Recently, Professor Luo Tengfei from the University of Notre Dame in the United States and his collaborators have, for the first time, revealed the morphology of nanoplastics in natural seawater.

In the study, they used a unique bubble deposition technique (SSBD, shrinking surface bubble deposition) to capture and observe trace amounts of nanoplastics in seawater.

During the period, the research team tested seawater samples from Shenzhen, China, California, Texas in the United States, Ulsan in South Korea, and the Gulf of Mexico.

The team found that nanoplastics are ubiquitous in seawater worldwide, with various shapes and chemical compositions. What is more surprising is that they found nanoplastic particles derived from the material of mineral water bottles in seawater 300 meters deep in the Gulf of Mexico.

Since the bubble deposition can concentrate these nanoparticles on a base surface, the research team used a scanning electron microscope to intuitively display the morphology and size of various types of nanoplastics in nature, including polystyrene, nylon, and polyethylene terephthalate for the first time.This study not only addresses the current issues of detecting and visualizing nano-plastics in the natural world but also provides new insights for environmental and toxicological research.

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Overall, this research has demonstrated the ubiquity of nano-plastics in the ocean and, for the first time, visualized them through scanning electron microscopy and transmission electron microscopy, revealing the true form of nano-plastics in nature, providing key information for the toxicological study of nano-plastics and the study of marine ecology.

Regarding the relevant papers, the reviewers have indicated that a combination of various analytical techniques can lead to a more thorough analysis of nano-plastics.

For instance, when observing polystyrene, although it is abundant in the ocean, it is prone to decompose into smaller styrene oligomers. These oligomers are too small to be captured by scanning electron microscopy techniques, but Raman spectroscopy can detect polystyrene.

It is reported that the SSBD (Surface-Enhanced Scattering Based Detection) technique can directly mix the sample to be tested with a suspension of nano-metal particles. In the study, the research team used 10nm silver particles, which, under the excitation of pulsed laser, produce a plasmonic effect that generates bubbles.The temperature field change caused by the plasma effect leads to the formation of a "Marangoni flow" around the bubble — this is a mass transfer phenomenon caused by the gradient of surface tension.

The formed "Marangoni flow" transports suspended particles in the liquid to the surface of the bubble, where they are "captured" by the bubble and ultimately accumulated at the three-phase contact line.

When the laser excitation is stopped, the bubble gradually shrinks and eventually disappears, and the captured particles are finally deposited on the substrate for subsequent detection and analysis using techniques such as Raman spectroscopy and scanning electron microscopy.

Compared to other detection methods that require cumbersome filtration of the sample, SSBD can detect target samples at ultra-low concentrations without complex pre-treatment operations.

In addition, a paper published by the team in Advanced Materials Interfaces in 2020 shows that the SSBD technology can alleviate the problem of biomolecule degradation in traditional photothermal deposition technology, that is, it can improve the detection limit without damaging the biological function.Based on these two points, the research team believes that this research outcome has great potential in the detection of trace solid pollutants at ultra-low concentrations and in biosensing.

For example, using SSBD to concentrate biomarkers in blood samples, thereby improving sensitivity and enhancing the early detection of cancer cells, which can lead to earlier detection and treatment of cancer.

Millions of tons of plastic waste enter the oceans every year.

In fact, what exactly are the nanoplastic particles in the ocean? No one knew before.

As a primary material for daily production and life, the global production of plastic reaches as high as 400 million tons each year, and as much as millions of tons of plastic waste will enter the oceans.Over time, these plastics will break down into micro- or nano-scale particles invisible to the naked eye due to exposure to ultraviolet light and mechanical degradation by ocean turbulence.

With current technologies such as scanning electron microscopy and Raman spectroscopy, it is already possible to observe plastic particles at the micro-scale (1-5000 micrometers) in marine and freshwater environments.

However, when these plastic particles reach the nano-scale (<1 micrometer), existing technologies and methods are no longer able to detect nano-plastics in the natural environment.

Previous research has found that the toxicity of micro-plastics and nano-plastics to living organisms is negatively correlated with particle size and shape.

This means that smaller plastic particles are more likely to penetrate the protective membranes of living organisms and may carry unknown toxic substances or heavy metals that can infiltrate into biological and human systems.Therefore, understanding the forms in which nanoplastics exist in nature is particularly important for their toxicity and environmental research. Currently, the detection of nanoplastics is mainly based on pyrolysis coupled with gas chromatography-mass spectrometry.

