Tokyo University of Science Unveils Real-Time Tracking of Nano-Microplastics in Living Organisms
Researchers at Tokyo University of Science (TUS) have achieved a pioneering advancement in environmental health science by developing fluorescent nano-microplastics that enable real-time visualization of their movement inside the body. This breakthrough addresses a critical gap in understanding how these pervasive pollutants behave once ingested, potentially reshaping our knowledge of associated health risks.
Led by Associate Professor Masakazu Umezawa from the Department of Medical and Robotic Engineering Design, the team created irregularly shaped nano-microplastics (nMPs)—particles smaller than 1 micrometer—from common polymers like polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and polystyrene (PS). These were loaded with near-infrared second window (NIR-II) fluorescent dyes, such as IR-1061, allowing deep-tissue imaging without invasive procedures.
The Global Microplastics Crisis and Japan's Unique Position
Microplastics, defined as plastic fragments less than 5 millimeters in size, contaminate oceans, rivers, air, and food chains worldwide. Global plastic waste is projected to double from 188 million tons in 2016 to 380 million tons by 2040, with humans ingesting an estimated 100 to 300 particles daily through water, seafood, and salt. In Japan, despite an impressive 84% plastic recycling rate, rivers like the Edo River show seasonal spikes in microplastic levels, up 2.7 times from April to September, highlighting ongoing challenges from urban runoff and marine litter hotspots around Tokyo Bay.
Japan's seafood-heavy diet amplifies ingestion risks, with studies detecting microplastics in 60% of wild flathead grey mullets near coastal areas. This innovation from TUS positions Japanese universities at the forefront of tackling these issues through advanced nanotechnology.
Overcoming Limitations in Microplastics Detection
Traditional methods like Fourier transform infrared spectroscopy or Raman microscopy identify microplastics but require excised tissues, preventing dynamic observation in living subjects. Spherical polystyrene beads used in prior models fail to replicate real-world irregular, weathered fragments from environmental degradation.
NIR-II imaging, operating at wavelengths over 1000 nm, penetrates 1-2 cm into tissues with minimal scattering and autofluorescence—far superior to visible light or NIR-I. TUS researchers leveraged this for non-invasive, real-time tracking, a first for diverse polymer nMPs.
Step-by-Step Synthesis of Fluorescent Nano-Microplastics
The synthesis process begins with fragmenting plastic granules in solvents like tetrahydrofuran (THF) for PE and PP, or acetonitrile for PET, creating nanosized dispersions. These are mixed with IR-1061 dye under nitrogen at 55°C, allowing thermal expansion for dye infiltration. Bovine serum albumin (BSA) is added dropwise to stabilize irregular shapes and ensure water dispersibility, evaporating organics over 48 hours. Particles retain over 80% fluorescence for 30 days.
- Polymer fragmentation: 14 days stirring in THF yields 30-300 nm particles.
- Dye loading: 55°C heating incorporates 3-24 µg IR-1061 per 6 mg plastic.
- Stabilization: BSA prevents aggregation, mimicking protein coronas in vivo.
For visible studies, Nile red dye enables cellular uptake visualization.
In Vitro and In Vivo Experiments: Design and Execution
In vitro, Nile red-loaded nMPs (2 µg/mL) were incubated with mouse fibroblasts (3T3-L1 cells) for 30 minutes. Fluorescence microscopy revealed cytoplasmic uptake via endocytosis, clustering near nuclei—efficient at concentrations lower than spherical models.
In vivo, 1.2 mg nMPs (6 mg/mL, 0.2 mL) were orally administered to 8-week-old female BALB/c nu/nu mice. NIR-II imaging (980 nm excitation, SAI-1000 system) tracked from 30 minutes to 48 hours, with feces analyzed for excretion. Protocols followed TUS animal care guidelines.
Photo by Ryunosuke Kikuno on Unsplash
Key Findings: Movement Patterns and Excretion Dynamics
nMPs accumulated in the stomach for up to 8 hours, migrated to intestines, and were fully excreted in feces by 48 hours—no detection in liver, lungs, or other organs, indicating negligible intestinal absorption. Smaller PP particles (<100 nm) showed prolonged intestinal retention compared to larger PE/PS (135-347 nm).
- Stomach retention: 0.5-8 hours across polymers.
- Intestinal transit: Size-dependent; PP slowest excretion.
- Zero translocation: GI barrier prevents systemic entry in acute exposure.
These patterns differ from spherical models, underscoring shape and composition's role.
Implications for Human Health and Risk Assessment
While acute exposure shows fecal excretion, chronic ingestion—estimated at 258-312 particles daily—may lead to cumulative retention, inflammation, or oxidative stress. Recent 2026 studies link microplastics to 90% of prostate tumors and gene expression changes, though ubiquity claims face scrutiny. TUS's platform enables long-term studies on organ accumulation, inhalation routes, and interactions with gut microbiota.
Read the full study in Environmental Science: Advances for detailed results.
Japan's Leadership in Microplastics Research at Universities
Japan excels in nanotechnology, with TUS's work complementing efforts like Subaru Telescope's citation impact and iPS cell therapies. Universities drive policy, from river monitoring to seafood safety. TUS's interdisciplinary approach—merging engineering, medicine, robotics—exemplifies Japan's innovation ecosystem.
For aspiring researchers, explore research jobs in environmental nanotech or university opportunities in Japan.
Future Directions: From Models to Policy and Mitigation
Next steps include chronic dosing, inhalation models, surface-modified nMPs, and human-relevant sizes. This could inform regulations on plastic additives and wastewater treatment. Assoc. Prof. Umezawa notes: "This method clarifies MPs' internal movement, supporting comprehensive risk assessments."
Globally, it aids reducing production and enhancing recycling—Japan's model for others.
Career Opportunities in Nanotech and Environmental Science
This breakthrough highlights demand for experts in NIR imaging, polymer synthesis, and toxicology. TUS and Japanese universities offer faculty positions, postdocs, and PhDs. Check career advice or review professors at institutions like TUS.
- Skills: Fluorescence microscopy, animal models, nanomaterials.
- Roles: Research assistant, lecturer in env engineering.
- Japan focus: JSPS grants fund such projects.
Visit postdoc jobs and university jobs for openings.
Photo by Beth Macdonald on Unsplash
Conclusion: A Step Toward Safer Environments
TUS's fluorescent nano-microplastics tracking illuminates a path to mitigating invisible threats. By revealing low absorption yet size-dependent retention, it guides safer policies and inspires global research. For professionals, it's a call to innovate in higher education's vital role. Explore higher ed jobs, rate your professor, and career advice to join this field.