Combination Diagnostics In Vivo: Dual-Mode Ultrasound/NIR Fluorescence Imaging with Neodymium- and Thulium-Doped Graphene Quantum Dots

The combination of two biomedical imaging techniques, fluorescence and ultrasound imaging, can uniquely offer enhanced anatomical visualization, sensitivity, and specificity necessary for improved diagnostic accuracy in detecting small tumors, tracing therapeutic delivery, and guiding biopsies. This work aims to harness the advantages of highly deterministic fluorescence imaging and deeply penetrating ultrasound diagnostics in neodymium- and thulium-doped graphene quantum dot (Nd-NGQD and Tm-NGQD) ultrasound/near-infrared (NIR) fluorescence contrast agents. These biocompatible nanostructures are tested for dual-mode fluorescence/ultrasound imaging in vivo in live sedated BALB/c mice as well as in animal organs. Injected intravenously (IV), Tm-NGQDs and Nd-NGQDs exhibit ultrasound enhancement and NIR fluorescence in the liver, spleen, and kidneys. The best agreement is achieved between the two techniques in the liver at 12 h for Tm-NGQDs and in the liver at 24 h, in the spleen at 6 h, and in the kidneys at 12 h for Nd-NGQDs, suggesting the optimal timeline for imaging. IP-injected Nd-NGQDs demonstrate a greater consistency between ultrasound enhancement and NIR fluorescence within 1-48 h time points in all imaged organs. Metal-doped GQD contrast agents developed for the first time in this work hold significant promise for dual-mode ultrasound-fluorescence imaging, paving the way for improved diagnostics and therapeutic monitoring.