Combination Diagnostics In Vivo: Dual-Mode Ultrasound/NIR Fluorescence Imaging with Neodymium- and Thulium-Doped Graphene Quantum Dots
来源：ACS Publications
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.
Carbon dots and graphene quantum dots (GQDs) exhibiting NIR fluorescence already attract substantial attention in biomedical research, as they present minimal toxicity in vitro and in vivo due to their small size, water solubility, and rapid excretion. GQDs, in particular, present a versatile platform that has been successfully utilized in our work for multiple imaging, sensing, and delivery applications. They deliver several drug and gene payloads, including molecular therapeutics, plasmids, and nucleic acids, and, when functionalized with hyaluronic acid, can target cancer cells, potentially enabling small tumor detection. This application is particularly relevant for dual-mode USI/fluorescence contrast agents due to the apparent limitation of the noncontrast USI in small tumor identification. While dual-contrast capabilities are not observed with GQDs on their own, doping those with rare earth metals facilitates ultrasound signal enhancement in vascular and animal tissue phantoms. Rare earth metal dopants such as Tm and Nd also contribute to the NIR fluorescence of GQDs through transitions of trivalent ions and enable multichannel NIR imaging with 808 nm excitation In the present work, we advance the exploration of ultrasound and NIR fluorescence imaging capabilities of these materials to in vivo and ex vivo studies. In addition to providing proof of concept, this work evaluates retention/clearance times as well as the optimal times of dual-mode imaging with GQD contrast agents in different organs. The development of such dual-mode contrast agents can enhance the overall performance of disease diagnostics, eliminating the need to use complicated and, in some instances, toxic nanobubble/dye systems. Clinically, such dual-mode imaging techniques can provide a critical advantage in the detection of small cancer tumors, inflammation sites, and sentinel lymph node biopsies.