MnO2 polymorph selection for non-enzymatic glucose detection: An integrated experimental and density functional theory investigation

Abstract Herein, different polymorphs ( α, β, γ and δ ) of MnO 2 have been synthesized and its electrochemical sensing behaviour was scrutinized with glucose as a probe molecule. Comparative morphology and structural features of all the polymorphs of MnO 2 were investigated through Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), micro-Raman and X-ray photoelectron spectroscopy (XPS). Evaluation of electrocatalytic activity towards glucose oxidation was performed by cyclic voltammetry and chronoamperometry techniques. Among all, α- MnO 2 has augmented sensitivity over the tested range (5 μM–855 μM) and the oxidation reaction is governed by a diffusion controlled process. To support our experimental findings, bonding and charge transfer mechanism of glucose molecules on different phases of MnO 2 surfaces have been analysed by employing the state of the art Density Functional Theory (DFT) simulations. Higher binding energy of the glucose molecule and the maximum charge transfer from O 2p orbital of glucose to Mn 3d orbital of α- MnO 2 justifies the higher glucose sensing activity of the alpha phase as observed in the experiment. Furthermore, a wide linear range (5 μM to 855 μM), good specificity and stability of the designed sensor widens its application in the future sensing platform.