A simple and reliable method for the qualitative and quantitative analysis of nano- and microplastics in organs for controlled preclinical studies

Toxicity studies of microplastics increasingly emphasize the importance of particle retention, transformation, and physicochemical properties within biological systems, as these factors critically influence hazard identification and dose–response interpretation. However, quantitative and qualitative analyses of microplastics in biological matrices remain technically challenging, and many existing digestion-based methods can alter particle properties, thereby confounding toxicological outcomes. Herein, we propose a novel methodology to provide quick, easy, non-destructive, cost-efficient, and reliable outcomes by offering a particle collection method for microplastics as-present in organs using proteinase K (PK) digestion and a simple quantification method based on ultraviolet-visible (UV-Vis) spectrophotometry. The test microplastic samples comprised three spherical polystyrene (0.1, 1, and 100 μm), two fragmented polystyrene (1 and 100 μm), one spherical polyethylene (10 μm), one fragmented polyethylene (100 μm), and two fragmented polypropylene (1 and 100 μm). Particles as-present in organs were successfully collected by conducting PK tissue digestion at 5 µg PK per mg dried tissue. The collected particles were then quantified using a standard curve, with absorbance measured at 750 nm. Spiking experiments with microplastics in mouse lung and mussel tissues showed > 90% accuracy and recovery for all test particles. Because the PK-based particle collection method is non-destructive, the collected particles can be further used to evaluate their physicochemical properties, such as size, shape, composition, and oxidative potential. However, the plastics treated with both acids and alkalis exhibited significant morphological, optical, and chemical changes, indicating that these methods are destructive to particles. Therefore, this simple, non-destructive approach enables quantitative and qualitative analyses for laboratory toxicological studies and qualitative identification of microplastics in unknown biological samples, providing a valuable tool for future toxicity and environmental research.