Microplastics — plastic particles smaller than five millimeters — are pervasive in the environment. They can be ingested or inhaled into the human body, potentially affecting the person’s health. Despite this concern, research into the possible effects of microplastic pollution on human health has progressed slowly. Existing technology lacks the capability to both detect and localize tiny microplastic particles in the body without destroying the tissue. It is particularly difficult to detect and localize microplastic particles with formalin-fixed paraffin-embedded tissue (FFPE), which is commonly used for histopathological analysis and reporting. Scientists from the Medical University of Vienna partnered with other institutions to develop a way to precisely locate microplastics in tissue without causing any damage. The researchers used optical photothermal infrared (OPTIR) spectroscopy, also known as mid-infrared photothermal (MIP) microscopy, to perform label-free, nondestructive analyses of micro- and nanoplastics in mammalian tissue samples. OPTIR provides high-quality, artifact-free spectral images in a contactless manner. It outperforms traditional IR spectroscopy in spatial resolution and signal to noise ratio, achieving spatial resolution beyond the limits of conventional Fourier-transform infrared (FTIR) spectroscopy. OPTIR works by capturing the reaction of different materials to IR laser light. The IR light heats the samples locally, causing plastics like polyethylene (PE), polystyrene (PS), and polyethylene terephthalate (PET) to exhibit behaviors characteristic of their chemical structures. These behaviors produce specific signals that are detected by a second light source, creating a unique IR fingerprint that allows chemical identification. OPTIR preserves tissue structure, so subsequent histopathological analyses can be performed on the tissue to assess the impact of microplastic accumulation in the body. The researchers analyzed FFPE samples using OPTIR spectroscopy and precisely located PE, PS, and PET particles in the tissue. During analysis the tissue structure remained intact, enabling the researchers to directly combine chemical analysis with subsequent histological or genetic assessments. Not only were the researchers able to detect the microplastic particles, but they were also able to examine the microplastics in connection with tissue changes. Hematoxylin and eosin (H&E) analysis revealed a spatial association between inflammation in the tissue and the presence of microplastics. “In the recently published study, we were able to identify various microplastic particles in human colon tissue, including PE, PS, and PET,” Lukas Kenner, who led the research, said. “These were found to be conspicuously frequent in areas with inflammatory changes.” In further experiments with mice and 3D cell cultures, the team reliably detected extremely small particles, with diameters of only 250 nm, using OPTIR. The researchers used a semiautomated image analysis method that incorporated machine learning algorithms to accelerate the detection process. This method improved throughput and minimized the potential for human error. By introducing an optimized workflow that protected the tissue architecture, the OPTIR method allowed the team to identify and characterize microplastic particles in FFPE samples while obtaining the information required to interpret the role of the particles in a clinical context. The use of OPTIR could enhance understanding of microplastic accumulation in routine organ tissue slides and the implications for human health, including the possible link between microplastic exposure and chronic disease. The morphological H&E features, observed in proximity to the identified microplastics, could indicate a link between microplastic exposure and colon inflammation. Microplastics are present in marine ecosystems, freshwater bodies, soil, and the air. PE, PS, and PET plastics are found in numerous objects, from cling film and plastic bags to drinking bottles and food packaging, that are used daily. To date, the only analytical methods available to investigate the impact of microplastics either could not be used without destroying the tissue, or could not be used to identify the precise location of the microplastic particles. “The application of OPTIR technology that we have established shows, for the first time, that both are possible: precise chemical identification, and preservation of spatial tissue information — a milestone for medical microplastics research,” Kenner said. The research was published in Analytical Chemistry (www.doi.org/10.1021/acs.analchem.4c05400) and Scientific Reports (www.doi.org/10.1101/2025.01.09.24319030).