Noncovalent radiolabeling of microplastics using a desferrioxamine-conjugated Nile Red derivative for quantitative in vivo tracking

BACKGROUND: Microplastics are now recognized as environmental contaminants with growing concerns regarding their potential impact on ecosystems and human health. Understanding their in vivo fate is essential for accurate risk assessment; however, quantitative tracking of microplastics in living systems remains challenging. Existing labeling approaches often rely on surface modification or covalent functionalization, which can alter the intrinsic physicochemical properties of the particles and compromise biological relevance. To date, no established analytical methodology enables non-destructive, quantitative, and in vivo tracking of microplastics while preserving their native characteristics. RESULTS: Here, we report a noncovalent radiolabeling method using a desferrioxamine (DFO)-conjugated Nile Red derivative (DFO-Hexyl NR) that enables dual fluorescence imaging and radiometal chelation without surface modification of microplastics. The dihexylamino substituent enhances hydrophobic interactions with pristine polymer surfaces, while the incorporated DFO moiety allows stable Zr chelation. This approach preserved the intrinsic physicochemical characteristics of PTFE, PS, and PET microplastics, as confirmed by FT-IR spectra, zeta-potential and contact angle measurements, and showed robust stability under acidic, alkaline, saline, and serum conditions. Using this strategy, Zr-labeled PTFE microplastics were applied to in vivo positron emission tomography following oral administration and revealed predominant gastrointestinal retention with minimal systemic absorption over 48 h. Additional radiolabeling experiments with multiple plastic types demonstrated the broad applicability of this method to polymers with distinct chemical structures. SIGNIFICANCE: The described radiolabeling platform enables non-destructive and quantitative in vivo tracking of environmentally relevant microplastics and preserves their intrinsic physicochemical properties. This approach overcomes the limitations of conventional surface-modification-based labeling strategies and provides a fundamentally new analytical capability for the study of microplastic behavior in living systems. The methodology establishes a robust analytical foundation for the investigation of polymer-specific biokinetics, chronic exposure scenarios, and comparative assessments across exposure routes.