Evaluating NIR-II-Emissive Graphene Quantum Dot Biodistribution, Toxicity, and Clearance for In Vivo Fluorescence Imaging

Near-infrared-II (NIR-II) fluorescence has emerged as a promising modality for biomedical imaging due to its ability to overcome the limitations of autofluorescence, scattering, and absorption inherent to shorter wavelengths. Nanoscale drug delivery platforms can strongly benefit from such imaging capabilities, facilitating noninvasive therapeutic tracking and diagnostics through the layers of biological tissue. Among nanomaterials, graphene quantum dots (GQDs) show the most potential in intrinsic NIR-II fluorescence imaging due to their photostability, biocompatibility, and low-cost/straightforward synthesis. This study for the first time evaluates all essential in vivo parameters for three most emissive GQD types including toxicity, biodistribution, and clearance. Their NIR-II fluorescence collected at 1000 nm (RGQDs, Sc-GQDs) and 1050 nm (Nd-NGQDs) noninvasively through the bodies of sedated Balb/c mice and from their organs and tissue slices helps evaluate GQD content and their organ compartmentalization. Within 21 days after injection, all GQDs show no signs of toxicity in Balb/c mice. GQDs accumulate in the liver, kidneys, spleen, lungs, heart, and bones. RGQDs mainly undergo renal clearance, while Nd-NGQDs and Sc-GQDs are excreted predominantly through the hepatobiliary and splenic systems. This study paves the way for future in vivo applications of biocompatible GQD delivery vehicles, enabling NIR-II image-guided theragnostics in multiple organs.