Researchers have used optical photothermal infrared (O-PTIR) spectroscopy to chemically identify microplastics inside intestinal epithelial cells in vitro while assessing their cellular effects. The research addresses two long-standing challenges in microplastics research: verifying intracellular plastic particles without labels or dyes, and linking their presence directly to biological response.
The team from Australia exposed a rat-derived intestinal epithelial cell line (IEC-6) to mechanically degraded, environmentally relevant microplastics generated from common household polymers, including polyethylene terephthalate (PET), polystyrene (PS), polyvinyl chloride (PVC), and polytetrafluoroethylene (PTFE). Unlike studies based on uniform polymer microspheres, the particles used were irregular in shape and composition, better reflecting real-world microplastic exposure.
The team combined confocal fluorescence microscopy with O-PTIR spectroscopy to verify uptake and composition. O-PTIR provided sub-micron spatial resolution and polymer-specific infrared fingerprints, allowing individual microplastic particles to be chemically distinguished within intact cell monolayers. Microplastics as small as ~1 µm were identified based on characteristic vibrational bands, even when embedded in cytoplasm and surrounded by strong biological signals.
Notably, O-PTIR was also used to probe biochemical changes in the same cells. Hyperspectral O-PTIR datasets were analyzed using chemometric methods to isolate cytoplasmic spectra free of polymer contributions. Principal component analysis revealed clear separation between control and microplastic-exposed cells, driven by changes in protein and lipid-associated infrared bands.
Cells exposed to mixed and single-polymer microplastics showed spectral features consistent with oxidative stress, lipid peroxidation, and disruption of protein secondary structure. In particular, shifts in amide I and II bands suggested alterations in protein folding and early aggregation, while changes in carbonyl-associated bands pointed to oxidative damage of lipid species.
The authors emphasize that the strength of the approach lies in its integration: O-PTIR simultaneously confirmed microplastic presence, determined polymer identity, and captured localized biochemical effects without destroying the sample. They note that extending this approach beyond in-vitro models will be an important next step for evaluating microplastic interactions in biological systems.
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