Coordination-Engineered Ru-Nb2O5 Nanoreactor Integrated with Histidine-Functionalized Graphene Quantum Dot for Ultrasensitive and Selective Electrochemical Detection of Ascorbic Acid in Fresh Juices
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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-Nb 2 O 5 -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 2 to yield Ru-Nb 2 O 5 -HGQD. The resulting Ru-Nb 2 O 5 -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 Nb 2 O 5 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-Nb 2 O 5 -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.
