Electrochemical hydrogen peroxide detection on flavin adenine dinucleotide-functionalized carbon nanotubes: Experimental and DFT insights.

Hydrogen peroxide (H2O2) is an important analyte in biological, environmental, and industrial systems, requiring sensitive and reliable detection methods. Herein, we report an electrochemical sensing platform based on Flavin Adenine Dinucleotide (FAD) adsorbed onto Multi-Walled Carbon Nanotubes (MWCNTs) and immobilized on a Glassy Carbon Electrode (GCE) for the sensitive detection of H2O2. The sensing assembly was characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry. The platform exhibited a linear response to H2O2 in the 0.200-2.000 mM range, with a sensitivity of 89.17 μA/mM, a detection limit (LOD) of 17.3 μM, and a quantitation limit (LOQ) of 57.7 μM. The sensitivity was enhanced 12.8-fold compared to a FAD-free platform, which is attributed to efficient surface-confined electron transfer, redox activity localized on the isoalloxazine ring, and structural flexibility enhancing electronic coupling, as supported by Density Functional Theory (DFT) calculations. Experimental results confirmed FAD adsorption on the sensing platform surface and revealed a catalytic EC' mechanism, where FAD acts as a redox mediator facilitating the electrochemical reduction of H2O2. This mechanistically supported sensing platform provides a robust, rapid, and highly sensitive method for H2O2 detection, with potential applications in biomedical, environmental, pharmaceutical, and food analysis.