Abstract
Early and precise detection of the amyloid-β (Aβ) aggregates is a critical factor in understanding Alzheimer's disease (AD) pathology. Current fluorescent probes for detecting Aβ plaques suffer from poor photostability, low selectivity, and ineffective blood-brain barrier (BBB) permeability, hindering in vivo imaging efficacy. Herein, we develop the first demonstration of nitrogen-doped graphene quantum dots (N-GQDs) as multifunctional fluorescent probes enabling sensitive, selective, and real-time in vivo and ex vivo imaging of Aβ aggregates in an AD rat model that overcomes previous limitations. Unlike conventional organic dyes, our N-GQDs combine high photostability with enhanced biocompatibility (cytotoxicity <10% at 250 µg mL(-1)) and high quantum yield (57.3%). Their nanoscale size (7.4 nm) facilitates efficient BBB penetration and rapid clearance, addressing a major challenge in existing Aβ imaging agents. Nitrogen doping increases the affinity and selective binding interactions of GQDs with Aβ aggregates by introducing active sites and modifying their electronic structure. N-GQDs showed a fluorescence enhancement specifically upon binding to Aβ(25-35) aggregates, providing sensitive detection at concentrations as low as 1.6 µM. Molecular docking analysis confirmed a strong and stable interaction (-57.4 kcal mol(-1)) between N-GQDs and Aβ(25-35) aggregates, supporting the observed selectivity. Following intravenous injection of the N-GQDs, the fluorescent intensity in the brain of the AD model rats showed a ∼2-fold increase compared to that of control rats, consistent with ex vivo biodistribution studies. These findings establish N-GQDs as the first graphene-based platform for non-invasive, selective in vivo detection of Aβ plaques, offering them as a diagnostic agent for AD pathology.