Engineering FeOOH/Fe₂O₃@Carbon Interfaces With Biomass‐Derived Carbon Nanodot/Iron Colloids for Efficient Redox‐Modulated Dopamine Voltammetric Detection

Abstract

The Fe2+/Fe3+ redox couple is effective for voltammetric detection of trace dopamine (DA). However, achieving adequate concentrations with high electroactive surface area (ECSA), DA affinity, and fast interfacial charge transfer is challenging. Consequently, most reported Fe‐based sensors have a high nanomolar range detection limit (LOD). Herein, we address these limitations by manipulating the phase and morphology of FeOOH/Fe2O3 heterojunctions anchored on sp2‐carbon. FeOOH/Fe2O3 is synthesized by variable temperature aging of unique Fe5H9O15/Fe2O3@sp2‐carbon colloidal nanoparticles, which form via chelation between biomass‐derived carbon nanodots (CNDs) and Fe2+ ions. At 27°C and 120°C, Fe5H9O15/Fe2O3@sp2‐carbon transforms into β‐FeOOH/Fe2O3 nanoparticles and α‐FeOOH/Fe2O3 nanosheet, respectively. The β‐FeOOH/Fe2O3 interface exhibits higher eg orbital electron occupancy than α‐FeOOH/Fe2O3, thereby facilitating oxygen adsorption and the generation of Fe2+/Fe3+ sites near the polarization potential of DA. This facilitates interfacial electron transfer between Fe3+ and DA. Moreover, its nanoparticle morphology enhances ECSA and DA adsorption compared to α‐FeOOH/Fe2O3 nanosheets. With a LOD of ~3.11 nM, β‐FeOOH/Fe2O3 surpasses the lower threshold in humans (~10 nM) and matches noble‐metal sensors. Furthermore, it exhibits selective detection of DA over 10 biochemicals in urine. Therefore, the β‐FeOOH/Fe2O3@sp2‐C platform holds promise as a low‐cost, easy‐to‐synthesize, and practical voltammetric DA monitor.