Enhanced amperometric detection of tumor biomarker vanillylmandelic acid using NiMoO₄@C₃N₅ hybrid nanostructures

Accurate and sensitive detection of tumor biomarkers is critical for early cancer diagnosis and prognosis. In this study, a NiMoO₄@C₃N₅ hybrid nanostructure-modified glassy carbon electrode was developed for the amperometric detection of vanillylmandelic acid (VMA), a key biomarker for neuroblastoma and pheochromocytoma. The NiMoO₄ nanorods were synthesized using a sonochemical method, while C₃N₅ nanosheets were prepared by thermal polymerization, and their integration into a hybrid composite was achieved through ultrasonic-assisted dispersion. The hybrid composite was prepared through ultrasonic-assisted dispersion, combining the high conductivity of NiMoO₄ with the large surface area of C₃N₅ to enhance charge transfer. The structural and morphological characteristics of the synthesized materials were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Electrochemical characterization using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) revealed the superior charge transfer properties of the NiMoO₄-C₃N₅ hybrid, attributed to the synergistic effect of the high conductivity of NiMoO₄ nanorods and the large surface area of C₃N₅ nanosheets. The sensor exhibited an excellent amperometric (i-t) response towards VMA oxidation using the electrolyte, 0.1M of PBS (pH 3.0) at an applied potential of 0.95 V, with a wide linear detection range of 0.0125 to 183.66 μM and an ultra-low limit of detection of 1.5 nM. The high sensitivity, excellent anti-interference capability, and long-term stability of the modified electrode were demonstrated through selective detection studies in the presence of common interfering biomolecules. Real sample analysis performed with spiked human urine and blood samples showed high recovery rates, confirming the sensor's applicability in clinical diagnostics. The synergistic combination of NiMoO₄ nanorods and C₃N₅ nanosheets represents a novel approach that improves sensitivity and stability compared to existing sensors, making it suitable for point-of-care tumor biomarker detection.