Tailoring Surface and Electrochemical Properties: Effect of Acid, Silane, and Epoxy Functionalization on γ-MnO₂ Electrodes for <scp>l</scp>-Glutamine Detection

The functionalization of MnO2 electrodes plays a crucial role in optimizing their electrochemical performance and sensing capabilities. In this study, acidified, silanized, and epoxy-functionalized γ-MnO2 electrodes are synthesized through a controlled modification process to tailor their surface chemistry and electrochemical behavior. The structural and morphological characterizations confirm distinct surface modifications, while electrochemical studies reveal significant variations in charge transfer resistance, electroactive surface area, and electron transfer kinetics. Among the modified electrodes, silanized-MnO2 achieves the highest sensitivity (3.98 μA cm–2 nM–1), owing to its amine (−NH2) and siloxane (Si–O) functional groups enhancing charge transfer interactions. While acidified-MnO2 achieves the lowest limit of detection (LOD, 239 pM), its higher charge transfer resistance limits its sensing efficiency. Epoxy-MnO2, with its superior electroactive surface area (6.37 × 10–2 cm2), demonstrates a lower LOD (285 pM) and highest operational stability (76.8% response retention after 4 weeks), making it the most promising candidate for long-term applications. This work pioneers the first electrochemical glutamine sensor operating in the nanomolar regime, offering an innovative and scalable approach for real-time biomarker detection. Additionally, these findings suggest the critical role of surface functionalization in tuning γ-MnO2 electrodes for electrochemical applications, offering pathways for enhancing sensor performance in biomedical monitoring.