However, this technology requires a large number of filtration and concentration steps, and nanoplastics will be volatilized in the high-temperature environment of pyrolysis coupling, which cannot provide effective information on size and form under natural environmental conditions.

Several friends have kindly provided experimental seawater.

In response to bubble generation, Luo Tengfei has previously accumulated some achievements. Based on this, he wants to have a deeper understanding of the heat and mass transfer laws at the microscale.Later, he and his team observed the highly concentrated sediments formed after the shrinkage of bubbles in experiments, which opened the door for the determination of this topic.

After communicating with Professor Xu Wei, a marine ecologist at Texas A&M University in the United States, Luo Tengfei decided to use this technology to "capture" and identify marine nano-plastic pollutants in seawater.

Previously, they had proven that this concentration technology would not cause the degradation of organic molecules due to high temperatures. It can capture samples under very low concentration conditions and retain the original structure of the samples to the greatest extent.

This just provides a theoretical basis for the visualization of marine nano-plastics in the natural world.

After basically determining the feasibility of the experiment, they began to collect seawater samples from around the world, and a total of 5 seawater samples were obtained from Shenzhen, China, California, USA, Texas, USA, Ulsan, South Korea, and the Gulf of Mexico.Afterward, they began to use SSBD technology to analyze these samples, successfully concentrating several types of nano-plastics that might exist in the ocean, and ultimately identified and visualized them through Raman spectroscopy and scanning electron microscopy.

Luo Tengfei said: "The success of the research is inseparable from Professor Xu of Texas A&M University, who is a good friend of playing football together during our doctoral studies.

A few years ago, Professor Xu saw the media report of my bubble experiment for the first time on the International Space Station and asked me if I had considered applying this technology to the detection of nano-plastics in the ocean."

Based on this idea, they formulated a detailed experimental plan and mobilized several friends to help collect water samples globally.

It is precisely with the help of friends from various sides that this series of research from space to the seabed, spanning more than 400 kilometers, was facilitated.Ultimately, the related paper was published under the title "Direct observation and identification of nanoplastics in ocean water" in Science Advances[1].

Seunghyun Moon is the first author, and Xu Wei and Luo Tengfei serve as co-corresponding authors.

Furthermore, although they have not yet utilized AI technology in this study, AI has played a crucial role in Luo Tengfei's other research.

It is understood that most of the team's topics are closely related to computer science, such as in their previous research on polymers, where they trained the largest existing polymer database based on a recurrent neural network, creating a benchmark database containing about one million polymers—PI1M, which provides good data information for polymer informatics research.

And indeed, PI1M has become a test database used by researchers in the field of polymer information research on multiple occasions since then.In addition to this, they also employ active learning strategies to explore polymers with high thermal conductivity. This research combining machine learning with molecular dynamics has greatly enhanced their screening capabilities for large-scale polymer databases and has discovered more polymers with excellent performance for the engineering field.

Similar machine learning strategies have also been applied to the optimization of thermoelectric materials. In a paper published in Advanced Materials in 2023, they proposed a hybrid data-driven strategy integrating Bayesian optimization and Gaussian process regression to optimize the composition of various elements in thermoelectric materials.

The involvement of artificial intelligence has accelerated the development and optimization of various material systems, while reducing the number of experiments, saving time and cost.

For this study, considering the detection sensitivity of SSBD under ultra-low concentration conditions, they are currently trying to apply this technology to bottled water of different brands, to statistically analyze the types of nano-plastics contained and to conduct visual research on their morphology. It is expected that AI technology will greatly enhance test throughput and sensitivity.

For comparison, they also hope to use pyrolysis coupled with gas chromatography-mass spectrometry to quantify the total plastic content in water samples.In order to understand the relationship between particle density and the concentration of nano-plastic particles in water, they plan to sample specific marine areas, beaches, and offshore areas, and apply SSBD technology to these samples, followed by statistical analysis of different types and forms of plastic particles.

At the same time, they also want to use machine learning methods to associate the cumulative flow with the experimentally measured sediment density, thereby establishing a nonlinear correlation, and thus determining the best experimental conditions for the detection limit of nano-plastics.