Coordination-Engineered Ru-Nb2O5 Nanoreactor Integrated with Histidine-Functionalized Graphene Quantum Dot for Ultrasensitive and Selective Electrochemical Detection of Ascorbic Acid in Fresh Juices

Abstract The practical deployment of present electrochemical sensors for ascorbic acid detection in complex biological matrices is constrained by inadequate selectivity and sensitivity. The paper proposes a coordination-driven synthetic approach to engineer Ru-Nb2O5-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 N2 to yield Ru-Nb2O5-HGQD. The resulting Ru-Nb2O5-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 Nb2O5 elevates the electrochemically active surface area by 3.75-fold, resulting in more than 7-fold enhancement in catalytic activity over Ru-HGQD. The ascorbic acid sensor with Ru-Nb2O5-HGQD demonstrates a broad linear range (0–500 µM) at 0.056 V, an ultralow detection limit (1.2×10− 8 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.