Advanced Raman Techniques for Micro- and Nanoplastics Detection

Four advanced Raman-based techniques, including surface-enhanced Raman scattering (SERS), Raman tweezers (RTs), tip-enhanced Raman scattering (TERS), and Raman mapping/imaging (RM/RI), have demonstrated great potential in detecting microplastics, according to a recent review in TrAC Trends in Analytical Chemistry (1).

Microplastics pose a significant danger to living organisms, impacting both aquatic and terrestrial ecosystems (2). These tiny plastic particles, often less than 5 mm in size, can be ingested by a wide range of organisms, from plankton to fish and birds. Once ingested, microplastics can cause physical harm, such as blockages and abrasions in digestive tracts, and may lead to malnutrition or starvation by creating a false sense of satiety (3). Moreover, microplastics can act as carriers for toxic substances, including heavy metals and persistent organic pollutants, which can leach into the tissues of organisms, leading to bioaccumulation and biomagnification through the food chain (3). Raman spectroscopy, despite its limitations, is a technique that could detect microplastics in oceanic environments, helping to preserve aquatic ecosystems (2).

Micro plastics mixed in the sand of the beach | Image Credit: © GaiBru Photo - stock.adobe.com

This review article, written by lead authors Jie Han from Xi'an Jiaotong University and Tejraj Aminabhavi from KLE Technological University and Korea University provides an overview of how SERS, RTs, TERS, and RM/RI are detecting micro- and nanoplastics in the environment, discussing the strengths and drawbacks of each technique. Traditional Raman spectroscopy, while widely used, has limitations in accurately analyzing these tiny plastic particles, especially those at the submicron and nanoscale (1).

The review is broken up with a section dedicated to each technique. The first technique covered in the review is SERS. The authors wrote that SERS technology enhances the Raman scattering signal, allowing for the detection of individual nanoplastics with diameters as small as tens of nanometers (1). SERS is especially useful for analyzing nanoplastics in aqueous environments. However, the diffraction limit restricts its effectiveness to particles larger than 100 nm (1).

For RTs, the technique manipulates and analyzes single particles. However, like SERS, it is limited by diffraction issues (1). For TERS, what makes this technique useful is that it can produce extremely high spatial resolution. This is important in nanoplastic detection because it means TERS can analyze nanoscale or even single-molecule imaging (1). Although it has been successful in analyzing microplastic particles, its application to nanoplastic detection remains limited to nanocomposite thin films, indicating that the current capabilities of this technology require more innovation (1).

And finally, the authors discuss RM/RI. These techniques surpass the diffraction limit by combining image analysis with advanced algorithms. As a result, this technique allows the detection of plastic particles as small as several tens of nanometers (1). Because this method has fewer limitations than the other abovementioned techniques, RM/RI is vital for single-particle analysis, which means it has high-throughput analysis and large-scale imaging of micro- and nanoplastics (1).

Despite the promising advancements, each of these Raman techniques faces significant challenges. Fluorescent interference, sample pretreatment, and inherent technical limitations are common issues that need to be addressed. As a result, the authors suggested that standardization of these advanced techniques should be the next step (1). By addressing the existing challenges and fostering interdisciplinary collaboration, the scientific community can accelerate technological advancements in micro- and nanoplastics research, which will enhance environmental monitoring and risk assessment, contributing to global efforts in mitigating plastic pollution.

References

(1) Dai, H.; Li, H.; Qiu, W.; et al. Nondestructive Analysis of Plastic Debris from Micro to Nano Sizes: A State-of-the-Art Review on Raman Spectroscopy-based Techniques. TrAC Trends Anal. Chem. 2024, 176, 117750. DOI: 10.1016/j.trac.2024.117750

(2) Araujo, C. F.; Nolasco, M. M.; Ribeiro, A. M. P.; et al. Identification of Microplastics Using Raman Spectroscopy: Latest Developments and Future Prospects. Water Res. 2018, 142, 426–440. DOI: 10.1016/j.watres.2018.05.060

(3) Lee, Y.; Cho, J.; Sohn, J.; Kim, C. Health Effects of Microplastic Exposures: Current Issues and Perspectives in South Korea. Yonsei Med. J. 2023, 64 (5), 301–308. DOI: 10.3349/ymj.2023.0048