Direct Electrochemical Determination of Quercetin in Onion Samples Using Vertically Ordered Mesoporous Silica Films

ABSTRACT Quercetin (Qu), a dietary flavonoid with potent antioxidant and bioactive properties, requires accurate quantitation in food matrices to ensure health benefits and consumer safety. Conventional determination methods often suffer from high cost, complex operation, or susceptibility to electrode fouling. Herein, we report a high‐performance electrochemical sensor for Qu detection, employing nitrogen‐doped graphene quantum dots (NGQDs)‐electrochemically reduced graphene oxide (ErGO) nanocomposite integrated with vertically‐ordered mesoporous silica films (VMSF). This work distinguishes itself by uniquely combining the signal‐amplifying NGQDs‐ErGO nanocomposite with the antifouling VMSF nanochannels in a single in situ fabrication step, achieving both high sensitivity and exceptional robustness for direct detection in complex samples. The NGQDs‐graphene oxide (GO) nanocomposite was dropped onto gold electrodes (AuE), followed by in situ reduction of GO to ErGO during rapid VMSF growth via electrochemically assisted self‐assembly method. The synergistic combination of NGQDs and ErGO provides enhanced conductivity, abundant active sites, and improved analyte enrichment, while VMSF nanochannels confer strong anti‐fouling capabilities, molecular selectivity and preconcentration ability for Qu through hydrogen bonding effect. The developed VMSF/NGQDs‐ErGO/AuE sensor demonstrated excellent analytical performance, featuring a low detection limit of 61 nM, a high sensitivity of 1.37 µA/µM, and two wide linear ranges of 0.1–10 µM and 10–100 µM. It also showed outstanding reproducibility and stability for direct Qu detection in complex onion samples, with minimal interference from coexisting species. This strategy offers a versatile platform for antioxidant monitoring, quality control, and safety assurance in the food industry.