Coordination-engineered Ru-NbO nanoreactor integrated with histidine-functionalized graphene quantum dot for ultrasensitive and selective electrochemical detection of ascorbic acid in fresh juices.

A coordination-driven synthetic approach is proposed to engineer Ru-NbO-HGQD nanoreactor through synergistic assembly of histidine-functionalized graphene quantum dot (HGQD). The approach involves sequential coordination of niobium oxalate and ruthenium chloride with HGQD, forming water-soluble Ru/Nb-HGQD precursor, followed by two-stage controlled thermal annealing in N to yield Ru-NbO-HGQD. The resulting Ru-NbO-HGQD offers a quasi-spherical morphology (46.5 ± 1.4 nm) featuring Ru-embedded interconnected nanochannels, abundant low-valent Nb species, and graphene-modified interfaces. This unique architecture facilitates enhanced electron/ion transport kinetics, exposes catalytically active sites, and amplifies interfacial interactions with polar electrolyte. The incorporation of NbO elevates the electrochemically active surface area by 1.55-fold, resulting in more than 2.24-fold enhancement in catalytic activity over Ru-HGQD. The ascorbic acid sensor with Ru-NbO-HGQD demonstrates a broad linear range (0-600 μM) at 0.056 V, an ultralow detection limit (1.2 × 10 M, S/N = 3), and exceptional selectivity against interferents. Long-term stability and reproducibility further validate its reliability for ascorbic acid quantification in fresh juice. This work also establishes a paradigm for designing high-performance oxide-supported metal nanomaterials in sensing, catalysis, and energy storage and conversion.