Fluorescently labelled polypropylene as a model microplastic for cellular imaging

Polypropylene (PP) is the second most produced plastic globally and is environmentally pervasive in the form of microplastics (MPs). The cellular localisation and fate of MPs within biological systems remain poorly understood. We present a method for the covalent functionalisation of PP with the fluorescent label rhodamine B (Rb) and its subsequent MP evaluation in a human embryonic kidney model cell line (HEK293T). Rb was successfully coupled into PP (PPRb) under Steglich esterification conditions. PPRb is stable under physiological pH and so can be utilised in vitro, offering a significantly improved MP model for conventional staining methods that can definitively locate MPs in human cells. Cellular uptake of PPRb was rapid (≤1 h), and PPRb was non-toxic up to 70 µM and was not observed to localise within the nucleus. Increased mean lysosomal fluorescence intensity suggested an endosomal uptake mechanism followed by significant clearance over a 48 h period. This approach provides a robust platform for definitive microplastic tracking, enabling reliable, standardised studies of polymer–cell interactions across biological systems.