Plasmonic MoO 3-x nanosheets by anodic oxidation of molybdenum for colorimetric sensing of hydrogen peroxide

Hydrogen peroxide sensing is crucial for various medical diagnostics and industrial monitoring. On the other hand, doped metal oxides have recently emerged as cost-effective materials with localized surface plasmon resonance (LSPR) for colorimetric sensing of hydrogen peroxide. In this paper, using a simple anodic oxidation method, plasmonic MoO colloidal nanosheets with deep blue color were fabricated and examined for the colorimetric sensing of hydrogen peroxide. X-ray photoelectron spectroscopy (XPS) revealed the presence of a considerable level of oxygen vacancy in the nanosheets composition. Depending on its concentration, hydrogen peroxide weakens the LSPR and the blue color of colloids with a sigmoidal sensing behavior. The impact of anodizing potential (10, 20, and 30 V) and time on a sensing performance was investigated and a limit of detection (LOD) as low as 0.2-0.9 μM was obtained. Furthermore, it was found that the LSPR undergoes redshift and the optical bandgap increases in a sigmoidal manner with analyte concentration that was explained by the existing theory on plasmonic semiconductors. To make a colorimetric assay, we immobilized MoO nanosheets on felt fibers, which was observed by scanning electron microscope (SEM) images. The assay was examined to detect hydrogen peroxide by the naked eye in the concentration range of 800 μm to 100 mM and was analyzed using digital image analysis. Overall, our study develops a facile approach to produce MoO nanosheets to detect hydrogen peroxide at the human-positive diabetes level (2.8-5.6 mM).