Near-infrared fluorescence and contrast-enhanced ultrasound imaging with graphene quantum dots

Valimukhametova, Alina

Item

Near-infrared fluorescence and contrast-enhanced ultrasound imaging with graphene quantum dots

Valimukhametova, Alina

Date

2025-04-28

Abstract

Near-infrared (NIR) fluorescence and contrast-enhanced ultrasound imaging provide several advantages over other diagnostic imaging methods, including versatility in imaging and sensing, non-invasiveness, and, most importantly, cost-effectiveness. The combination of two biomedical imaging techniques, ultrasound and fluorescence 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 combining them in one versatile platform, in graphene quantum dots (GQDs). Here, we developed six types of highly biocompatible GQDs exhibiting spectrally-separated fluorescence in the NIR range with NIR excitation. Their optical properties in the NIR are attributed to either rare-earth metal dopants (Ho-NGQDs, Yb-NGQDs, Nd-NGQDs, Tm-NGQDs) or defect-states (NGQDs, RGQDs). Moderate up to 1.34% quantum yields of these GQDs are well-compensated by their remarkable >4 h photostability. At the biocompatible concentrations of up to 0.5–2 mg ml-1 GQDs enable in vitro imaging in the NIR spectral region. GQDs doped with rare-earth metals exhibit ultrasound enhancement in vascular phantoms and biological tissue. In vivo studies demonstrate that GQD NIR fluorescence collected at 1000 nm (RGQDs) and 1050 nm (Nd-NGQDs) non-invasively through the bodies of sedated Balb/c mice and from their excised organs can help evaluating GQD tissue content and organ compartmentalization. Within twenty-one days after injection, both GQDs show no signs of acute toxicity in Balb/C mice. They accumulate in the liver, kidneys, spleen, lungs, heart and joints. RGQDs mainly undergo renal clearance, while Nd-NGQDs excrete predominantly through the hepatobiliary and splenic systems. Injected intravenously, Nd-NGQDs exhibit ultrasound enhancement and NIR fluorescence in liver, spleen, and kidneys. The best agreement is achieved between the two imaging techniques for Tm-NGQDs in the liver at 12 h post injection and for Nd-NGQDs in the liver at 24 h, spleen at 6 and kidneys at 12 hours post injection, suggesting the optimal timeline for imaging. Intraperitoneally-injected Nd-NGQDs demonstrate a greater consistence between ultrasound enhancement and NIR fluorescence within 1 – 48-hour time points in all imaged organs. Metal-doped GQD contrast agents developed for the first time in this work therefore hold significant promise for dual-mode ultrasound/fluorescence imaging. They can offer improved diagnostics and therapeutic delivery monitoring for multiple organ targets and conditions including cancer, kidney damage, and inflammatory diseases.