Covalently labeled fluorescence-MRI dual-modal polystyrene microspheres for imaging and analysis of microplastics in biological systems

Abstract

The widespread accumulation of microplastics (MPs) in the environment and their transfer along food chains pose growing threats to organism health, but MPs’ in vivo behaviours remain poorly understood due to the lack of stable and sensitive imaging tools. Herein, we report a robust covalent-labelling strategy for constructing dual-modal polystyrene microspheres (Fl-MRIPSs) for fluorescent and magnetic imaging in biological samples. Two polymerizable functional monomers—a rhodamine dye (RhSt) for fluorescence imaging and a gadolinium complex (DOTASt) for T₁-weighted MRI—were rationally designed and chemically incorporated into the polystyrene matrix via emulsion copolymerization. The resulting Fl-MRIPSs exhibit precise size control, uniform morphology, excellent monodispersity, and high colloidal stability. The covalent anchoring minimizes dye and Gd leakage while maintaining high fluorescence quantum yield, remarkable photostability, and strong MRI relaxivity. The Fl-MRIPSs show efficient cellular internalization with negligible cytotoxicity, enable high-contrast fluorescence visualization in zebrafish and mice, and provide significantly enhanced T₁-weighted MRI contrast in mouse subcutaneous tissue. This work establishes a generalizable, chemically stable dual-modal labelling platform for MPs, offering a powerful tool for elucidating their transport, biodistribution, and potential health risks in living organisms.