Tracking Microplastics Inside Living Organisms Requires a Fundamentally Different Approach to Imaging

Microplastics have been detected in ocean sediments, Arctic ice, agricultural soils, and human tissues including blood, liver, and brain samples. Global plastic production now exceeds 460 million tons annually, and millions of tons of microplastics and nanoplastics enter the environment each year. The scientific community has documented where these particles end up. What remains poorly understood is what happens to them once they get there.

Inside a living organism, a microplastic particle does not simply sit still. It moves through tissues, accumulates in organs, interacts with biological molecules, undergoes physical and chemical transformation, and eventually breaks down - or does not. Understanding those processes requires watching them happen. Current methods make that nearly impossible.

The Limits of Current Detection

The techniques that environmental scientists currently use to detect microplastics in biological samples - infrared spectroscopy, mass spectrometry, electron microscopy - share a fundamental limitation. They are destructive. You cannot measure a particle's location and then continue observing the living system it came from. Each measurement requires sacrificing the sample.

The result is a series of snapshots rather than a continuous story. Researchers can measure particle concentrations in tissues at specific time points, but cannot directly observe the transport routes particles take, how they transform chemically or physically over time, or which breakdown products are produced and where they go.

"Most current methods give us only a snapshot in time," said corresponding author Wenhong Fan. "We can measure how many particles are present in a tissue, but we cannot directly observe how they travel, accumulate, transform, or break down inside living organisms."

A Different Approach to Labeling

Fluorescence imaging is already used in biological research to track molecules and cellular structures in living systems. The challenge for microplastics is that attaching fluorescent dye molecules to the surface of a plastic particle creates an unstable label. Dyes can leach away from the surface, produce false signals when they aggregate independently of the particle, or quench - lose their fluorescent signal - in the complex chemical environment of a biological tissue.

The proposed strategy published in New Contaminants by Zhang, Ren, Liu, and colleagues addresses these problems through a different labeling architecture. Rather than attaching fluorescent dyes to the surface after the fact, the method incorporates fluorescent monomers into the polymer chain during synthesis - building the light-emitting property directly into the material's molecular structure.

The fluorescent monomers used belong to a class called aggregation-induced emission materials. These molecules emit stronger fluorescent signals when they are packed together - the opposite behavior from conventional fluorescent dyes, which tend to self-quench when concentrated. This property is advantageous for microplastic tracking: the plastic matrix aggregates the fluorescent groups naturally, producing a stable, bright signal rather than a diminished one.

What This Enables

Because fluorescent groups are distributed uniformly throughout the polymer structure rather than concentrated on the surface, the labeling persists through fragmentation. When a microplastic particle breaks down into smaller pieces - nanoplastics, which are even harder to detect than their parent particles - each fragment retains fluorescence. This makes it possible to track the complete degradation pathway, not just the original particle.

The approach also allows tuning of multiple parameters during synthesis: brightness, emission wavelength, particle size, and shape can all be varied systematically. Using particles with different emission wavelengths, researchers could potentially track multiple particle populations simultaneously or distinguish between intact particles and specific degradation products.

What Has and Has Not Been Established

The paper proposes and describes the strategy; it does not present the results of live animal tracking experiments. The authors acknowledge that experimental validation of the approach in complex biological systems - where immune responses, metabolic processes, and tissue chemistry all interact with the labeled particles - is still required. Whether the aggregation-induced emission approach maintains its advantages under the specific conditions found in different tissues, and whether the labeled particles behave identically to unlabeled ones in biological systems, are questions that require direct experimental testing.

"Clarifying the transport and transformation processes of microplastics inside organisms is essential for assessing their true ecological and health risks," Fan said. "Dynamic tracking will help us move beyond simple exposure measurements toward a deeper understanding of toxicity mechanisms."

The research was published in New Contaminants, doi: 10.48130/newcontam-0026-0003.