overlooked sources of exposure, such as chewing gum. It suggests the need to explore sustainable alternatives for food products and highlights the importance of increasing awareness about everyday items as potential contributors to MNP exposure. These findings would suggest further research on environmental health and public safety, emphasizing the need for continued investigation into penetration routes and potential health impacts of MNPs.

Were there any factors that might affect the accuracy of your findings?

Yes, factors such as sample complexity, potential contamination from external MNPs, and the challenges of detecting very low concentrations of MNPs, particularly NPs, could affect accuracy.

How do you imagine the results of your study can/will be applied?

I envision that this method could be used for monitoring MNPs in environmental and industrial settings, food safety assessments, and public health research. It could also support policymakers and industries in addressing plastic contamination and promoting sustainability initiatives.

Are there any next steps in this research?

The next steps involve refining the method to achieve greater sensitivity and reproducibility, expanding its application to more complex matrices, and exploring its use in larger-scale studies to quantify MNP exposure and assess potential health impacts. Collaboration with industries and policymakers to implement the method in practical settings would also be a key focus.

References

1. Pant, U.; Tate, J.; Liu, X.; Birse, N.; Elliott, C.; Cao C. From Automated Raman to Cost-Effective Nanoparticle-on-Film (NPoF) SERS Spectroscopy: A Combined Approach for Assessing Micro- and Nanoplastics Released into the Oral Cavity from Chewing Gum. J. Hazard. Mater. 2025, 486, 136978. DOI: 10.1016/j.jhazmat.2024.136978

2. Chewing Gum Litter. Parliamentary Office of Science and Technology website. 2003, 201. https://www.parliament.uk/globalassets/documents/post/pn201.pdf (accessed 2024-01-08).

3. Asher, C. Why Your Chewing Gum Can Be Secretly Destroying the Planet. BBC Science Focus 2023.https://www.sciencefocus.com/science/why-your-chewing-gum-could-be-secretly-destroying-the-planet (accessed 2024-01-08).

4. More than £1.2m Funding for Councils to Clean Up Chewing Gum from our Streets. Gov.UK website 2023.https://www.gov.uk/government/news/more-than-12m-funding-for-councils-to-clean-up-chewing-gum-from-our-streets (accessed 2024-01-08).

5. Pointing, C. 574 Billion Pieces of Gum Chewed Every Year Contain Plastic. Plant Based News 2022.

6. Lindsay, J.Did You Know Most Chewing Gum Contains Plastic? Metro 2018. https://metro.co.uk/2018/08/02/know-chewing-gum-contains-plastic-7790722/ (accessed 2024-01-08).

7. Bibi, A.; Can, A.; Pant, U.; Hardiman, G.; Hill, D.; Elliott, C.; Cao, C. Chapter Six - A Review on State-of-the-Art Detection Techniques for Micro- and Nano-Plastics with Prospective Use in Point-of-Site Detection. Comprehensive Analytical Chemistry; J. L. D. Nelis, A. S. Tsagkaris, Eds. Elsevier, 2023, 143–196. DOI: 10.1016/bs.coac.2022.11.003

Cuong Cao is a Reader and Director of the Biochemistry Program at the Institute for Global Food Security, School of Biological Sciences, Queen’s University in Belfast, UK. He holds a PhD from Sungkyunkwan University, South Korea, and subsequently conducted postdoctoral research at the Technical University of Denmark and Nanyang Technological University of Singapore. Appointed as a lecturer at Queen’s University Belfast in 2013, Dr. Cao established the Applied Micro- and Nanotechnology Research Group. His research addresses global challenges in infectious diseases, antimicrobial resistance, food integrity, and environmental pollution by leveraging micro- and nanotechnology innovations. This includes the synthesis of plasmonic and catalytic nanomaterials, the development of nanoplasmonics-based biosensing platforms, and the development of cost-effective, portable detection methods aimed at enhancing healthcare affordability and accessibility.