Non-enzymatic Glucose Detection Mechanism on Pt: A Surface Interrogation Scanning Electrochemical Microscopy Investigation.

Abstract

Understanding the surface-state dependence of glucose electrooxidation on platinum is essential for advancing non-enzymatic glucose sensing. Mechanistic assignment based on classical cyclic voltammetry (CV) remains ambiguous because CV convolves glucose adsorption-dehydrogenation with the simultaneous formation and removal of Pt-oxygenated species. Here, we investigate glucose electrooxidation on polycrystalline Pt in phosphate buffer solution (pH 7.3) by combining conventional voltammetry with surface interrogation scanning electrochemical microscopy (SI-SECM), which enables quantitative titration of surface-bound oxidizing equivalents. Using the [Ru-(NH₃)₆]^3+/2+ redox couple as a mediator, the Pt substrate was pre-polarized for 30 s at controlled potentials, then switched to open circuit while tip voltammetry generated Ru²⁺ to titrate oxidising species (PtOx_ads) formed on the substrate. SI-SECM reveals that titratable PtOx_ads begins to form at ∼0.61 V vs RHE and increases with the increase of the pre-polarizing potential. Results evidence how, in the 0.61-0.81 V potential range, commonly associated with incipient hydroxide/OH, these oxidizing species are not consumed by glucose. In contrast, at more anodic potentials (≥0.9 V), the PtOx_ads amount is significantly reduced in the presence of glucose, indicating direct involvement of higher-potential Pt-oxide species in glucose oxidation. These outcomes clarify the potential-dependent reactivity of Pt-oxygenated layers in neutral media and demonstrate SI-SECM as a powerful approach to decoupling and quantifying surface oxidants that cannot be resolved by CV alone.