<p>Vanillin is a widely used flavoring agent in the food, pharmaceutical, and cosmetic industries; however, its excessive intake may pose potential health risks, necessitating sensitive and reliable detection methods. In this work, a novel and cost-effective electrochemical sensor was developed based on Mn_0.5Ni_0.5Co₂O₄ (MNC) spinel decorated with g-C₃N₄@CeO₂ nanoparticles (NPs). The effect of different loading ratios of g-C₃N@CeO₂ NPs on the sensor performance was systematically evaluated to identify the optimal composition. The incorporation of g-C₃N₄@CeO₂ NPs significantly enhanced the electroactive surface area, accelerated electron transfer kinetics, and improved the electrocatalytic activity toward vanillin oxidation. The synthesized nanocomposites were characterized by spectroscopic, structural, morphological, and electrochemical techniques, confirming the successful fabrication and improved electrochemical properties. Under optimized conditions, the sensor exhibited a low limit of detection (LOD) of 6 nM and a limit of quantification (LOQ) of 19 nM, along with two linear response ranges of 0.006-0.4 µM and 1-1000 µM. Additionally, a wide detection range up to 4000 µM was achieved. The sensor demonstrated excellent selectivity, reproducibility, and long-term stability. Its practical applicability was verified by the accurate determination of vanillin in real food samples, yielding satisfactory recovery and precision. These findings highlight the potential of surface-engineered spinel/NPs nanocomposites as efficient platforms for sensitive electrochemical sensing applications.</p>