Photothermal Infrared Imaging of Nanoplastics in Human Cells with Nanoscale Resolution

The detection and intracellular tracking of nanoplastics in human cells remain critical challenges in understanding their biological impact. Here, we demonstrate the use of multimodal vibrational spectroscopy to identify and localize fluorescently labeled polystyrene nanoparticles (PS-NPs) within individual fibroblast and LN-229 glioblastoma cells. While fluorescence microscopy and Raman imaging confirmed the presence of PS-NPs around the nucleus, conventional Fourier-transform infrared (FT-IR) spectroscopy lacked the spatial resolution to detect intracellular nanoplastics. To overcome this limitation, we applied two advanced IR photothermal-based techniques: atomic force microscopy-infrared (AFM-IR) and optical photothermal infrared (O-PTIR) spectroscopy. AFM-IR enabled nanoscale chemical imaging and topographical mapping, while O-PTIR allowed label-free, noncontact detection of PS-NPs with submicron resolution. Both methods successfully identified characteristic spectral signatures of PS-NPs and revealed their perinuclear localization. Comparative analyses highlight O-PTIR's operational simplicity and spectral fidelity, and AFM-IR's superior spatial resolution. Our findings establish AFM-IR and O-PTIR as powerful, complementary tools for visualizing nanoplastics within single cells and lay the foundation for future studies exploring nanoplastic biodistribution and toxicity using vibrational spectroscopy.